Crate V5 mods... anyone?

[jim p]

On the variable voltage regulator I am posting a mark up from the schematic at the Sewatt web site. I think it can be improved by adding decoupling to the gate of the mosfet pass regulator to reduce power supply ripple 100nF will give a rejection to a 25th of the ripple on the raw supply. The circuit at Sewatt shows a zener diode that has a dual purpose first to protect the mosfet from breakdown due to gate to source voltage being exceeded. Then combined with the 10 to 15 ohm resistor can provide some current limiting. But the current limit has a wide range due to maximum to minimum zener voltage and the variation in threshold voltage from mosfet to mosfet being 2 to 4 volts. I am posting another circuit that uses a TL431 shunt regulator that will give precise current limiting independent of the mosfet used. The TL431 is 2.5 volts from anode to reference pin with 25 ohms that will give you current limit at 100mA (2.5 volts divided by 25 ohms equal to 100mA) for different current limit change the resistor value. Also can parallel this current sense resistor with a divider or pot to adjust or change the current limit. The power rating of the 25 ohm resistor needs to be ½ watt to 1 watt with the TL431 circuit. You will still need a zener diode in the circuit when using the TL431 to protect it and the mosfet that you use.
For the mosfet I would use the IRFS820 it is an electrically isolated TO 220 style package which is safer due to the raw plate supply (350 volts) on the drain of the mosfet. At Sewatt the mosfet has been attached to the amplifier chassis to use the chassis as a heat sink so the isolated package makes this eayser and safer. You will need thermal grease (pigeon crap) between the chassis and the mosfet for good thermal contact along with screwing it down well to the chassis. If you dial down the plate supply quite a bit you will probably be putting around 6 watts into the mosfet so it will need some surface area to dissipate that heat.

As far as what supply to vary I would just vary the voltage to the output tube (plate supply and screen grid) splitting off the preamp (12AX7) section this way you do not need to worry about causing grid current to flow on the control grids of the 12AX7 when you change supply voltages. If you go to Sewatt and check out the VVR schematic for the Valve Jr. you will see coupling caps added to the control grids of the 12AX7 to prevent grid current flow with supply voltage adjustment (going from low plate voltage to high plate voltage)

At Sewatt in the FAQ and schematic section for the valve Jr. they have an illustration of using a terminal strip to wire this regulator circuit up that you may find useful. On the parts front Mouser electronics carries the LT431 (LM431) and IRFS820 I think they are 37 cents and 95 cents each.

PS: Was just looking and found that the IRFS820 is going obsolete so insted you can use the FDPF5N50 mosfet

Have fun and be safe

[timothymegg]

Hey guys!
I would like to add a cooling fan - the computer variety - to the amp chassis to help keep the tubes cool. Does anyone have any suggestions on how I can power a 12v DC fan that draws about 1.5 to 3 watts? It would be nice to have a switch and/or be able to have the fan on even when the power to the amp is off to continue cooling the tubes after power down?

Again, thanks to Jim P and Deafelectromark for their great help in modding the amp I have already modded.
Peace,
Timothy

[timothymegg]

I modded my amp as I have stated in post 240.
I left D9 and D10 in where deafelectromark took them out.
What happens to the signal when I take them out?
I am experiencing that the amp seems to break up rather quickly with humbuckers. If I remove D9 and D10 will that reduce the signal and give me a later breakup?

Thanks again Jim P - here's another one for ya ;)
Timothy

[tunghaichuan]

Timoth,

You might try running a 240v AC fan on the 120v AC from the IEC connector. The fan will run slower than if powered by 240v, but all you want is some air flow across the tubes. The fan is supposed to be quieter as well. There may be some AC hum if you don't run the wires in the chassis just right.

tung



Hey guys!
I would like to add a cooling fan - the computer variety - to the amp chassis to help keep the tubes cool. Does anyone have any suggestions on how I can power a 12v DC fan that draws about 1.5 to 3 watts? It would be nice to have a switch and/or be able to have the fan on even when the power to the amp is off to continue cooling the tubes after power down?

Again, thanks to Jim P and Deafelectromark for their great help in modding the amp I have already modded.
Peace,
Timothy

[jim p]

Having D9 and D10 in or out should make no real difference. At the most they may look like a few picofards at the input vs. all the capacitance of your guitar cable it is nothing. There purpose was to protect the input to the op amp that used to be in the amplifier. You would have to have a 10 volt rms signal from the guitar to even turn the diodes on the best you could do with hot pickups and strummed chord is probably 2 volts rms as a guess. With that 2 volt signal the input triode would be clipping also.

On the fan I not sure you really need one if you are worried about the life of the tube probably make the most amount of sense to make sure the heater voltages are there typical or minimum. But if it is 12 volts you could pick the right value series dropping resistor and run it off the -12 volt supply I suppose. Also if you make the resistor high in value you can slow the fan down.

[vinyl_key]

Registered for this site after finding this thread from a Google search on the v5; excellent resource.

I ripped open my v5 a few days ago, and pulled the op amp and various resistors and caps and put in the three jumpers as instructed on post #168. The resulting sound is fantastic, a huge improvement over stock.

How much heat should be coming out of these amps? Now, I'm not sure if I just didn't notice it before, or if modding it actually made it run a bit hotter, but the top of my amp gets quite warm after playing for a bit. I usually have the gain set somewhere between 5 and 7.

Now all that's left is to replace the 12ax7 with a 12a( t or u )7 and to toss the stock speaker.
As for speaker choices, I've narrowed it down to three (all ceramic Webers):
Sig10, Sig10s, and Chicago Vintage 10 (CVC10)
Anyone have any insight on how these three speakers will sound differently, especially in the context of this amp?

Thanks :beer:

[jim p]

The mod you did should have no effect on overall temperature of the amplifier. On the speaker front I have no opinion but you may want to consider trying a 16 ohm speaker if you want the maximum volume. That is because the stock output transformer is 20:1 which is more in line with a 16 ohm load then an 8 ohm load. The Jensen Mod speakers are popular if you go with higher wattage versions the voice coil is bigger and distortion is less. There is another thread here on speakers for the Crate V5 look for that.

Glad you had no problems making the modification I tried to make as clear and simple as I could.

[deafelectromark]

Good to see that some of you still play your guitar. A great little way to get fan cooling is to get a 12 volt fan at Radio Shack and use a wall wart about 6-7 volts to make it run slower and inaudibly. I had a Peavey Classic 30 that was heating my lunch while I played and so I put a metal, outdoor electrical box in the amp with standard duplex AC outlet for the fan's plug pack and an extra outlet for effects. I put a nice long cord on it too, so I didn't need anything to power up in most venues. Whisper quiet and very cool. I just tried different warts until I got the speed of airflow and quiet that I needed- easy with a Variac, or those voltage selectable warts like at Radio Shack or other places. My amp still sings the blues and she is having a great time (I got 2 for stereo).
Mark
ROCK ON!

[stoneattic]

I ended up ordering the VVR from Hall and received it the other day. I marked up the schematic with what I believe would be correct to vary only the power stage voltages. On the attached schematic the blue line is to be cut and the mark ups in red would be the new connections/components.

Could someone who knows more than me, which isn't too hard :D , take a look and see if it makes sense?

Also, if i want to add a master volume would I just install a pot (1meg?) between C3 and pin 2 on the EL84?

Thanks!

[jim p]

I will mark up a schematic and post it but the way you have it configured there is no filter capacitor after the VVR. I think without adding another filter cap the quick and dirty way to solve that will be to replace R25 with a short. Then break the circuit where R26 hooks to C16 you should replace R26 with a 15 to 25 k (it may be best to use 25k) resistor to reduce the plate voltage on the 12AX7. Then R26 will hook to C15 + on one side and C17+ on the other side so it bypasses the VVR.
Another change I would make is to increase the grid stopper resistor value R18 a quick thing to do is to use the 4.7k that use to be R25 there.
As far as the diodes you show not sure you need them and some filter caps will have no bleeder resistor across them so they may stay charged for a while with the amp turned off.

On the master volume if you remove R31 and R16 you can hook a 500k (or 1 Meg) pot to where R31 connected to C7 then the wiper to where R31 hooked to C3 and pin 2 of EL84 and the other terminal of the pot to ground side of R16. May want to change C3 to 100pF or remove it (high frequency roll off). I would just use twisted individual wires to connect to the PCB and pot.

On the master volume and feedback you could have both but you cannot use them both at the same time. When you use master volume the gain between the 12AX7 and output tube is changing with you adjusting volume so no way to know what feedback ratio to use. So you would have to max out the master volume then use feedback so the gain control will be your volume control as if you had no master volume. Also with the Variable voltage regulator the feedback would not work due to gain of output tube changing with changing plate voltage. Plus feedback makes going into distortion abrupt so it would not work well with using variable voltage on the plate supply.

[SciHi]

Also, if i want to add a master volume would I just install a pot (1meg?) between C3 and pin 2 on the EL84?

I did my master volume a little different with a 250K pot but really like the results. I tried Jim's NFB with the pot, and conventional NFB, but prefer the control and tone with the master volume. My v5 combo now sounds better than my valve jr combo, I am going to have to mod it more now...

http://i615.photobucket.com/albums/tt237/scihibmxer/v5el84modsmv.jpg

http://i615.photobucket.com/albums/tt237/scihibmxer/mastervolumeconnections.jpg

[SynySter_SlaSh]

Hi ive been reading through for ages, and it seems that all the modified schematics are being critisized for being wrong.

I would like to do the bypass op-amp mod

can someone link me the correct schematic and/or circuit pictures

if you realy wanna, you can do a step by step for a non electronics savy person

thanks

[jim p]

Hi ive been reading through for ages, and it seems that all the modified schematics are being critisized for being wrong.

I would like to do the bypass op-amp mod

can someone link me the correct schematic and/or circuit pictures

if you realy wanna, you can do a step by step for a non electronics savy person

thanks
It is not all the schematics that have been noted as being wrong and if you do a modification based on a schematic that is in error things won't work. So if no one points out a mistake it can cause someone a lot of grief. Not trying to be critical just trying to prevent people from having problems by going down the wrong path.

With that aside post #168 is an easy way to get rid of the op amp and move the volume control to where it belongs. I think it is well documented in pictures and schematic to make it easy to follow. It worked ok as far as the post #246 but he is adding a variable voltage regulator now so his skill level is reasonably high.
Any of this is all up to your knowledge of electronics and skill level in making modifications. Best thing is to look closely at what is being described and if it makes sense and you are comfortable with it go for it.
If you go to the sewatt web site in the questions and FAQ section for the Valve Jr they may have some write ups on making modifications that will give you a better feel for the task.

Over all this is like any other DIY project such as a brake job on your car or fixing a facet it is relative to how much you know about how the system works. On the down side you can't ask the guy at the parts counter about it.

[SciHi]

I would like to do the bypass op-amp mod

can someone link me the correct schematic and/or circuit pictures

I think it is more of personal preferrence. There are probably a hundred ways to jumper the opamp, Jim's is likely one of the simplest. I started doing just the opamp mods Jim mentioned, and added the volume pot in the "on indicator light" location. This worked quite well, but I was not totally satisfied and wanted to compare it to the opamp jumper mod. So all I needed to do was pull a couple of resistors and cap to do the jumper. I had already put the 1M resistor across the input jack, and then just changed R1 to 10K (these are valve junior mods). SEWATT, the valve junior section, is a really good place to read up on the many potential ways to mod single ended amps.

I like my v5 better without the opamp. There are also many options for the tone control, I tried the Marshall 18 watt lite and like the results. But these mods are all based on personal preference, the tone I like. But many of us are just hackers with a soldering iron, Jim has the technical background in electronics. What is right to me, is what sounds best with my HB guitars. If you play single coils, you would need to modify some of the values I used.

http://i615.photobucket.com/albums/tt237/scihibmxer/v5inputmod.jpg

http://i615.photobucket.com/albums/tt237/scihibmxer/v5marshalltonemod.jpg

[SynySter_SlaSh]

Which wire should i be using to mod this ? (jumper wire etc)

is this suitable...

http://cgi.ebay.co.uk/Shielded-1-conductor-Guitar-Circuit-Wire-foot_W0QQitemZ120439332509QQcmdZViewItemQQptZUK_Gu itar_Accessories?hash=item1c0abe5e9d&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A1683|240%3A13 18|301%3A1|293%3A1|294%3A50

EDIT** or should it be non shielded.....

http://cgi.ebay.co.uk/Guitar-non-shielded-circuit-wire-White-Buy-per-foot_W0QQitemZ250451544291QQcmdZViewItemQQptZUK_Gu itar_Accessories?hash=item3a501348e3&_trksid=p4634.c0.m14.l1262&_trkparms=|301%3A1|293%3A1|294%3A30

[ibanezjunkie]

im not a modding expert, Synyster Slash, but im pretty sure its a good idea to use shielded wire.

[SciHi]

Which wire should i be using to mod this ? (jumper wire etc)

Jumpers on the pcb, I just use small wire, 22-24 gauge is fine. If it is a single component or very close, I just use the cut off wire leg of a resistor or capacitor. Sometimes I will put the jumper on the bottom if things are packed real tight on top. If I am running to a pot or switch mounted to the chasis and it is a low voltage signal, then I will usually use shielded audio cable, like this, http://www.alliedelec.com/Images/Products/Datasheets/BM/BELDEN_WIRE_AND_CABLE/214-1557.PDF mostly because I have access to it. This seems like a better source for amp parts/wire: http://cgi.ebay.co.uk/CABLE-WIRE-600V-ORANGE-22awg-11Amp-3-METRES_W0QQitemZ370203385379QQcmdZViewItemQQptZUK_ Consumer_VintageAudio_RL?hash=item5631d75e23&_trksid=p4634.c0.m14.l1262&_trkparms=%7C301%3A0%7C293%3A1%7C294%3A30

Old computers are a good source for small shielded wire, usually from the cd drives, this is very similar to what the valve junior uses. Higher voltage, or strong signal can usually be done with twisted pairs. Thanks Dr. Mumbles for adding the specifics...

http://i615.photobucket.com/albums/tt237/scihibmxer/jumperwire.jpg

[rock_mumbles]

Which wire should i be using to mod this ? (jumper wire etc)...

I use wire from a burned out computer power supply to connect volume or tone pots and for runs of a few inches on a circuit board. A friend bought a professionally modded amplifier and all of the jumpering was done with single conductor stranded wire.

In my V5 I jumped around the OP-amp with a new 68K grid resistor, but I reworked the amp circuit quite a bit.

I use (old) computer sound card cables (CD to sound card) when I want to use small shielded cable, but again only for carrying the signal NOT for supplying voltage to the tubes, etc.

One of the main things about the wire you use is the insulator on the wire, some wire is really hard to solder because the insulation melts so easy.

[stoneattic]

I will mark up a schematic and post it but the way you have it configured there is no filter capacitor after the VVR. I think without adding another filter cap the quick and dirty way to solve that will be to replace R25 with a short. Then break the circuit where R26 hooks to C16 you should replace R26 with a 15 to 25 k (it may be best to use 25k) resistor to reduce the plate voltage on the 12AX7. Then R26 will hook to C15 + on one side and C17+ on the other side so it bypasses the VVR.
Another change I would make is to increase the grid stopper resistor value R18 a quick thing to do is to use the 4.7k that use to be R25 there.
As far as the diodes you show not sure you need them and some filter caps will have no bleeder resistor across them so they may stay charged for a while with the amp turned off.

On the master volume if you remove R31 and R16 you can hook a 500k (or 1 Meg) pot to where R31 connected to C7 then the wiper to where R31 hooked to C3 and pin 2 of EL84 and the other terminal of the pot to ground side of R16. May want to change C3 to 100pF or remove it (high frequency roll off). I would just use twisted individual wires to connect to the PCB and pot.

On the master volume and feedback you could have both but you cannot use them both at the same time. When you use master volume the gain between the 12AX7 and output tube is changing with you adjusting volume so no way to know what feedback ratio to use. So you would have to max out the master volume then use feedback so the gain control will be your volume control as if you had no master volume. Also with the Variable voltage regulator the feedback would not work due to gain of output tube changing with changing plate voltage. Plus feedback makes going into distortion abrupt so it would not work well with using variable voltage on the plate supply.


jim_p, thanks for the schematics, etc.

I believe there is a mistake in the schematic for the VVR though. Your text says to replace R26 with a 25K, but the schematic say R28.

I was showing diodes because the instructions with the VVR said they sould be used when using the VVR to control the power tubes only to prevent the two B+ circiut (VVRed and non-VVRed) from interacting.

I'm not following your last paragraph regarding feedback. Are you saying that the master volume and VVR will conflict? Excuse my ignorance please. I'm still learning my way around tube amps. I have a basic understanding of how tubes work and have been doing a lot of reading, but some of the intricacies still elude me.

[jim p]

I'm not following your last paragraph regarding feedback. Are you saying that the master volume and VVR will conflict? Excuse my ignorance please. I'm still learning my way around tube amps. I have a basic understanding of how tubes work and have been doing a lot of reading, but some of the intricacies still elude me.
Thanks for pointing out my error on the schematic; I’ll have to fix that. Still confused on the need for the diodes but they can’t hurt except on the no bleeder resistor aspect.
The last part of the post was just commenting because of another post in regard to feedback and master volume together being a problem. From what I gather you are just adding master volume and variable voltage regulator those two together should be no problem. Hope you are having no problems making the modifications. Probably would be good to post pictures of the mod and details for anyone else considering installing the VVR themselves.

I didn’t go in to detail on changing R25 to a short it will give you a filter cap after the VVR. If you look through previous posts you will find that C16 should have been a filter cap for the screen grid voltage so one side of R18 should have been hooked to it. Figure that the EL84 is ok without the lower screen grid voltage and C16 is really serving no purpose so may as well take advantage of it for this mod.

By changing R18 to 4.7k that will lower the screen grid voltage relative to the screen grid current through it. Also the higher value will be safer for the tube if the plate voltage goes lower than the screen grid voltage and the screen grid current rises. The higher value resistor should provide greater negative feedback and limit the maximum current that might pass through the screen grid.

Hope your mod is going well let us know how it works out.

[stoneattic]

Thanks for pointing out my error on the schematic; I’ll have to fix that. Still confused on the need for the diodes but they can’t hurt except on the no bleeder resistor aspect.
The last part of the post was just commenting because of another post in regard to feedback and master volume together being a problem. From what I gather you are just adding master volume and variable voltage regulator those two together should be no problem. Hope you are having no problems making the modifications. Probably would be good to post pictures of the mod and details for anyone else considering installing the VVR themselves.

I didn’t go in to detail on changing R25 to a short it will give you a filter cap after the VVR. If you look through previous posts you will find that C16 should have been a filter cap for the screen grid voltage so one side of R18 should have been hooked to it. Figure that the EL84 is ok without the lower screen grid voltage and C16 is really serving no purpose so may as well take advantage of it for this mod.

By changing R18 to 4.7k that will lower the screen grid voltage relative to the screen grid current through it. Also the higher value will be safer for the tube if the plate voltage goes lower than the screen grid voltage and the screen grid current rises. The higher value resistor should provide greater negative feedback and limit the maximum current that might pass through the screen grid.

Hope your mod is going well let us know how it works out.

Now I don't feel too bad about not following how the feedback related to what I was doing. :)

I'm just adding the MV and VVR to your IC removal mod from post 168. The 168 mod and a different speaker REALLY improved this amp. It's actually enjoyable to play now.

I was just digging though my various caps, pots and resistors and of course I don't have what I need so I'm gathering parts right now. I believe 1/2w on the resistors is all I need. On cap C1 there is an electrolytic there now, I really don't know when you use the various caps (elec, ceramic, poly, etc) over another in different applications. I assume I would use an electrolytic since that's what's there already, correct?

I'll post some pics when I finish, although I'm sure they will be embarrassing. I plan on putting the MV where the light is now and either drill a new hole for the VVR, or (I'm leaning toward) moving the switch and use that hole for the VVR.

Thanks for all your help.

[jim p]

I was just digging though my various caps, pots and resistors and of course I don't have what I need so I'm gathering parts right now. I believe 1/2w on the resistors is all I need. On cap C1 there is an electrolytic there now, I really don't know when you use the various caps (elec, ceramic, poly, etc) over another in different applications. I assume I would use an electrolytic since that's what's there already, correct?


On the wattage rating of the resistors the only one I know off hand that you need is R26 to a 25k you can just get by with a ½ watt there but a 1 watt would be better.

On the construction or type of capacitor film caps are your best then they vary by what they are made of Mylar, polyester, ect. problem being size and cost. You want your better capacitors in the signal path, the coupling capacitors such as C2 and C7. At the lower capacitance values mica caps are good ceramic capacitors capacitance value may change greatly with temperature and they can be microphonic. Electrolytic capacitors are usually just used for power supply filtering and at times if a large value is needed in a signal path such as the nopolar electrolytic capacitors used in crossover networks in speakers.

So if the capacitance value required is less than 1uF and the voltage rating is not too high you could probably find a film capacitor for that location.

Another thing about electrolytic capacitors is they can dry out so you should keep them away from the hotter components in the amplifier. I fixed a JVC TV and the basic cause of the failure was an electrolytic capacitor mounted inside of the u-shaped heat sink for the vertical deflection amplifier. Also good to keep high wattage resistors raised above the PCB for air flow.

[stoneattic]

On the wattage rating of the resistors the only one I know off hand that you need is R26 to a 25k you can just get by with a ½ watt there but a 1 watt would be better.

I also need a 1Meg resistor for the master volume, originally a 1/2 watt.


On the construction or type of capacitor film caps are your best then they vary by what they are made of Mylar, polyester, ect. problem being size and cost. You want your better capacitors in the signal path, the coupling capacitors such as C2 and C7. At the lower capacitance values mica caps are good ceramic capacitors capacitance value may change greatly with temperature and they can be microphonic. Electrolytic capacitors are usually just used for power supply filtering and at times if a large value is needed in a signal path such as the nopolar electrolytic capacitors used in crossover networks in speakers.

So if the capacitance value required is less than 1uF and the voltage rating is not too high you could probably find a film capacitor for that location.


I failed to mention that when I did your post 168 omp amp removal I didn't mod the tone control that you mentioned. I wanted to hear what just the omp amp removal sounded like. But now the tone control doesn't do much so I was going to replace C1 with a 200nf as you recommended. C1 is currently a 2.2uf (50v) electrolytic and after a quick check on mouser.com it looks like I might be limited to eletrolytics if I need the 50V.

So if cost it no object which order of film caps would you recommend?

Thanks again!

[jim p]

C1 has no more than two to three volts across it so you do not need a 50 volt capacitor there. A 6 volt or greater voltage rating will be fine. If you need the 1 Meg for R16 ½ or ¼ watt will be fine.

[SynySter_SlaSh]

This is the no op amp modification with the op amp removed a continuation of post #160. How you get the op amp out of the board is up to you, basic way is to cut off all pins and remove them one at a time. Also can desolder all the pins and remove op amp in one piece.
Steps involved in modification after removing PCB from chassis

1) Remove op amp IC1, C25, R28, R14, C5, C4, R27, R15 and R2
2) Replace R15 with a jumper
3) Jumper from op amp pin 3 to junction of C25 R2 and R1 (amplifier input jumper)
4) Jumper from pin 7 of op amp to ground via of R27 (black wire in picture)
5) Jumper from op amp pin 6 to junction of R27, R15, R7 and pin2 (grid) of 12AX7 (orange wire in photo near volume pot)

Options:
Remove R7 for higher maximum signal on grid of second triode.
Short R30 or R29 and remove C28 for more maximum signal at grid of second triode.
Remove C27 and use the vias (plated holes) in the PCB to connect rheostat (pot) to location of R27. Makes for shorter jumper runs on PCB.
Replace loss of pre emphasis for tone stack by replacing C1 with a 200nf cap so tone control will be treble boost, flat and treble cut. Or instead change R9 to approx 220k and add a Resistor and capacitor in parallel with it for treble boost.

See attached pictures.
Picture of tools used to remove op amp, resistors and capacitors. Also to remove solder from PCB vias.
If you get a vacuum desoldetring tool best to use fresh solder to make better thermal contact with solder joint to be desoldered. Also allow enough time to heat joint before pulling the trigger on the desoldering tool count in your head 1001, 1002… for 10 to 20 sec. Remember ground plane connections and large component leads will require more time for good results. Keep in mind too much time will lift the copper trace from the PCB making for a rework job.
If you see any errors please let me know, thanks.

isnt the orange wire on r14 ?
I cant see anything on pin 6 of the op amp ???

Im confused, are there jumpers on the other side of the board ?

Do you have a picture please.

EDIT!!!

I have done the mod as to how i can see it on the photo, I put it back together just enough to test it but have a couple of concerns

1. with the plastic knobs off and a lead plugged in i was holding the guitar side of the lead with one hand and turning the vol pot with the other to test the signal, it seemed a bit noisy and as i turned it up i got a bit of a shock, i cant remember in which hand tho. i put it pack together and played through it a bit with a guitar. tone is definately improved and i am yet to change the bias resister to 180 ohms. although when i touch any metal part of the guitar there is a slight pop noise ??? sort of what you get on cheaper strats where the hum goes away from touching it, it wasnt there before the mod.

any idea what ive done wrong ? (shock, pop noise)

2. it appears that the tone knob goes from 0 - 5 (like a guitar tone control) and then doesnt realy do anything from 5 - 10

sugest me some easy improvements forthis please :)

thanks

[jim p]

isnt the orange wire on r14 ?
I cant see anything on pin 6 of the op amp ???

Im confused, are there jumpers on the other side of the board ?

Do you have a picture please.

EDIT!!!

I have done the mod as to how i can see it on the photo, I put it back together just enough to test it but have a couple of concerns

1. with the plastic knobs off and a lead plugged in i was holding the guitar side of the lead with one hand and turning the vol pot with the other to test the signal, it seemed a bit noisy and as i turned it up i got a bit of a shock, i cant remember in which hand tho. i put it pack together and played through it a bit with a guitar. tone is definately improved and i am yet to change the bias resister to 180 ohms. although when i touch any metal part of the guitar there is a slight pop noise ??? sort of what you get on cheaper strats where the hum goes away from touching it, it wasnt there before the mod.

any idea what ive done wrong ? (shock, pop noise)

2. it appears that the tone knob goes from 0 - 5 (like a guitar tone control) and then doesnt realy do anything from 5 - 10

sugest me some easy improvements forthis please :)

thanks
The orange jumper (pot to grid and input signal) in the picture is in the via (PCB hole) for R14 but if you look there is a PCB trace that ties that to the pin6 via of the op amp so it is the same as pin 6. So all the jumpers required for the modification are in the picture of post #168.

You can have more hum from line pickup (60Hz) because the bass response of the amplifier was rolled off at 250Hz by the values of C24 and R14 that were used by the op amp. If you touch the strings of the guitar and the hum stops that is a ground problem somewhere (usually the guitar).

Nothing in the modification changed the grounding of the amplifier and from the noise, pop and shock you are asking about a bad ground would be the likely cause. Have you reinstalled and tightened all the screws that hold the PC board into the chassis? Are you plugged into a three prong wall outlet that has a known good ground prong? Do you have florescent lights near by if so turn them off and see if noise stops?

As far as the tone control to get treble boost you will need to change C1 to a 200nF 6 volt or greater capacitor instead of the stock 2.2uF. The op amp provided treble boost before the tube stages without it you have no boost so tone control will only cut the treble.

Before you change R17 to 180 ohms you should read up on how to measure the power dissipation of a power tube in a single ended amplifier, it is probably in these posts and out on the web (how to bias a Valve Jr) for the Valve Jr (also a SE amplifier). You will need a voltmeter and have to make voltage measurements in the amplifier with it running. You have to be careful because you will measure the plate voltage which is approx 330 volts.

Hope this helps you figure things out.

[SynySter_SlaSh]

Thanks for all your answers guys.

Now juat wondering about this:

"Options:
Remove R7 for higher maximum signal on grid of second triode."

I what way will this effect the tone of the amp ?

thanks

EDIT

Im in the uk and cant seem to find a 6v 200nf cap, only the 50v big ones. suggest me somewhere online please ?

[jim p]

You can use a capacitor (or condenser) with a higher voltage rating it would be best to use a film cap and they usually are found in the lower voltage rating. As far as removing R7 it will only have an effect at a high volume setting and it is a little safer for the control grid of the triode to have it installed. Shorting R30 and R29 would be the better choice to increase the maximum signal into the second triode (but it will reduce the gain of the first triode). If you have plenty of range on the volume control as it is now I would just leave the volume control alone. Also I have noticed that some pots are touchy at the low setting and having R7 as a 220k should help. The way the volume pot is setup with the mod of post #168 is not the best way to go just easiest way to move the volume control to between the triodes. The volume control would be better to be a potentiometer and not a rheostat as it is in this mod. A rheostat is a variable resistor so the resistance the first triode is driving changes with the volume setting. If the volume control was set up as a potentiometer the second triode would be connected to the wiper so it is connected to a variable voltage divider. Then the first triode would see a close to constant load independent of the volume setting.
As a quick temporary capacitor change if you removed C25 in one piece it is a 100nF cap so you could replace C1 with that to get some treble boost starting at 1kHz instead of 500 Hz.
Also you could change R3 to two 750 ohm resistors in series then put 2.2 uf across one of the resistors and 100nF across the other for just +3db treble boost instead of +6db as you have with 200nf across the 1.5k stock R3. (see schematic) With the split resistor there is more low frequency gain.

[stoneattic]

jim_p,

Maybe I'm over thinking this, but I'm trying to decide on what capacitor to order to replace C1 and there a quite a few different types of film capacitors (polyester, polypropylene, metalized, etc). On top of that there seems to be few choices that have 200nf. I see plenty of 220nf, is that close enough?

Also, you suggested either 500K or 1M for the MV pot. What are the advantages/disadvantages between the two? Audio taper I assume?

Any specific type of resistor (metal, carbon, etc) for the 1 watt to replace R26?

Sorry for all the questions. I can handle the mechanical end of things (mounting, soldering, etc) but I'm just starting to learn the electronics end.

thanks

[jim p]

On the capacitor metalized polyester should be fine and 220nf is an OK value. Regarding R26 the composition is not that important it is just a series dropping resistor in the power supply circuit. On the tone front legend is that you would want carbon composition in the signal path.
The master volume pot needs to be an audio (log taper) pot with 1 Meg you will get a little more gain from the triode that is the input to the output pentode say by calculation 59 with 1 Meg and 57 with 500k ohms.

[SynySter_SlaSh]

hello again. which of these is most suitable for replacing c1

http://cgi.ebay.co.uk/4-X-MALLORY-0-2uF-600VDC-POLYESTER-FILM-CAPACITOR_W0QQitemZ350114259294QQcmdZViewItemQQptZ LH_DefaultDomain_0?hash=item51846fa15e&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A2136|293%3A1| 294%3A50

http://cgi.ebay.co.uk/5-pcs-MP-Axial-Capacitor-0-2uF-600V-10_W0QQitemZ140301844908QQcmdZViewItemQQptZLH_Defa ultDomain_0?hash=item20aaa441ac&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A2136|293%3A1| 294%3A50

http://cgi.ebay.co.uk/10-condos-polyester-mylar-0-2uF-200nF-200V-10_W0QQitemZ280348133654QQcmdZViewItemQQptZFR_YO_M aisonJardin_Bricolage_ElectroniqueComposants?hash= item41460d0916&_trksid=p3286.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A2136|293%3A1| 294%3A50

thanks

[rock_mumbles]

You could make any of them work...

(my opinion)

The third one would probably be the easiest to fit into the PCB I would expect it to be the smallest of the three caps and it has radial leads.

The second and third are probably both higher quality caps than the third one but installing them may be more difficult.

The second one with axial leads (leads come out of each end) has to be mounted vertically (staked) I used a Mallory 150 series cap for C1 in my V5.

The first cap "an Orange Drop" style had radial leads but is probably a much larger cap, the large Orange drops I've used have large diameter leads which can be difficult to install into the pcb

Here's a picture of my C1 "staked" cap



http://i489.photobucket.com/albums/rr258/rock_mumbles/V5_staked_cap-480x360.jpg

[jim p]

As stated in the previous post you can use any of the three, the first ones are large and usually used for coupling caps between tube stages. Also I surfed on electronic components at yahoo.uk where I go to see the latest on F1, The tour of France what Lady Ga Ga is up to, if Amy Winehouse has fallen into a pool in a drunken fit and also the swine flu status. Found there some distributors you can buy from RSH Electronics, Rapid Electronics and ESR Electronics are a few. Found a Web site for hobbyists Called The Electronics club they have a links page with distributors on it http://www.kpsec.freeuk.com/links.htm This one http://www.bowood-electronics.co.uk/ charges 1 Pound 65p for shipping with a minimum order of 5 Pounds. So instead of just caps for your shipping you could get some other parts you may need.

[rock_mumbles]

...
As a quick temporary capacitor change if you removed C25 in one piece it is a 100nF cap so you could replace C1 with that to get some treble boost starting at 1kHz instead of 500 Hz.
Also you could change R3 to two 750 ohm resistors in series then put 2.2 uf across one of the resistors and 100nF across the other for just +3db treble boost instead of +6db as you have with 200nf across the 1.5k stock R3. (see schematic) With the split resistor there is more low frequency gain.

Hi Jim, I just did this on my "Home Bake" (5F1 ???) scratch built amp and I really like it. I previously had a 1.5K cathode resistor bypassed with a 2uf film capacitor. With the split resistor treble boost the tone was evened out, it helped to tamed the (ugly) mid-range.

Thanks, for the great tip!!!!

[timothymegg]

On to getting more treble by changing C1 do you have two 100 nf (0.1 uf) caps if so two in parallel is equal to 200nf so you could use that at C1 for a treble boost. Using 200 nf (0.2 uf) the boost will start at 550 Hz. In the case of voltage rating 50 volts is plenty you could get away with 12 volt rating easy.



I'm so happy !! I finally got around to getting a couple 100nf caps which I wired in parallel like you said replacing C1. The difference is night and day. Before the amp sounded too bassy and muffled without an eq in front of it. Now it sounds like a guitar amp again!

On another note: I re installed the R7 resistor to allow a little more headroom because the amp was breaking up too early. Now it starts to get a little crunch with hummbuckers around 4 and gets more driven from 6.5 on. Before it was breaking up as low as 2.5. So, I don't recommend taking out R7 in the mod I did in post # 240.

Thanks again to all the geeks and guitar amp freaks that put their knowledge out for adventurous guys like myself. Especially thanks to jim p and deafelectromark (manoteal) !!

Peace out!

[jim p]

The attached schematic is to make the first stage of the amplifier a JFET gain stage for overdrive. It has a minimum gain of two and a maximum gain of 10 to 20 depending on the gain of the FET installed. So if you have or are modifying the amplifier for preamp overdrive by using a master volume pot between the second triode and the output tube this will give you more gain to maybe get closer to the sound you want. I would also add a high level of brightness to the amplifier to go with this. Let me know if you need ideas on how to do that and I will post them. Also if more gain is needed the positive supply for this circuit could be increased by using a zener diode and series dropping resistor allowing for maximum gains of 30 to 60 and giving more head room for the JFET.

These changes are for an amplifier that has had the op amp removed from the amplifier.

[timothymegg]

Hey all you guys who know stuff about these things that I don't!

What tubes have you guys tried with good results for replacements to get a better sound? :confused:

I'm looking at Ruby Select tubes and JJ tubes right now so, if anyone has a recommendation with their experience on what they have done to change the sound then I am all ears.

I have already modded the amp and, the last stage seems to upgrade the tubes. First step was changing the speaker. Second, I bypassed the op amp. Third, I increased treble response in the tone circuit. Now the final step of getting some quality tubes in there.

Peace

[Rampant]

Hey all you guys who know stuff about these things that I don't!

What tubes have you guys tried with good results for replacements to get a better sound? :confused:

I'm looking at Ruby Select tubes and JJ tubes right now so, if anyone has a recommendation with their experience on what they have done to change the sound then I am all ears.

I have already modded the amp and, the last stage seems to upgrade the tubes. First step was changing the speaker. Second, I bypassed the op amp. Third, I increased treble response in the tone circuit. Now the final step of getting some quality tubes in there.

Peace

Hi matey

The valves were the first things I changed when I got mine!

I'm running a Mesa Boogie EL84 tube and a Mesa Boogie 12AT7 at the moment. I noticed an immediate improvement in tonal quality when I changed the EL84... not the night and day difference that changing the speaker makes, but a definite improvement nonetheless. Note that I'm using an alternative 12AT7 and not the standard 12AX7 - which gives a slightly lower output, but my practice room is a small box-room and has a massive mirrored wardrobe on 1 side - so I don't need the oomph. Even then I only normally play on volume 1 to 2. That's un-modified, of course, apart from the Jensen speaker...

HTH :)

Cheerz

Rampant

[jim p]

I don’t have an opinion on which is the best tube or tonal qualities of one vs. another. But one thing to look for is it really a different tube. In a lot of cases such as Grove tube or Mesa the tube is a Sovetek it may have been tested to meet there standards but the construction is the same. Electro-Harmonics and JJ tubes are at least a different construction then a tested and relabeled Sovetek so that is something to look for. If you search on this site on the subject of tubes you will find a survey on favorites.

[tunghaichuan]

I don’t have an opinion on which is the best tube or tonal qualities of one vs. another. But one thing to look for is it really a different tube. In a lot of cases such as Grove tube or Mesa the tube is a Sovetek it may have been tested to meet there standards but the construction is the same. Electro-Harmonics and JJ tubes are at least a different construction then a tested and relabeled Sovetek so that is something to look for. If you search on this site on the subject of tubes you will find a survey on favorites.

Have to agree with Jim here. Tubes are only made in a few places these days. There are two versions of the Sovtek EL84, a Slovak version made by JJ, a Chinese version and maybe another made by EH, although it could be a tested/rebranded Sovtek. EL84s are cheap enough to buy one of each and let your own ears be your guide.

tung

[stoneattic]

jim_p,

I finally got around to starting the tone, master volume and VVR mods this evening. I started by swapping C1 with a 220nf cap and then did the master volume. At that point I put it back together to test it. The tone mod really helped and made the tone pot much more useful.

The result of the master volume is kind of strange. 0 to about 4 acts as expected, but from 4 to 6 the volume doesn't increase, but actually drops slightly. From 6 to 9 the volume increases but after 9 the volume drops quickly to nothing.

i believe I have everything wired correctly per your schematic and the pot is a 1meg, audio tapper, R31 is pulled and R16 was replaced with a 1meg.

Any thoughts?

thanks!

[jim p]

The solution would be to add a resistor in series with the control grid of the EL84 or a minimum value of resistance in series with the master volume pot. The idea of the master volume pot is to use the existing volume pot as a gain pot to overdrive the second triode for preamp overdrive then use the master volume pot to limit the signal to the output tube. So you would normally not turn the master volume pot up past ½ to ¾. If you want to allow for the master volume pot to be turned to maximum you will need to add a resistor in series with the pot to the coupling cap C7 say 50k to 100k ohms to set a limit. The way it is now if you turn the pot to maximum on the positive going signal to the control grid of the EL84 if the amplititude is high enough you will get grid current from the EL84 that will look like a low impedance to the 12AX7 driving it and it will not be able to supply that through R6. But as I said you should limit the master volume to ¾ max and use the gain pot to increase the volume if that is not enough.

As you change the volume the load on the 12AX7 is changing at the high volume settings this reduces the gain of the 12AX7 and the loss of signal when you set the master volume pot at a high level.

So basically you need to supply enough signal to the master volume pot by where you set the gain pot so it has something to work with. Every pot in the amplifier tone, gain and master volume are killing signal when you turn them down and what the master volume pot has to work with is dependent on what is before it that is the tone and gain pot settings.

To give you a better idea of what I am talking about check out this article.
http://www.tgpwebzine.com/?page_id=808

[jim p]

Some people have stated that the Crate V5 is a little boxy sound wise. In an early post I showed a beam blocker to reduce this and cut down on the ice pick tone from the speaker. Since then I have run across this article http://www.tgpwebzine.com/?page_id=424 and this looks like it may make for a better solution. They talk about reflections of the sound back to the speaker with a beam blocker which is something I thought might be a problem when I tried it. What is neat is this creates the effect in a way of a dual cone speaker by blocking the outer part of the cone from emitting sound at higher frequencies. The higher frequency signal from a 10 inch speaker are not as pure a tone as the lower frequency sounds. By physics from what I have found in other articles the frequency range of a speaker is relative to the cone diameter divided into the speed of sound and a factor of ten greater in frequency from that point. So for a 10 inch speaker this is 13584 inches/sec divided by 10 inches for 1358 Hz to 138 Hz so all those frequencies above 1358 Hz are less and less pure in tone. If you look at the response curve for 10 inch guitar speaker you can see some of this in the peaking of the curve at higher frequencies.

Anyway food for thought and maybe something you may want to try out.

[SciHi]

Any thoughts?

I posted this earlier: http://www.thefret.net/showpost.php?p=140280&postcount=261
Maybe a litttle more conventional SE master volume and it worked great. I know Jim has had the discussion earlier about the grid resistor before or after the pot (or grid load), but after the pot is a little more conventional. Does it make any difference? I don't really know but the 250K pot with 6.8k grid resistor, post pot, sure added a lot to my amp. I did a half dozen other mods that didn't last as long as it took to put them on, but this master volume on my v5 is a real keeper.

[stoneattic]

jim_p, I tried the 100k resistor in series with the pot as you show on the schematic but have essentially the same issue. The control seems a little better but it still drops to nothing above 9 or so and there's still the dead spot/drop though the middle of the sweep.

SciHi, on your schematic there are a few other mods. Is the only thing relevant to the MV mod the pot and resistor shown in blue?

[jim p]

Looking at the markup I posted and doing some calculation if you still have C3 installed remove it. As you turn the pot up the capacitor could be working against you.
Also it may pay to check the pot with an ohmmeter sometimes they go bad where either the wiper looses contact to the resistive element or they wrap around and connect to the lower side which is ground in how this pot is wired.

The more I think about this the more I think your problem may be the pot is bad. I do think the 220p cap can work against you so it may be best to remove it. But as far as grid current that should not happen until full volume out of the amplifier so I think I was wrong on my earlier post. It is probably a good idea to add a series resistor with the pot but I thought I would make the mod as simple as possible. As far as how I marked up the first schematic it is the same as the master volume mod for the Valve Jr over at the Sewatt web site with exception of pot value which is 250k on the Vj mod. But higher value pot will give you greater gain from the 12AX7 driving the EL84 so that is why I suggested 500k to 1 Meg. As far as a grid resistor the pot is a resistor in series with the grid and connected to ground so you could add one but no real need.

[SciHi]

SciHi, on your schematic there are a few other mods. Is the only thing relevant to the MV mod the pot and resistor shown in blue?

That is correct. The other mods are for other reasons...

[stoneattic]

jim_p, I pulled C3 but the only difference it made is that now the volume change from 0-4 is minimal, and the volume change from 6-9 is more dramatic. It still drops to nothing from 9-10 and there's still the dip in volume from 4-6, but it's not quite as noticeable, which could just be because the overall volume is lower at 4 now.

[jim p]

jim_p, I pulled C3 but the only difference it made is that now the volume change from 0-4 is minimal, and the volume change from 6-9 is more dramatic. It still drops to nothing from 9-10 and there's still the dip in volume from 4-6, but it's not quite as noticeable, which could just be because the overall volume is lower at 4 now.

Have you tried checking the pot with an ohmmeter? The overall circuit is pretty basic and as far as others posted main difference is the value of the pot used. Just to check R16 the 220k resistor has been removed, yes? If not it should be. Another thing I noticed is that for some reason R6 in the schematic looks like it is 10k but it should be the stock value of 100k just in case you thought that was a change you needed to make. Have no idea how the screen shot made that come out that way. So if you ohmmeter the wiper of the pot to ground with power off of course should be 100k at the mid point to 1 Meg ohm at full clockwise position and should be the opposite if you test the C7 100k ohm resistor side 1 meg at full counter clockwise to zero ohms at full clockwise. Hope this helps.

[stoneattic]

Have you tried checking the pot with an ohmmeter? The overall circuit is pretty basic and as far as others posted main difference is the value of the pot used. Just to check R16 the 220k resistor has been removed, yes? If not it should be. Another thing I noticed is that for some reason R6 in the schematic looks like it is 10k but it should be the stock value of 100k just in case you thought that was a change you needed to make. Have no idea how the screen shot made that come out that way. So if you ohmmeter the wiper of the pot to ground with power off of course should be 100k at the mid point to 1 Meg ohm at full clockwise position and should be the opposite if you test the C7 100k ohm resistor side 1 meg at full counter clockwise to zero ohms at full clockwise. Hope this helps.

And the big d'oh, take his soldering iron away, award goes to me.
I had the screen grid and ground connections reversed on the pot. :thwap:

Thanks again for all your help and patience. I'm thrilled with this little living room practice amp right now. For want I plan on using this for it's perfect. I still have the VVR to add to it but honestly if I had done the MV first I may not have bothered ordering the VVR but since it's sitting here I'm going to (try to) install it.

[jim p]

Glad you have the master volume all sorted out and it is working. Figured there should be no problem but have not done the mod myself and I have been fooled by electronics before. Up side tubes take more abuse then transistors and FETs so they are more forgiving when you make a mistake.

If you have not done the variable voltage regulator mod yet just have a question on supplied hardware. I think you got a mica washer with that to isolate the tab of the T0220 FET from the chassis but did they supply thermal compound, a shoulder washer, metal screw and nut. Over at Sewatt someone was asking about chassis mounting and they were talking about a nylon screw and nut. Nylon is not good because it expands with heat and from thermal cycling and can loosen so you loose thermal contact also FET could move and short. Thermal compound will make for better thermal contact of the FET to the heat sink so it helps to use it for best thermal connection. Anyway over at Sewatt he posted that he got the shoulder washer from someplace so you could look over there to find where if you need one.

[stoneattic]

Glad you have the master volume all sorted out and it is working. Figured there should be no problem but have not done the mod myself and I have been fooled before by electronics before. Up side tubes take more abuse then transistors and FETs so they are more forgiving when you make a mistake.

If you have not done the variable voltage regulator mod yet just have a question on supplied hardware. I think you got a mica washer with that to isolate the tab of the T0220 FET from the chassis but did they supply thermal compound, a shoulder washer, metal screw and nut. Over at Sewatt someone was asking about chassis mounting and they were talking about a nylon screw and nut. Nylon is not good because it expands with heat and from thermal cycling and can loosen so you loose thermal contact also FET could move and short. Thermal compound will make for better thermal contact of the FET to the heat sink so it helps to use it for best thermal connection. Anyway over at Sewatt he posted that he got the shoulder washer from someplace so you could look over there to find where if you need one.

You are correct about the mica washer, but there was no compound or fastener hardware. I had planned on using compound though. But I'm really glad you mentioned using a shoulder washer. I would have just used a standard screw. When I saw the mica washer I realized that it needed to be electrically isolated but (mistakenly I guess) assumed that the hole was isolated. I have to dig though my random electronics hardware to see if I have an appropriate shoulder washer.

Due to the layout/location of where I plan to mount the VVR it doesn't look like I can mount the FET directly to the chassis. (I put the MV in place of the power indicator light and plan to mount the VVR in place of the on/off switch. I think relocating the on/off switch and light would look cleaner.) I had plan on mounting the VVR to a pretty large (relatively speaking) aluminum heat sink I have laying around which would be mounted to the chassis. Do you see any problem with this? The VVR is good for 50W so I don't think it's going to generate too much heat with this little 5W amp. Plus the heat sink is large in relation to the heat sink. I can take a pic of the sink I plan to use with the FET if you think it would help.

[jim p]

As far as the heat sink you will require as a guess figure you have 360 volts on one side of the FET and you dial the source of the FET to say 120 volts so you would have 240 volts across the FET. Figure the current that the tube is operating at will drop to say 25mA so the FET will have 240volts at 25mA for approx 6 watts. The maximum temperature the FET can operate at is 150 degrees C figure the amp is running hot at 40 C so can allow for a 110 degree C rise for the FET so you need a heat sink that can do 110C/6 watts or 18C/ watt or lower. So if you know the spec for the heat sink you are going to use or can find it or one that looks like it that should give you a good idea if what you have will work (look at heat sinks at Mouser electronics or Digi-Key). As I said the actual power on the FET is a guess. Looks like a TO 220 FET can do maybe 2 watts at 20c ambient temperature without a heat sink power greater then that will require a heat sink. Also air flow helps and you will have this in a box so you want to derate things a bit for that. I also left out the junction to case loss for the FET but looks like it should be just around 5 C so?

Probably best to get everything working run the amp for awhile and see how hot the heat sink gets before you button it up.

[jim p]

I was just surfing around and found Musicians Friend has the Crate V5 at 99 bucks with 10 bucks for shipping. I thought they stopped making these amps?
http://guitars.musiciansfriend.com/product/Crate-V-Series-V5-5W-1x10-Tube-Guitar-Combo-Amp?sku=487050

I am starting to think this posting needs an index to help anyone who is checking it out for the first time. Or even looking for something they thought they saw.

[stoneattic]

jim_p, after Bill gave me a hard time I finally tried to finish the VVR install and ran into a few questions/issues:

1) You suggested replacing R26 with a 25K, the closest I could find is 24K. Is that okay?
2) You suggested replacing R18 with the 4.7K from R25 since R25 is now jumped. R18 is a 3W and R25 is a 1W. That seems like a problem, is it?

Thanks for your help.

[jim p]

The value of R26 is not too critical it is just a series dropping resistor to set the voltage of the plate supply for the 12AX7 so 24k is good. The wattage rating of the R18 resistor with 4.7k max current should be 15mA as the screen grid resistor the steady state current is around 4mA. As the volume out of the amp increases the current through that resistor will rise as a percentage of the plate current I think a 1 watt will be OK but if you have a 2 to 3 watt 4.7k go ahead and use the higher wattage.

[stoneattic]

Thanks again jim_p.

I would have to order a higher wattage resistor so I'll go ahead and put the 1W in there for now. Next time I'm placing an order I'll pick up a 3W to replace it.

I'm not going to be playing this amp at high volume anyway. It's meant to be my living room practice amp. I have other amps for loud time. :)

[jim p]

Thought I would post a different variable voltage regulator that uses two shunt voltage regulators to produce current sources with two n-channel mosfets. The current source at the ground side subtracts current from the high side current source to reduce the current across a resistor attached to the gate of the pass mosfet T2 for voltage regulation. Less current through the resistor R2 equals lower voltage on the output of the regulator. With this the adjustment pot has only 2.5 volts across it instead of over 300 volts so figure this is a little safer. The use of the TL431 ICs as current sources should reduce the ripple voltage of the power supply for a quieter amplifier. Bypass caps can be added to the gate of the pass mosfet T2 in the schematic a 1uf cap is equal to an approx 100 reduction in ripple voltage. The FETs FDP7N50 cost 70 cents each at Mouser and the TL431 goes for 39 cents each.

There is no current limiting in this circuit with two more resistors and another TL431 a precise current limit could be added.

Another variable voltage regulator circuit uses zener diodes and the TL431 to control the output voltage of the pass mosfet. The TL431 is used as an adjustable current sink to set the voltage of the output by the voltage dropped across R1. The zener diodes are rated at 5 watts one a 160volt the other a 180 volt other values can be used the value of R2 3.3k may need to be changed if a much lower zener voltage is used.

[jim p]

This is a variable voltage regulator circuit that uses zener diodes and the TL431 to control the output voltage of the pass mosfet. The TL431 is used as an adjustable current sink to set the voltage of the output by the voltage dropped across R1. The zener diodes are rated at 5 watts one a 160volt the other a 180 volt other values can be used the value of R2 3.3k may need to be changed if a much lower zener voltage is used. With this circuit there is just 2.5 volts across the adjustment pot. The current limit is set by the value of R3 the 25 ohm resistor for a limit of 100mA. The current limit can be adjusted with a different value resistor based on the 2.5 volts at the reference pin of the TL431 so 2.5 volts divided by current limit equal to resistor value to use. In simulation I got a ripple rejection ratio of 200 or -46db. On the parts front the FDP7N50 mosfets are 70 cents each at Mouser the TL431 shunt regulator is 30 cents at mouser a 400 volt 1 uf film cap can be used at the gate of the pass mosfet. The current sink mosfet T3 needs no heat sink. If you use a heat sink instead of the chassis for the pass mosfet T2 you will need a 10 C/watt or better heat sink(lower is better say 8C/Watt).
Using the zener diodes maintains voltage regulation as the raw power supply voltage rises due to lighter current load. Also the adjustment pot has only 2.5 volts across it for a bit better safety. The TL431 provides a precise current limit along with the value of R3 used.
Of the three circuits this one gives the best ripple rejection so it would probably be the best to use. I would get a few zener diodes to try different total voltage value relative to the raw supply they are around 30 cents each so? Also have added the current limit may want to consider playing with the current limit range so might want to get a few low resistance values if you don’t already have them.

[jim p]

For those of you thinking about using an L-pad as an attenuator I was looking into how to make the L-pad look more like a speaker to the amplifier. If you look at the impedance curve that you can find at Jensen Speakers or Eminence speakers on the average an 8 ohm speaker looks like approx 6 ohms in series with the average value of an 800uH choke. While an L-pad is two pots one in series with the speaker and one in parallel so it looks like a resistor. With the speaker at approx 800Hz the inductance starts to dominate and the impedance continues to rise to approx 50 ohms at 20 kHz. With the impedance curve you will see a sharp rise in impedance at approx 70 to 110 Hz that is the resonance of the speaker which I cannot duplicate with the L-pad but the high frequency curve can be matched to approx 3 kHz. To do this you need to use an L-pad twice the impedance you want to have for a load so that is 16 ohms for an 8 ohm load and an 8 ohm L-pad for a 4 ohm load. With the 16 ohm L-pad you will need to parallel it with a 12 ohm 10 watt resistor in series with a 1.5mH choke rated for 2 amps then connect the speaker to the normal terminals on the L-pad this looks like an 8 ohm speaker to the amp. The 8 ohm L-pad needs a 5 ohm 10 watt resistor with a 1.5mH 2 amp choke in series in parallel this looks like 4 ohms to the amp. This should get the L-pad sounding closer to speaker at high output levels. I did not look into the resistor price but for the inductor two 820uH chokes in series can be used for the 1.5 mH and they are 2.60 each at Mouser.

[stoneattic]

I finally finished the VVR install and figured I'd give a little update on what I did. The mods I made are:

1. Removed the IC in the pre-amp and modified the tone control per jim_p's post
2. Added a Master Volume per jim_p's post
3. Installed the Hall Amplification VVR to control the voltage to the power tube only (installed it per jim_p's post)
4. Replaced that abomination of a speaker with a Jensen MOD 10-35.

The attached pics show:
1. The controls were I installed the Master Volume in place of the original power indicator light and the VVR in place of the original power switch and installed a smaller LED power indicator.
2. The circuit mods.
3. Relocating the power switch to the back, underneath (you can see the VVR board as well)

I made a few mistakes along the way that I had to fix and I'm not proud of the way some of the work looks but the results are amazing. I play a pretty wide range of music, classic rock, 80s, grunge, etc, and I can get plenty of sounds/tones/levels of gain with the mods and additions of the MV and VVR. I can go from pristine clean to a really nice crunch.

The MOD 10 sounds great. It's really hard to beat for the money (I got it from music123 for $34.80 shipped).

I couldn't be happier with the way this turned out sound-wise, especially for the money I have into it (about $115 total, including the amp which I picked up used for $40).

Many thanks to jim_p! :dude:

[Bilsdragon]

Sweet!!! Now you can help me with the suggestions Jim gave me for the champion 600.:bravo:

[stoneattic]

Sweet!!! Now you can help me with the suggestions Jim gave me for the champion 600.:bravo:

Not a chance!!!!


Just kidding of course, whenever you're ready to go crazy with the soldering iron let me know.

I'll bring the V5 in on Monday and let you check it out.

[jim p]

The autotransformer volume control is a bad thing to connect to a tube amplifier as you lower the volume thus increase the ratio between input from amp and speaker the reflected impedance will rise. These volume controls are fine for a solid state amp that will have problems with low impedance loads but no problem at all with a high impedance load. Most even have the capability to raise the impedance by a factor of two to four for putting speakers in parallel. What happens at a low volume setting it might look like you have 2 k ohms or more connected to the output of the amplifier which might kill the output transformer or power tube on your tube amp. But if we put a simulated speaker load of 6.5 ohms with a 800uH to 2 mH choke in series (equal to an 8 ohm speaker) in parallel with the autotransformer this will be as close to looking like driving a speaker with a roll your own attenuator as you can get. The high reflected impedance of the autotransformer will have little effect on the simulated speaker load so to the amp it will be like driving a speaker.
If you build this you want to make sure the resistor and inductor load will always be connected when using the autotransformer. You should have the ability to totally by pass it for driving the speaker directly. For the inductance of the speaker load if you use two to three inductors for the maximum value of inductance you can connect switches across then to short them out, with all in being bright to all out being bass or flat in response.
One thing left out of the simulated load is the resonance response of a speaker this can be simulated with an inductor in parallel with a resistor and capacitor, but fell the low frequency response is not the most important to simulate. Also the resonance is actually the fact that the speaker coil is similar to a motor and a motor can also be a generator. What happens is related to the rebound of the speaker surround and how the speaker is mounted if in an open cabinet, closed back cabinet or ported cabinet as the speaker returns to it natural position it produces a current close to equal to the current needed to produce the tone and amplititude it was driven to. Thus it looks like little current is required to drive the speaker at the resonant frequency so it is a high impedance point in the frequency versus impedance curve.
For the chokes the J.W. Miller (Bourns) series 2300HT or 2300 have values in the range required and good current capability both Digi-Key and Mouser carry them. The volume controls can be found at Parts Express. For the watt wasting resistor the wattage required should be twice the wattage of the amp you are going to hook up to so for V5 minimum of 10 watts.

Tried to include a speaker response curve but was cropped down to be of little value.

Just as a final point on attenuators you are maxing out the output power of the amp so if anything is marginal it might fail with heavy use such as the output transformer. Also your output tube life might be shortened from heavy use. I did see one attenuator that states it is a 30 ohm load and this makes it safer to use but I am not so sure that should be the case. High impedance loads lead to high flyback voltages in the amp which is what causes arc voltages that cause breakdown so not sure this is valid.

[rjohnj]

Hello all....
Firstly, I am new to the forum and initially came here researching from this thread to mod my v5.
I mainly play strats and mainly blues and classic rock and was just after a good litle tube amp for practicing at home and hopefully that was loud enought to jam with friends.
I hope that you aren't all sick to death of going over this now but I am in need of some assistance please.
My first mod was the speaker - changed to an eminence ragin cajun. Then replaced the the tubes with JJ's. Swapping out the 12ax7 with an at7.
Before I touched the circuitry the amp didn't sound too bad. It was nice and clear, not overly loud, but it was a little harsh on the highs. Not bad for blues but was enticed into doing the mod given what everyone was saying about the improvement in tone. I also wanted to have a pure tube amp and had not done any mod's to an amp before and figured this was a good place to start.
So here's where I am at now......
I read some good reviews of deafelectromarks mod and it seemed easy enough so I followed it as best I could. I am not a tech person but as long as I have instructions I can do most all things. (Modding amps is the next step up for me after building guitars and modding pedals). Given my lack of technical understanding I found the instructions a little vague but think I completed all parts of the mod as indicated.
My problem is that I don't think I've achieved the results that I think I should have. Main reason being is that I think, if anything, the amp is now quieter (as in less loud) than when I started with very little breakup at full volume. There is no way you could play with a band, even if they played quietly and the amp is on full. I think my little micro cube is louder. I haven't yet touched the tone stack and at the moment it sounds dull and is very much lacking in highs. But my main concern is first getting the op bypass mod right. Though would Jim P's tone stack for op-amp bypass modded circuits work with deafelectro's mod?
I have attached a pic of both the front and back of the circuit board (no schematic - I'm sure I'd draw it up wrong) for you to see what I have done. So, if you are familiar with this mod or have done it yourself can you please let me know if I have done something wrong.

These are the instructions I was following:
*************
Begin by cutting the trace after the input jack leaving R10,R11 for input loading. This will be just before pin 3 of op amp.
Run a short length of coax from there to pin 7 of the 12AX7, and ground this wire at only one end (to prevent ground loops).
You will be cutting the volume pot out of the circuit and reroute wires as follows-keep the tone control circuit for now).
Connect the middle wiper to pin 2 of 12AX7. Cut out the R7, 220K resistor and the pot will take it's place for the load and volume control BETWEEN the two 12AX7 halves.
Connect the top of the control to the junction of R15, R29,and C28:
and the bottom to ground.
Cut out the 100K (R15) (or R27, 10K) Resistor(s) so that the second half of the preamp tube is driving the same load. So you are basically removing R15, R27 and R7.
**************
nb. I removed the op-amp though I know I really didn't need to.
nb. I used jumper wire instead of co-ax after a later post said it wasn't really required.

Help please!
Thanks in advance.
rhohnj (Ryan)

[jim p]

Looking at the picture of the top of the board looks like you may have some parts loading down the input signal. I think you should remove C25 and R1 then you would be better off with the jumper going to the junction of C25 and R2 keeping R1 in series with the control grid. I attached a marked up schematic.
I don’t like the stock tone control find the dark to bright to dark way it functions to be odd. One problem with taking out the op amp is you have no treble boost without it, so the tone control just becomes a treble cut instead of a boost and treble cut.
A way to get a boost back is to change C1 to a 220nF capacitor if that is too bright you can split the cathode resistor R3 into two 750 ohm resistors in series with 2.2uf across one resistor and 440nf across the other resistor.
If you are after maximum volume from the amplifier a 16 ohm speaker is your best choice due to the 20:1 turns ratio of the output transformer.
Also you may want to go back to a 12AX7 as the preamp tube to see what effect that has.

[rjohnj]

thanks Jim
I will try this and see how I go but if anyone else has other views I'd still love to hear their thoughts too.
Though I will stick with the current 8ohm speaker given I just bought it.
Your previous posts and this response is much appreciated.
cheers
Ryan

[rjohnj]

Ok, I got some pictures of deafelectromark's mod and so, I think I finally have it how he did the mod on the schematic and his pictures of the board.

http://i29.photobucket.com/albums/c257/t_achin/guitar/TopofV5.jpg
http://i29.photobucket.com/albums/c257/t_achin/guitar/V5othersidewithquestionsanddrawninw.jpg
http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticmodv23.jpg


Hi Tim
Looking at your pics there seems to be some parts removed not detailed in deafelectro's mod instructions. (D9, D10, R28, R1, C27) and also cut the trace between R28 and R29.
Is this something youcame up with yourself? What effect did it have?
cheers
Ryan

[jim p]

There is a cut needed not shown in the schematic above. You need to cut the wiper of the pot free from ground. I think this has come up before.

[rjohnj]

Looking at the picture of the top of the board looks like you may have some parts loading down the input signal. I think you should remove C25 and R1 then you would be better off with the jumper going to the junction of C25 and R2 keeping R1 in series with the control grid. I attached a marked up schematic.
I don’t like the stock tone control find the dark to bright to dark way it functions to be odd. One problem with taking out the op amp is you have no treble boost without it, so the tone control just becomes a treble cut instead of a boost and treble cut.
A way to get a boost back is to change C1 to a 220nF capacitor if that is too bright you can split the cathode resistor R3 into two 750 ohm resistors in series with 2.2uf across one resistor and 440nf across the other resistor.
If you are after maximum volume from the amplifier a 16 ohm speaker is your best choice due to the 20:1 turns ratio of the output transformer.
Also you may want to go back to a 12AX7 as the preamp tube to see what effect that has.

Hi again Jim - sorry, hope you're not sick of me yet.... just want to clarify a couple of things.
I performed the simple mod you suggested, pulling out R2 and C25 and moving the jumper to between them. Well I definitely got an increase in output volume (and tube break-up) - thanks again!
I haven't yet boosted the treble as I need to get to the store to get a 220nf capacitor.
So.... I am hoping, but don't know yet, if that will fix my current problem which is that it gets very 'farty' when you plug in humbuckers. It's not too bad with single coils (but has lost the tightness in the bottom end I had pre-mod) - do you think the 'fartiness' will go away with an increase in the treble from the change in cap at C1? Or do I need to modify something else?

Also, you were nice enough to mark up a correct shematic (in last post) for the similar, but more extensive mod that Timothymegg originally posted. This mod had further components and traces removed. Do you know if that would yield a different result to what I currently have? What are those extra pieces doing (R1, D9, D10, R28, C27)? Just in case it helps I wouldn't mind getting back a little bit of fender into this amp that has quickly turned very marshall-ish.

On another note... I just pulled apart an old 70's 70watt hi-fi amp for parts. It's got a nice big sansui power transformer. How do you think this would go if I used it in a guitar amp???

thanks!!!!

Ryan

[jim p]

Removing D9 and D10 will make no real difference they were in there to protect the op amp but have no real effect on the input signal. Having R1 in series with the control grid of the tube will help roll off high frequencies when you overdrive the input tube and help keep radio interference down. Taking out R28 and C57 may take them out of circuit with the volume pot mod so probably a good thing to do.
For more of a Fender tone should consider adding feedback look through the previous posts and you should find it as a mod already described.
If it is a 70 watt solid state transformer it would only be useful for a 70 watt state amp, probably good for plus and minus 40 to 45 volt supplies so of no use with tubes.

On the feedback look at the post "Adding a presence control (feedback) to the V5"

[jim p]

This is a good article on cathode biasing and setting up the DC bias for the tone you want. http://www.freewebs.com/valvewizard1/Common_Gain_Stage.pdf
For the most part it is how the tube responds to overdrive so the tube to play with would be the second triode on an amp with the master volume mod. I have posted a schematic that uses mosfets to parallel the highest bias resistor value to set the DC bias for different tones. The first bias rock will have the tube cold biased so it will clip at cutoff (no current flow). Pulling in the first switch Jazz will center bias the tube for the most head room so not intended for clipping. The second switch Blues will hot bias the tube so it will clip at saturation where the control grid starts to conduct. The mosfets can be turned on by the DC heater voltage and will keep the ground loop close to the tube for minimum noise. You can also just go with a fixed bias equal to 10k to 5k for Rock, 2.2k to 1.2k for Jazz and 750 to 500 ohms for Blues bias.
Also attached a load line equal to 100k plate resistor with 250 volt plate supply to show where some of these bias values fall on the load line.

[rjohnj]

This is a good article on cathode biasing and setting up the DC bias for the tone you want. http://www.freewebs.com/valvewizard1/Common_Gain_Stage.pdf
For the most part it is how the tube responds to overdrive so the tube to play with would be the second triode on an amp with the master volume mod. I have posted a schematic that uses mosfets to parallel the highest bias resistor value to set the DC bias for different tones. The first bias rock will have the tube cold biased so it will clip at cutoff (no current flow). Pulling in the first switch Jazz will center bias the tube for the most head room so not intended for clipping. The second switch Blues will hot bias the tube so it will clip at saturation where the control grid starts to conduct. The mosfets can be turned on by the DC heater voltage and will keep the ground loop close to the tube for minimum noise. You can also just go with a fixed bias equal to 10k to 5k for Rock, 2.2k to 1.2k for Jazz and 750 to 500 ohms for Blues bias.
Also attached a load line equal to 100k plate resistor with 250 volt plate supply to show where some of these bias values fall on the load line.

Wow.. I think you read my mind. I was researching biasing throughout this thread last night.
I have done all of my modding except for the bias which causes me some clipping from when the amp is cranked and heavily over driven.
My other mods have left my amp sounding awesome. Thanks again for your assistance.
After my initial low volume problem, as recommended, I have since removed C25, R2, put back in R1 and jumped to R2, C25 junction - solved volume problem. Then removed D9, D10, R28 and C27, cut C14/C28 trace and swapped out C1 for a 470nf. I didn't have a 220nf, but it sounded great so I kept it. Then after pulling out C5 I got a little more sparkle. The wiring is now all much neater and the sounds is truly great - no need for the feedback mod, I got back all the crystal clear top end that I was after.

So now I am thinking I might just put in a master volume and definitely need to do something about the bias. I still need to do some homework on this to understand the theory better but do i need to first tackle the screen grid voltage or do I just need to worry about finding the right resistor to add in parrallel with the already existing 330ohm R17? (I have a 12AT7 in there).
And does the added resistor in parrallel need to be 2 watt or great if added in parrallel given there is already a 5 watter in there?

And not than I am not happy because this is just a little 5 watt, 10inch practice amp but is there a way to thicken up the bottom end a little?

Ryan

[jim p]

I am a little confused on your post you talk about R17 and the triode at the same time R17 is the cathode resistor for the EL84. I am trying to check what I had as a final value and it looks like 270 ohms, but it is best to use a voltmeter and check plate voltage and cathode voltage to calculate the power dissipated by the tube when making these changes. Not sure I covered amplifier output tube bias in this thread if you go to Sewatt on the Valve Jr page you can find it there. If you do parallel R17 to get say 270 ohms with a 1.5k the 1.5k can be a 1 to 2 watt resistor.
On the bass response end one big limit to the stock bass response of the amplifier was the capacitor values used in the op amp circuit, you now have that bypassed. I know I posted what I found for bass response and it is as good as it gets on this amp especially with the 20:1 turns ratio and an 8 ohm speaker. So even if you changed the output transformer I doubt you would do much better.

[rjohnj]

I am a little confused on your post you talk about R17 and the triode at the same time R17 is the cathode resistor for the EL84. I am trying to check what I had as a final value and it looks like 270 ohms, but it is best to use a voltmeter and check plate voltage and cathode voltage to calculate the power dissipated by the tube when making these changes. Not sure I covered amplifier output tube bias in this thread if you go to Sewatt on the Valve Jr page you can find it there. If you do parallel R17 to get say 270 ohms with a 1.5k the 1.5k can be a 1 to 2 watt resistor.
On the bass response end one big limit to the stock bass response of the amplifier was the capacitor values used in the op amp circuit, you now have that bypassed. I know I posted what I found for bass response and it is as good as it gets on this amp especially with the 20:1 turns ratio and an 8 ohm speaker. So even if you changed the output transformer I doubt you would do much better.
sorry, i've probably confused you a little because i'm still learning all this.... the past week has been a steep learning curve for me. I will definitely try to learn the theory in the next few days for the most appropriate way to deal with the the bias. (I have a bias measurement tool on the way as well).
thx

[schenkadere]

Aside from the obvious speaker change and tube change, which I did with a Warehouse Veteren and JJ's, what is the simplest mod to get this amp sounding even better? And...do any of you guys do this work? I'm a soldering spaz.:)

[jim p]

Look at post #168 this takes the op amp out for an all tube amp.

[rjohnj]

Look at post #168 this takes the op amp out for an all tube amp.

I've completed all my mods and the amp sounds great - better than anything else in it's class, except for one thing..... when I have the amp and guitar cranked and hit the E-string or power chord (especially on the neck pickup) the amp gets really 'farty'.
I've messed with the bias and measured all my voltages and if I keep it in the 'healthy' range it still gets farty. I've tried running it really hot and it seems to help but then the power tube red-plates. The standard 330 ohm cathode bias resistor actually seems to be about right to keep the amp within the recommended limits - it's even at the upper end of acceptable.Though I'm currently a touch hotter than that to help with the fartiness - 14v plate dissipation. Any recommendations on how I can solve this or do I just need to live with it?

Ryan

[jim p]

Just to check on your plate power dissipation calculations. You should have determined the cathode current then subtracted the screen grid current to obtain the plate current. Then the voltage across the tube which is plate voltage minus the cathode voltage is the voltage across the plate times the plate current for the power dissipation of the tube. The ball park number screen grid current is 4mA but there is a screen grid resistor you can measure the voltage across to get an exact number if you want.

No answer on the farty sound I would try driving another speaker if one is available to use.

[rjohnj]

Just to check on your plate power dissipation calculations. You should have determined the cathode current then subtracted the screen grid current to obtain the plate current. Then the voltage across the tube which is plate voltage minus the cathode voltage is the voltage across the plate times the plate current for the power dissipation of the tube. The ball park number screen grid current is 4mA but there is a screen grid resistor you can measure the voltage across to get an exact number if you want.

No answer on the farty sound I would try driving another speaker if one is available to use.

without rechecking, i think, I had something like 319 volts between plate and cathode (taken from pin 7 to 3), 11 volts for the cathode resistor. That's with 250 ohms resistance. (screen is estimation).
then i plugged my numbers into the tool below to get my plate dissipation (and to save me doing the sums)
http://www.webervst.com/tubes1/calcbias.htm
I might try plugging through my 1x12 cab and see what happens.

[jim p]

It looks like the Weber calculator allows just 2mA for the screen maybe just being conservative. Going by the 11 volts on the cathode if you had a 270 ohm resistor and the voltage stays at 11 volts your cathode current would be 41ma so would be just about bang on 12 watts on the plate ( 319 volts times 38mA = 12.1 watts)

[rjohnj]

It looks like the Weber calculator allows just 2mA for the screen maybe just being conservative. Going by the 11 volts on the cathode if you had a 270 ohm resistor and the voltage stays at 11 volts your cathode current would be 41ma so would be just about bang on 12 watts on the plate ( 319 volts times 38mA = 12.1 watts)

yeah that's pretty much what I got just pushing the boundaries slightly with 250 ohms to help with the sound a little.
Not sure why I have to run it so hot to get rid of the 'farting' though. 100ohm resistor sounded good but just ran the tube too hot.

[SciHi]

...get rid of the 'farting' ...

I have found that the v1a cathode bypass cap and/or first coupling cap control the flabby bass. For HBs I have used either 0.68 or 1 uF cathode bypass caps, you can go a little higher with single coils, ~2uF. Or use a real small coupling cap, like the vj fender/voxy mod value, 0.0022uF, my v5 has a 0.0047uF coupling cap. I am using 10K R1, added a master volume with 6.8K grid resistor after the mv, and did the screen resistor mod to the el84. My tone stack sucks lots of gain so the amp is very clean and very tight bass but still retains the thick tone. I also tried adding the nfb but it was too thin with my setup. My speaker is also a thick cone Celestion Tube 10 (G10E-30), and doesn't breakup even playing a bass through the amp. I suggest you try to figure out if it is the amp or speaker that is causing the "farting."

Rock_Mumbles posted this on his tech site "zaphod_phil Quote:
I think the moral of the story is to either use a smallish cathode cap (below 100uF) and bias fairly hot with a low cathode resistor value, or use a very large cathode cap (1000uF to 2200uF) and bias cooler with a larger resistor value. In between values will usually sound woofy."

found here:
http://www.18watt.com/modules.php?name=Forums&file=viewtopic&t=17468&postdays=0&postorder=asc&start=15

So maybe as you change the el84 cathode resistor value, you need to change the cap value?

[jim p]

One thing to keep in mind as you lower the value of coupling caps and bypass caps you are reducing the bass response. So you may just be eliminating the problem by having less bass, ok if the bass response is not important to you. One thing to search out on the web for is blocking distortion you do reduce this by reducing the value of coupling caps but you can also reduce the value of the grid resistor on the control grid of the tube to reduce it.
When you bias hot by reducing the cathode resistor value what may be the reason for better response is the RC time constant (resistance times capacitance) of the cathode bypass capacitor and cathode resistor is reduced. The cathode of the output tube shifts its DC value when driven hard and the recovery time could be a function of the bypass capacitor used. So instead of biasing the tube hot maybe you should try changing C9 to a lower value by calculation you could go as low as 10uf with a cathode resistor value of 270 ohms.

[rjohnj]

One thing to keep in mind as you lower the value of coupling caps and bypass caps you are reducing the bass response. So you may just be eliminating the problem by having less bass, ok if the bass response is not important to you. One thing to search out on the web for is blocking distortion you do reduce this by reducing the value of coupling caps but you can also reduce the value of the grid resistor on the control grid of the tube to reduce it.
When you bias hot by reducing the cathode resistor value what may be the reason for better response is the RC time constant (resistance times capacitance) of the cathode bypass capacitor and cathode resistor is reduced. The cathode of the output tube shifts its DC value when driven hard and the recovery time could be a function of the bypass capacitor used. So instead of biasing the tube hot maybe you should try changing C9 to a lower value by calculation you could go as low as 10uf with a cathode resistor value of 270 ohms.

great... I'll give that a go!
thanks
Ryan

[rjohnj]

One thing to keep in mind as you lower the value of coupling caps and bypass caps you are reducing the bass response. So you may just be eliminating the problem by having less bass, ok if the bass response is not important to you. One thing to search out on the web for is blocking distortion you do reduce this by reducing the value of coupling caps but you can also reduce the value of the grid resistor on the control grid of the tube to reduce it.
When you bias hot by reducing the cathode resistor value what may be the reason for better response is the RC time constant (resistance times capacitance) of the cathode bypass capacitor and cathode resistor is reduced. The cathode of the output tube shifts its DC value when driven hard and the recovery time could be a function of the bypass capacitor used. So instead of biasing the tube hot maybe you should try changing C9 to a lower value by calculation you could go as low as 10uf with a cathode resistor value of 270 ohms.

Well it looks like changing the bypass capacitor does do the trick. I didn't have a heap of caps at hand but tried a 33uf. Actually seemed worse but then switched to a 3.3uf and guess what, flabby bottom end gone!
Is 3.3uf too low? I still plan to experiment and I haven't yet checked my voltages etc... I don't know what impact this would have?
Also there was a 100volt cap in there and I only have a 50volt - is this okay here?
Thanks Jim and SciHi for the tips on this.

[jim p]

If you have 3.3uf across the 270 ohm cathode resistor that would be a bit low in value equal to -3db at 180Hz. Using 10uf will be -3db at 60 Hz. As far as voltage rating the voltage across the cathode is approx 12 volts max so a voltage rating of 20 volts or more is fine. The bypassing of the cathode resistor on a pentode probably has no big effect on the gain though so it may be no big deal. I need to look at this more to make sure but it is not the same as a triode.

Just checked and the cathode impedance of the EL84 is approx 88 ohms so not bypassing the 270 ohm resistor will drop the gain by about 75%

[rjohnj]

hi again all

Now that I am pretty happy with my amp I am just wondering about a couple of tweaks.
Can anyone tell me if I change R1 to a 1megohm (R2 is removed) if I will expect an increase in signal -and what impact would this have on gain?

What impact does changing the values of c3 or c4 have - can this help further tighten up the bottom end?

thx

Ryan

[chris2002rock]

The good news is that it looks like there are no SMDs on the board.

One thing I would check is the bias. If the schematic I have is correct, the cathode bias resistor is only 100 ohms. It seems like it should be bigger.

You will want to check the plate voltage as well.

What are you trying to accomplish by modding your amp?

tung

Where did you find a schematic for this amp?

FWIW, I am getting to the point where I might just replace the whole schematic with a hand-wired replacement. If possible, I wanted to just replace the tone stack (I doubt the solid state components are entirely to blame)...but I also believe the guy who said he replaced the entire circuit (save the tubes and transformers).

I was hoping for a glance at the schematic before I rip the guts out).

Thanks in advance for any help on this.

[SciHi]

Where did you find a schematic for this amp?


Right here: http://www.thefret.net/showpost.php?p=120172&postcount=28

[SciHi]

Can anyone tell me if I change R1 to a 1megohm (R2 is removed) if I will expect an increase in signal -and what impact would this have on gain?

What impact does changing the values of c3 or c4 have - can this help further tighten up the bottom end?

So what else did you do? I put R11 (1M) across the input jack, removed R10 and everything between it and R1 (including R2), so R1 is the input grid resistor which should be in the range of 68K - 10K in most peoples opinion. A 1 M should reduce signal.

I removed C3 but also moved the grid resistor (R31) after R16. C3 should drain some highs. C4 is part of the strange tone control, I reworked the tone control to a Marshall 18 watt normal channel tone control.

[rjohnj]

So what else did you do? I put R11 (1M) across the input jack, removed R10 and everything between it and R1 (including R2), so R1 is the input grid resistor which should be in the range of 68K - 10K in most peoples opinion. A 1 M should reduce signal.

I removed C3 but also moved the grid resistor (R31) after R16. C3 should drain some highs. C4 is part of the strange tone control, I reworked the tone control to a Marshall 18 watt normal channel tone control.


I've bypassed the opamp (jumpered d10 to r2/c25 junction to get to pin 7, top of vol pot to junction to junction of r15, r29 and c28, middle of vol pot to r27 to get to pin 2 and bottom of pot to grnd)
changed c1 to 1uf - after trying many values. Helps control the farty bottom end without getting too thin.
pulled out r2, r7, r15, d9, d10, r28, c27.
cathode resistor is 270ohm and bypass cap is 0.47uf - also best after trying many to help control flab in bass.
cut board at c27 to r28
Tried pulling C5 and lowering value but got to much treble.
Amp voltages are all okay and amp sounds quite marshall-ish (or more-so than a fender) and overall pretty nice. Break-up is not over the top but I was hoping for it to be a little louder. If it's on 5 it's a nice clean tone but too quiet.
speaker is now an eminence ragin cajun and tubes are jj's (at7 instead of ax7)

I've just put in the 1M resistor at r1 to try - i think it works?.. sounds fuller maybe?? it's definitely not louder which I was originally hoping for but not much quieter either, if any. Shoud I drop this back down?

I don't mind the tone control to add a little versatility.

what do your mods between input jack and r1 do?
any other suggestions??? louder and more sustain would be good. (nb.I know it's only 5watts)

[SciHi]

cathode resistor is 270ohm and bypass cap is 0.47uf - also best after trying many to help control flab in bass.

I wonder if you haven't cut some volume by too low of bypass cap value on the EL84. I know lifting the cathode bypass cap is like a 1/2 power switch, I think this is what JimP was getting at with his post. I actually went higher value on the EL84 bypass cap, you can get low voltage 220 or 470 uF at the Rat Shack. Higher values are described as tightening up the bass response, I believe more than cutting it. My personal preference is to cut or limit bass in the preamp, and tighten up bass in the power section. I did go with 1uF bypass caps on both preamp valves.

[rjohnj]

I wonder if you haven't cut some volume by too low of bypass cap value on the EL84. I know lifting the cathode bypass cap is like a 1/2 power switch, I think this is what JimP was getting at with his post. I actually went higher value on the EL84 bypass cap, you can get low voltage 220 or 470 uF at the Rat Shack. Higher values are described as tightening up the bass response, I believe more than cutting it. My personal preference is to cut or limit bass in the preamp, and tighten up bass in the power section. I did go with 1uF bypass caps on both preamp valves.

I don't think it's the bypass cap because I tried everything from 1000uf down to the 0.47 and the level was around the same. Maybe it's about as loud as it gets?

I'm interested in the 1uf bypass caps on both preamps - what positions are these caps?

[jim p]

For what it is worth to get the maximum volume you should look into biasing the amplifier if you have not already. The other thing affecting the volume is the transformer having a 20:1 ratio which is more suited for a 16 ohm speaker then an 8 ohm speaker. So if you need the maximum power transfer out of the amplifier you need to either use a 16 ohm speaker or get a new output transformer. So that means spending 30 to 60 bucks for a new transformer or whatever the speaker will run you. For transformers there is Hammond 125 series, Edcor, OT8SE and OT10SE as a few choices. Look over the stuff at Sewatt web site for the Valve Jr to get an idea of the differences. On output transformers the higher the primary inductance the better the bass response but it is not specified in most cases so rule of thumb is the bigger and the heaver the better the bass.

[rjohnj]

For what it is worth to get the maximum volume you should look into biasing the amplifier if you have not already. The other thing affecting the volume is the transformer having a 20:1 ratio which is more suited for a 16 ohm speaker then an 8 ohm speaker. So if you need the maximum power transfer out of the amplifier you need to either use a 16 ohm speaker or get a new output transformer. So that means spending 30 to 60 bucks for a new transformer or whatever the speaker will run you. For transformers there is Hammond 125 series, Edcor, OT8SE and OT10SE as a few choices. Look over the stuff at Sewatt web site for the Valve Jr to get an idea of the differences. On output transformers the higher the primary inductance the better the bass response but it is not specified in most cases so rule of thumb is the bigger and the heaver the better the bass.

Yeah I don't think I'll be putting any more money into this thing. It's a good little practice amp as it is but I don't think it will ever get loud enought to gig with - unless it's mic'd up. Do you guys think yours are?
Also, to buy speakers and transformers over here (in Australia) is much more expensive than there.
I'll be heading to the UK on Monday for the next 6 months and can't take an amp anyhow - think I'll tackle a Tweed Twin build when I get home.

[SciHi]

Yeah I don't think I'll be putting any more money into this thing. It's a good little practice amp as it is but I don't think it will ever get loud enought to gig with - unless it's mic'd up. Do you guys think yours are?


I mic mine in church but only run the preamp gain on about 3 or 4.

I spend a lot of time on SEWATT valve junior forum, most of the technical discussions are relavent to the v5 or any single ended amp. Here is a quote from cGil in regards to the EL84 (discussion is about vj, C5 = C9 on v5);

"C5 is a bias bypass cap. This is required to get the max available power out of your tube. Go below the stock 25uF/35v, and you lose power. The bottom end tone will be softer and loose with the stock 25uF bypass cap. Depending on the speaker used, the bottom end can sound a bit flubby. Increasing this value makes the bottom end tighter. 1000uF/50v caps are very popular for tightening up a flabby bottom, but any value between 22uF and 2200uF will suffice." http://www.sewatt.com/comment/191746

VJ's come with 220R cathode resistor, the reverse problem to the v5. The 1000uF EL84 bypass cap is heavily used in various vj mods.

[SciHi]

I'm interested in the 1uf bypass caps on both preamps - what positions are these caps?

For the preamp v1a and v1b cathode bypass caps are C1 and C8, so I run both of these at 1uF on the v5. I have dark HBs (DiMarzio) and really need to keep a tight bottom end and use the coupling cap (C2) and tone stack to limit the bass/gain in the preamp. The tone stack reduces significant gain, so much that I never get any of the buzzy preamp overdrive even when dimed. I put in a master volume because I wanted the extra control, but mostly run the amp with low preamp gain setting and master volume dimed (maximum clean and EL84 chime).

I am really not interested in an OT upgrade either. I have used the amp through other speaker cabs, 1 and 2 12's, and it was a significant improvement. As jim stated on the OT, with a single 16 ohm Jensen Mod 12-70, the amp sounded particularly good. I already had a selection of speakers so it was no cost to try. I ended up with a Celestion Tube 10 in the v5, it was just best of what I had on hand that would fit into the cab. I have put little to nothing into the amp after the initial $79 purchase price (free shipping), I already had parts from other projects. Best investment in an amp I have made!

On others amps I have used 0.68uF cathode bypass caps on v1a. On my value junior I don't even have the v1b bypass cap, but I run it without a tone control. But on both amps I am running small coupling caps on v1a, 0.0047uF. I got a range of Mallory and orange drop (715, 716, 225s) caps from 0.001 to 0.0068uF to fine tune the amp to the guitar. I use mostly HBs so that is how I set up my amps. I have the split-single coil switch on my HBs so I can go to a thin "nfb like" rhythm tone.

A large group of us are all doing 5e3 builds (or vj conversions) from PPWATT. This was headed up by a fellow country man of yours, jamesrr, it is around 14 watts with 6v6's. You might want to check it out. (I may need to get a single coil tele for that amp!) http://www.ppwatt.com/node/16476

[SciHi]

tubes are jj's (at7 instead of ax7)

Missed this earlier, but many say that you should not use the 12at7 in preamp gain stage (designed for 12ax7), even more important in v1 position and with only one preamp tube. The 12ax7 may be too much gain, I would recommend going with 5751 if you want a lower gain tube (or reduce gain with tone stack/divider, etc). I think the 12at7 is a drive tube, used as PI, tremelo, or reverb, etc. It has a different current draw, bias, etc. Maybe Jim P or Rock_Mumbles can quote some of the specs on that tube. So put back in the 12ax7 and see how it sounds...

EDIT: OK, here is a data sheet on the 12at7; http://tubedata.milbert.com/sheets/093/1/12AT7.pdf

[rjohnj]

Missed this earlier, but many say that you should not use the 12at7 in preamp gain stage (designed for 12ax7), even more important in v1 position and with only one preamp tube. The 12ax7 may be too much gain, I would recommend going with 5751 if you want a lower gain tube (or reduce gain with tone stack/divider, etc). I think the 12at7 is a drive tube, used as PI, tremelo, or reverb, etc. It has a different current draw, bias, etc. Maybe Jim P or Rock_Mumbles can quote some of the specs on that tube. So put back in the 12ax7 and see how it sounds...

EDIT: OK, here is a data sheet on the 12at7; http://tubedata.milbert.com/sheets/093/1/12AT7.pdf

It may be due to poor quality tube as stock but the 12at7 sounds 10 times better. of course the ax7 is a little louder and has more gain but it is more brittle and colder sounding. the at7 is sooo much nicer, rounder and warmer. All my voltages and bias measurement is okay. Unfortunately I'm off overseas for a while in a day or so and can't take the amp to keep messing around with it so will have to wait til I get back. Though will try the 5751 - can't hurt.

[jim p]

Well being the Crate V5 has gone away here is a 99 buck tube amp with a bad speaker you can buy.
http://www.music123.com/Peavey-ValveKing-Royal-8--5W-1x8-Tube-Combo-Amp-481661-i1383113.Music123

[jim p]

Going back to the posts about farty bass sound and the cathode bypass capacitor value by this article http://www.aikenamps.com/Sag.html in the last paragraph about squish. It looks like the lowest value of bypass capacitor would be the way to correct this on the output tube. Also all the fixes you would use for blocking distortion lower value coupling caps or lower value grid resistors to lower the time constant if a DC shift occurs in the amplifier. The thing to note when you lower the coupling cap values or the grid resistor values you are also lowering the bass response.

On blocking distortion Aikens amps also has a posting on that you may want to check out.

[rjohnj]

Going back to the posts about farty bass sound and the cathode bypass capacitor value by this article http://www.aikenamps.com/Sag.html in the last paragraph about squish. It looks like the lowest value of bypass capacitor would be the way to correct this on the output tube. Also all the fixes you would use for blocking distortion lower value coupling caps or lower value grid resistors to lower the time constant if a DC shift occurs in the amplifier. The thing to note when you lower the coupling cap values or the grid resistor values you are also lowering the bass response.

On blocking distortion Aikens amps also has a posting on that you may want to check out.

hmmm.... some of this is still a bit beyond me but I get the concept and I've come along way since I started on this amp a few weeks back. I think in a way I kind of fluked getting my amp to where it is with quite a bit of experimentation and some good advice on this thread pointing me in the right direction.
Other than wanting a little more volume for louder playing clean (bigger amp needed for that obviously), it sounds great. I'm sure there is dozens of combinations of resistors and caps that could get rid of the muddy bottom end I was getting but it is pretty much gone now with the mods I made. Just one of my guitars had issues with the neck pickup and after lowering it on the bass side it is fine.
I plugged in my pedals to it last week for the first time and I was blown away - for one I could get a great volume boost but it sounded better than I could have imagined. My tube screamer and London fuzz worked unbelievably well through it and I couldn't have been happier. If I whacked a different badge on this and put it in a store there's no doubt it'd sell for a bucket load more.
Thanks again for helping me get there.
As for that new combo I'm just not sure what Crate are trying to do. Coming from a Marketing strategy background I can't quite figure it. It looks cheap and nasty and to me I think starts to position the brand in the budget end - whereas crate have historically made some good amps. If they wanted to make money and have a great reputation for a 5w amp - they'd just modify the circuitry a little, like we have, and perhaps throw in a better speaker. A few bucks extra but 10 times the amp that would sell like hot cakes and reinforce the brand as a quality one - whether budget priced or not.

Ryan

[jim p]

I have made a change to the reverb recovery amplifier circuit from what I originally used when adding reverb to the Crate V5 on these posts http://www.thefret.net/showthread.php?t=9379&page=11
For the recovery amplifier it looks like the best op amp to use at a reasonable cost is the NE5532. Also to reduce noise I am using both op amps in the dual package to make the recovery amplifier a differential amplifier to help lower noise pickup from the tank to the recovery amplifier. So another change that needs to be made will be to isolate the RCA jack on the output of the reverb tank as well as the input of the reverb tank. Also a ground wire will need to be added from the reverb tank to the chassis of the amplifier. Along with this if you are into making up your own cables would be to use a twisted pair inside of a shielded cable for the reverb tank output. The twisted pair should be connected to the inner and outer connectors of the RCA jack on the reverb tank while the outer shield would be connected to ground near the recovery amplifier the shield should be left floating on the reverb tank side.

So if you have not yet added reverb or have some noise pickup that you would like to try and eliminate you may want to go with this differential recovery amplifier.


If you have ever built a jfet buffer for your guitar output where you install a jfet right on the output jack of the guitar I just realized how to apply this to the reverb tank output. I have simulated a differential jfet buffer located in the tank that should balance and lower the output impedance of the reverb tank. With this as the input to a differential amplifier the noise from the tank should be close to none. I will test this out and if it works out will post the schematic.

[timmer114]

I think I burned something on mine. I had the v5 working just the way I wanted it, and when I went to change the c24 cap, the trace pulled up from too much heat soldering. I tried to make a jumper but I dont get any power light now,or preamp tube glow. Power tube works, amp turns on, just no power light or preamp tube, I wonder if frying the C24 trace caused this, though the jumper seems fine, or... if I bumped a nearby resistor or op amp with the soldering iron if that is what is causing the issue..

I can't seem to track down where I went wrong here. Let's say C24 socket is toast, the trace/pad came off the pcb...I should be able solder a hair up the trace itself and get a connection no?

Anyone have any ideas why I cant get power to the LED or to the preamp? The preamp is getting some voltage, it just won't come on. checked all fuses and connections, this all started when I pulled up C24, and the leg snagged on the pad and tore it up from the pcb. I wonder if there is a place I can jumper past the C24 pad..

Desperate here lol.

[jim p]

Look to see if one of the supplies that go to the op amp is shorted this would be the +14.7 and -14.7 volt supplies. Check for blown fuses on F1 and F2 this is the ac secondary that supplies the +/- low voltage supplies

I was just looking over your problem again I am guessing you tried to remove the capacitor with the PCB installed in the amplifier? The component leads are bent on the bottom of the board so you need to straighten them before you remove them. If you don’t there is plating in the hole that the component is soldered to that may be ripped out when you pull the component lead out. If you did that you may need to make repairs to both sides of the board.

[rock_mumbles]

Standard Tube Amp High Voltage Warning ... there is in excess of 300V inside the chassis!!!

I wouldn't use "only" solder to repair a pcb trace, I'd solder a wire to complete the circuit.

C24 is a signal cap, in the op-amp circuitry, without it "carrying signal" there will be no "amplification". Do you have +/-14V on diodes D9 and D10, according to the schematic this should be on the striped end of D9 and on the not-striped end of D10? The LED power comes off of the same power supply as D9 and D10. IF you don't have +/- 14V maybe check the two fuses on the low voltage power supply F1 and F2.

If you want to test the rest of the circuit, the preamp tube on, you could use a jumper wire from R10 (off of input jack) to R1 (input to preamp tube), note the amp will NOT have a volume control so it will be full volume

[timmer114]

Thanks for the replies guys, I really appreciate it.

Your right, I did pull up C24 from the top, big mistake. I checked the fuses, nothing blown there. I am thinking your right in that I will have to repair both top and bottom. Top seems simple enough to repair as I can visually see the traces. The bottom though.. im not so sure what I can do as the traces don't show through the bottom.

I'll have to pull the PCB tonight and see what I can figure out.

Okay so as Rock points out, the LED and C24 are on the same circuit I take it? I wish I had the board in front of me but I am on lunch break at work. I think there is hope here, I did get 300 volts off the preamp with the multi tester, so it is getting some power, guessing that the circuit is open though with C24 trace damaged. I'll drain the caps tonight and pull the board out. I think I need to figure out how to get C24 working again. I can still use the mounting holes and the top traces seem ok, it's the trace underneath that is giving the problem. So.. even if I do have the top traces soldered as I do right now, it's not going to work until I can figure out how to close the circuit underneath the board in C24.

Thanks again, your giving me some hope here =)

[rock_mumbles]

I don't have a V5 to look at (it's loaned out), but before you tear out C24 again, looking at the top traces you can see, where do they connect, one end of C24 connects to the op-amp pin 1, to one side of C26 and to one side of R12. The other side of C24 connects to R14. Then from what you can see on top check for continuity on each side of C24 to the "neighboring" component(s). Then you can find out where your trace problem is.

[timmer114]

Well, I did some continuity testing and found that two fuses did indeed blow, though they don't look it. I replaced them, and I do have power now to the LED and preamp, however I just get an annoying hiss. I am guessing this is where c24 comes into play.

I can see the top traces, but have no idea what was going on underneath the board, as you look at the board, underneath c24, it doesn't appear the bottom pads are hooked to anything.

But at least I have power again, just no sound. My tone cut control I made however, does adjust the tone of the hissing, just no input signal coming from my guitar.. I'll keep workin on it. Still looking to see if there is somewhere else I can jumper C24.

I wonder if the op amp blew, that would account for the lack of input signal and hissing I think.. hrmm I do have a burr brown op amp laying around somewhere, or I can just grab a new TL072 from radio shack. Thanks guys, still workin it out =)

[jim p]

A quick check would be to jumper pin 1 of the op amp to R14 either side will work but the C24 side of R14 will give you gain (can also jumper pin 1 of op amp to pin 6 as a test). If the connection from pin 1 of the op amp that is common to both C24 and C26 is still open you will have no signal to the rest of the amp. From looking at the picture of the board in post #168 the traces connected to C24 are all on the top side of the board. Also whatever op amp you use it should be a FET input op amp for high input impedance.
Also check pin 4 of op amp for -15 volts and pin 8 for +15 volts.

[timmer114]

Thanks Jim, I'll take a look at it tonight and try the jumpers. You have been a wealth of V5 info, and I really appreciate the help =)

[timmer114]

I managed to jumper off the existing traces to the cap in C24. I have sound now, but it's very distorted and loud. The volume control is very sensitive, and it sound as if there's a boss DS-1 cranked in front of the amp now. Hrmmm i'll keep at it, thinking the op amp is the culprit here though.

[jim p]

I have been bothered by the fact one of the last mods I do to an amp is to add reverb and when I do I get the 60 Hz noise back that I have been beating down. So looking into where this is coming from figure it is pickup on the reverb tank output. One of the bad things is that the output signal from the tank should connected to the recovery amplifier with a twisted pair inside of a shielded cable with the shield only tied to the recovery amplifier side. But even then the output of the reverb tank is a 1mV to 5mV signal at maximum and relatively high impedance. In all the tank installations I have isolated the input leaving the ground of the reverb tank through the reverb output shield. So a quick fix for that is to isolate the output RCA connector and run a ground wire to the chassis of the reverb tank. You still have a high impedance output from the tank so I thought of the FET buffer I have made for the guitar pickups but do to the reverb output coil floating you can even do better then that.

The buffer for the reverb tank produces a differential signal with a possible gain of up to 20 depending on the JFET used for the buffer. What this requires is to install three resistors and one to two capacitors in the reverb tank or right at the RCA jack. The remaining components are part of the recovery amplifier circuit. The circuit I built used a 2N6550 in the reverb tank but they are sold by only a few distributors and darn expensive. What you want is a JFET with low noise and high transconductance which is equal to low source impedance for the 2N6550 this is 25 to 40 mmho for 40 to 25 ohms source impedance. Instead of the 2N6550 in order of best to OK is 2SK170, BF862, BF861B and J309 the two BF fets only come in SOT23 package. What is unique about the circuit due to the fact you float the coil across the source to gate connection of the JFET you can get gain at both the source and drain side of the JFET. About the parts at the reverb tank the capacitor across the reverb output coil will cause frequency peaking so if you like twangy 2nF will do that I have no capacitor across the coil I did try from 100pF to 3nf something you can play with. R13 is to reduce the gain variation from JFET to JFET for maximum gain you can make it zero ohms. R1 is to set the current at between 1mA to 2mA if the current is high increase this if low lower it. R4 the 100k resistor could be increased to possibly increase the bandwidth of the reverb output or lowered to load down the tank for a darker sound say 50k to 25k ohms. So the source side of the JFET is connected to the outer connector of the RCA jack this is the low impedance side of the JFET while the drain is connected to the center conductor.

The recovery amplifier is a differential amplifier the gain of 10 from the JFET would be doubled if this amplifier was just unity gain but the amp has a gain of 10 so total gain is 200. So the circuit to the JFET is completed by the parts at the recovery amplifier R3, R2 R12 and R11. C1 and C2 along with R9 and R10 provide a high pass filter to help keep the low frequencies out of the recovery signal. C6 across the input will limit the high frequency input to prevent hearing your local AM radio station (because some of the JFETs are RF FETs). The first op amp U1 is to provide equal gain and high input impedance for the negative input to U2. The op amp can be an NE5532 dual op amp it has good low noise numbers and will work well for this application.

To sum it up I have a little hum but the power supplies in the Peavey Windsor I added this too are not great on the low ripple side I should add regulators.

Remember if you have both the input and output of the reverb tank isolate you will need to connect a ground wire to the reverb chassis. Also if you have a painted tank like a Ruby need to break the paint where the four springs that suspend the reverb assembly are attached to complete the grounding.

I want to correct one thing above the Jfet buffer is acting as a current source at both the source and drain so the impedance at the source and drain is the same 1 k ohms in the circuit as shown.

[timmer114]

I can't fix the thing, not sure what went wrong, but I went from having great headroom, to horrid gain at any volume position. Would burning up the op amp cause this? Something tripped the fuses in the amp, I replaced the fuses, and it powers on, but the sound is just beyond horrid with any tubes I use. It's pure distortion now. I can't seem to find which component failed that would cause me to lose all of my clean headroom. It's gotta be a cap after that op amp, maybe C25-or 26 or 21? I was able to jumper C24 to deal with the pulled up trace in that socket, but it doesn't matter at this point, it's all distortion.

Would a damaged op amp chip make the amp behave this way? I know I bumped an op amp leg with the soldering iron, but would that moment of heat burn up the op amp?

My gut tells me, that one of the components that shape the sound fried. The volume works, but the amp behaves like it's cranked wide open at the lowest volume, and only goes higher from there to a point of just chaos hehe.

Thanks for any tips, but I might need to try and locate a new circuit board. Loud doesn't have any in stock anymore =(

Hate to buy an amp just for the board, but I think I might end up having to do that.

[jim p]

You could consider just getting rid of the op amp look at post #160 and #168. An op amp can take quite a bit of heat so I doubt you hurt it that way. If you have not replaced the op amp that would be a start. Without a scope and signal generator there are only a few things you can check. You should check the DC levels of the output pins of the op amp at pin 1 and pin 7 they should be close to zero volts. Also check the voltages at pin 8 and pin 4 pin 8 should be approx 15 volts and pin 4 should be approx -15 volts. If you get bad voltages at pin 4 or 8 check to see if R19 or R20 have not been damaged or changed value due to high current when shorted. Also check the voltages at R19 and R20.

[SciHi]

... but I went from having great headroom, to horrid gain at any volume position.

So does the volume pot actually work? Crate pots have a high failure rate, my master volume on my v18 broke near the ground, so there was no signal sent to ground, just a variable resistor in line, it was loud, ugly, and noisy. Use your vom to test make sure the pot has continuity to ground and is working correctly.

[timmer114]

Hi,

The voume pot does work, it's just the signal that comes out the amp sounds cranked and loud at the lowest volume. As I turn it up, it gets louder and louder to a point where the amp just then buzzes oddly.

Thinking back, I blew 2 fuses on the board. What caused this, I am not sure. But since then, it sounds horrid after replacing the fuses. I am guessing some component failed, I just don't know which component failed.

Symptoms :
Went from pure lovely clean headroom all the way nearly to full on distortion at lowest volume that only get's louder as I increase the volume. Even at lowest volume, it sounds nearly cranked sound wise.

Lots of crackling going on when I touch the volume pot. Hmm. Perhaps that is the issue now that I think of it. Okay that makes sense to me, volume sounds cranked because well.. it is! but then would the volume pot still turn the amp up even more?

What pot would I need to replace it if I can't locate one from Crate. Let's say I had to buy one from Radio Shack, what am I lookin for, just a 250k linear pot?

Thanks,

[jim p]

Just to ask did you check the voltages on the op amp pins as I posted before the negative supply is on pin 4 and should be approx -15 volts. Then there is the positive supply on pin 8 which should be approx +15 volts. With no signal in to the amp the output pins of the op amp should be approx zero volts so pin 1 and 7 should be very close to zero volts. You should be able to check the pot with an ohmmeter to see if it is OK. It is an audio taper pot. There is an advantage to having a capacitor between the two stages of the op amp if there is some DC offset into the amplifier so when I posted to jumper pin 1 to R14 this was meant more as a test and not necessarily a final configuration.

[timmer114]

The Op amp seems to be fine, I replaced it even and same thing, mega distortion and a really sensitive flaky volume pot.

Starting to wonder if it's the volume pot...if I tap the volume pot lightly, the sound cuts in and out, it always stays massively distorted, but the sound cuts in and out just by touching either the volume or tone pots lightly.. hrmm.

[jim p]

Maybe the pot is bad or there is a bad solder joint going to one of the leads on the pot. I would look at the connections to the PC board and maybe just reflow them with a soldering iron and a little solder to make sure the joints are good. Also if you flexed the leads to much taking the board in and out one of the leads could have broken off from the pot. You could clean the pot it should not need it be being nearly new I use a little spritz of WD40 inside of the pot for that. Some people think WD40 is not a good thing to use so you can decide that for yourself. Also look to see if something near the pots might be shorting to the chassis.

[jfelser]

When I originally received the amp from AMS, I was thinking of sending it right back. But I bought it quite cheaply, so I figured at worse, I just got myself a reasonably priced 10" extension speaker cabinet. After googling mods for this amp, I stumbled onto this site. I immediately found a wealth of info provided within all the posts for the Crate V5. It helped me to make the decision of what direction to go. Thank you all!

Well, I just received back the PCB from my Crate V5 amp that I had Mark (deafelectromark) modify and I'm very impressed with his changes. These mods make this a very good small tube amp, with an excellent clean tone. I installed a Jensen P10Q speaker I bought cheaply on eBay a while back. Before reinstalling the head back into the cabinet, I tried several brands of EL84s and 12AX7s, a 5751 Sovtek and a couple of 12AU7s. I settled on a JJ EL84 and a Groove Tubes 12AU7, to keep the gain structure usable with my pedals. My Teles and Strats sound incredible, almost as good as through my Dr Z Maz 38 Sr, but at a fraction of the cost.

Now if I can only add some reverb . . . We'll be talking Jim :-)

[schenkadere]

I'd like to get mine modded. I was in contact with someone here, but soon after lost the email and I can't recall his username. He had a mod for about 40 bucks...send him the head and shipping. Can't believe I lost that!!! This post just reminded me.

[larryx]

Hello fellow fretters, well I wanted to thank one of our members named deaflectomarc. I just sold my v5 that was modded by him last winter. I got $350 for it! So thanks for not only making me money ,but taking a bad soundidng amp and making it really rock. All I had to do was throw a JJEL84 and a JJ12AX7 in it along with a speaker that I pulled out of my Marshall AVT20 and it sounds like a British Beast. Was the easiest sale I've ever made.


Thanks Mark!:applause

[schenkadere]

Hello fellow fretters, well I wanted to thank one of our members named deaflectomarc. I just sold my v5 that was modded by him last winter. I got $350 for it! So thanks for not only making me money ,but taking a bad soundidng amp and making it really rock. All I had to do was throw a JJEL84 and a JJ12AX7 in it along with a speaker that I pulled out of my Marshall AVT20 and it sounds like a British Beast. Was the easiest sale I've ever made.


Thanks Mark!:applause

Wow! I just put mine up on ebay...I won't get anything near that! :thwap

I did a quick demo that will either help or hinder the sale. :)

http://www.youtube.com/watch?v=8JQCkiDjRvw

[deafelectromark]

[QUOTE=schenkadere]Wow! I just put mine up on ebay...I won't get anything near that! :thwap

If you had sent it to me like you said that you were going to do, :crazyguy you wouldn't want to sell it, and when you were ready, you would get the extra money out of it. Loud industries took a good little platform and had 'too many cooks' work on it. Too bad they can't hear what they are doing- and I am the DEAF one!
I am still doing mods for $45.00 including return shipping for just the circuit board. If you want to send the whole chassis, it will cost you more in shipping both ways, but is less technical and more of a 'turn-key' operation. I add $5.00 to disassemble and reassemble the chassis from the circuit board and of course your shipping will be calculated to your home and shipping method. If you send me the weight of the chassis and zip code, I can get you a ballpark figure to help you decide if that is the best way for you to go.
Contact me via manoteal@cox.net
Mark

[SEDUK]

This is my first post to the forum, but I really want to recommend Deafelectormark and his mod. I had been playing my V5 through an old combo amp I have with an original Celestion G12-80 in it and it sounded barely tolerable with none of the feel of a real tube amp. After following this string for awhile, I decided I did not want to deal with doing a mod myself, but I really wanted to make the amp useful. So I contacted Deafelectromark and he walked me through the removal of the PCB (no desoldering needed on mine), which I sent out for mod. Meanwhile, I ordered and installed an Eminence Legend 1058 (highly recommended in The Tonequest Report and only $49.95 with shipping included). Mark turned it around within a week or so and I installed it with new JJ tubes ($12 apiece).

What a difference! It is not even the same amp. The bass is incredible, it is very touch sensitive and seems to sing with harmonic complexity. My Highway One Tele with a Glendale "twang" set of brass and aluminum compensated bridges sounds fantastic and depending on the volume, can do clean country all the way up to early Led Zeppelin. Surprisingly, I am not even missing reverb, as the complexity of the tone fills out the sound.

My reissue 1959 Les Paul Standard (Epiphone version, which is a very nice guitar for few $s; I compared it with many Gibson Les Pauls and it holds up well) with Burstbucker 2 in the neck and Burstbucker 3 in the bridge just screams. I can get a great Cream "woman tone" by cranking the volume on the V5 with the tone control at 5 (max treble) and the guitar tones rolled off, middle position with neck on 10 and bridge on 6. Fabulous overtones!

Last, but not least, my Jimmie Vaughan Strat loves this amp. If you set volume at 7, use the bridge or middle pickup and guitar volume between 5 and 7, it has a fantastic Texas blues sound. I can play it all night and never get tired of the interplay between the amp and guitar. Oh---and I can do this in the basement without complaint from the family, as the amp volume is reasonable. Having a total of $175 in the amp, it is a steal; and I didn't even have to heat a soldering iron. This a great way to go for someone who doesn't have time or inclination to get into the mods themselves. Thanks, Deafelectromark!:AOK

Update August 23, 2010: I now use a ElectorHarmonix Holy Grail reverb with the modified Crate and it is great!

[raja7052]

I sent my pcb board to mark to get the mod done, he turned it around in a week. what a difference, love the sound of it now. I highly recommend the mod to everyone and Mark is a real professional.

[Tarin]

Wow! i started this thread... my V5 is long gone and this thread's still busy.
Guess i'll have to start one on the Vox Tonelab ST pedal... one fine piece of equipment.

[deafelectromark]

Wow! i started this thread... my V5 is long gone and this thread's still busy.
Guess i'll have to start one on the Vox Tonelab ST pedal... one fine piece of equipment.

Tarin,
P.s Why didn't you let me have a go at yours when you still had it?? Good iron, good chassis, good cabinet, just needs a better speaker and some sand kicked out of it. There are thousands out there- anyone want to sell me theirs?? I will fix em up. :dude
Mark

[Tarin]

Deafelectro...
Know what, yesterday as i finished posting on this thread, i kinda wanted to get back at modding one of this since i never got the chance (sold mine at the first offer).
You're right, it does have a well built cab... saw one on the local CL for 80 bucks, mmmmmm what to do.

[jim p]

I posted this over at SEwatt and though I would post it here also for anyone thinking about adding reverb.

Well I am up to the point of ordering some boards made, just waiting on getting the Digital Sound Effector module form Belton somewhat. I have added enough holes to attach either the Sound Effector or the Digi reverb to the PCB. So figure I would go through a circuit description. The signal input to the board goes to W8 this connects to C5 in series with R4, R5 and R6 and the gate of Q1 a J211. The value of C5 a 1 nF and a total resistance of 1 Meg ohm will create a high pass filter to keep the bass out of the reverb (-3db approx 200 Hz). The connections W9, W10 and W11 are to replace R5 and R6 if a dwell (reverb input level) pot is desired. R4 can be used to set a limit on the maximum signal into the gate of Q1. Q1 the J211 jfet is used to make the signal input to the board a high impedance due to the fact the reverb module is a 10 k ohm input impedance device. W8 also connects to R3 that is connected to W6 and R2. W6 will be the connection to the control grid of the triode that was connected to the volume pot wiper. Moving back to Q1 (J211) its source is connected to R7 and C6 with C6 connected to R19 and C7. R19 and C7 is a low pass filter to limit the high frequency (approx -3db at 6.5 kHz) into the reverb module to prevent feedback the value of C7 can be increased if feedback occurs. The connection from R19 and C7 can be the input to the reverb module with R15 installed or the input to a common emitter amplifier with R10 installed. In the case of a VJ, Fender Champ, Crate V5 or any of the SE amps having the volume control followed by a triode connected to the output tube gain will be required before the input to the reverb module so R10 would be installed and R15 omitted.
The reason for adding gain to increase the signal into the reverb module is two fold, one the greater the input signal the better the signal to noise ratio this is the same for a digital reverb or a spring reverb. Second being a digital device if the signal is low less of the dynamic range of the system will be used and with low levels digital distortion may become noticeable. The gain required for a stock VJ is this, an EL84 will have an input voltage of approx 5 volts RMS at full power this is from the triode connected to its control grid with an approx gain of 50 so the signal at the control grid of the triode is 5 divided by 50 for 100millivolts RMS. Now with this board installed the signal to the control grid will be attached to a resistor divider R3 and R2 so twice the signal will be present at the volume pot wiper for 200 millivolts into the reverb module. The spec on the reverb module is 1.5 volts peak which is approx 1 volt RMS so 1 divided by 0.2 (200 millivolts) is 5 so a gain of 5 is required. Which leads to the common emitter transistor amplifier Q2 R8 and R12 are a voltage divider to bias the base approx 50 volts with a plate supply of 250 volts at W12 the input impedance to the base of the transistor is R8 in parallel with R12 in parallel with R13 times the transistor beta of approx 80 for approx 30k ohms. With R18 installed so the output of Q2 is connected to the input of the reverb module the AC impedance at the collector of Q2 is R9 50k in parallel with 10k for 8.3k ohms. The AC gain is 8.3k ohms divided by R13 so with 1.5k ohms for R13 it is 5.5. There is some signal loss at Q1 due to its source impedance of approx 160 ohms and R19 in series with the input impedance of 30k so overall the gain should be approx 5 from W8 to M4 (reverb module input). The output of the reverb module M2 through R16 is connected to W3 this point is to be connected to the reverb level pot. With the circuit as described the output of the reverb will be 5 times greater then the dry signal so you may want to half the input at Q1 by making R6 a 470k R5 a 470k and R4 1 ohms so it will just be 2.5 times greater. The reverb level pot connections are as above the top of the pot connected to W3 the wiper connected to W4 and the bottom connected to W5 (ground). To allow the use of a footswitch Q3 and R11 are on the board so when W13 is pulled to ground the mosfet is off and the wiper of the level pot is not shorted to ground with the switch open Q3 is turned on and the wiper is shorted to ground. When the reverb level is all the way up the mosfet will short the output of the reverb module to ground therefore you may want to use a 10k resistor for the value of R16.

If you were to add this module to an amplifier with master volume or a push pull amplifier where the signal level at the volume control is greater then 1 volt RMS R4, R5 and R6 would be used as a divider to limit the signal to 1 volt RMS. Then R15 would be installed so the signal directly from Q1 would be applied to the reverb module input. Then C11 a 100nf 100 volt cap would be installed and I would use a 20 to 25k ohm pot for the reverb level that will be connected to R17 with R18 omitted as well as R16 omitted. You will need to calculate the gain required for signal matching with 250 to 300 volts at W12 a gain of approx 22 is possible with an output of up to 180 volts peak to peak.
So unlike standard reverb tank connections with tube or solid state recovery circuits this circuit allows you to locate the reverb at a location in the amplifier with high peak to peak signal levels.

The power supply connections to the PCB are W1 and W2 with a 6.3 volt AC heater supply the two secondary connections go to W1 and W2. On an amplifier with AC heater supply D1-D4 are installed if a center tap is connected to ground it will need to be removed also if there are pseudo center tap connections through resistors in the amplifier they will need to be removed. W14 the AC ground should be connected where the center tap used to be connected. On an amplifier with DC heater supply D2 and D3 should be omitted to prevent ground loops due to diodes in parallel and W14 connected to the ground of the filter capacitor for the DC heater supply. If the amplifier has +15 volts you can connect the positive to W1 and ground to W2 then omit D2 and D4 replace D3 with a short and D1 with a 50 ohm 1 watt resistor.
With an AC supply D5, C3, D6, C4 create a positive voltage doubler. This is followed by R1 a series dropping resistor and D7 a 12 volt zener diode with filter cap C10. This provides Q1 the J211 with a drain supply of 12 volts because 5 volts would be insufficient to insure linear operation with device to device variation of jfets.

Regarding cost the parts are approx 8 bucks without pots the PCB 20 bucks each in quantity of three and the best price for the module is 15 bucks.

The schematic is here http://i1020.photobucket.com/albums/af330/vactube/Digireverbschematic31210.jpg

The layout is here
http://i1020.photobucket.com/albums/af330/vactube/Digireverbpcb31210.jpg

Let me know if you find any errors, thanks.

[jim p]

I have three blank PC boards on order by what things are costing out to be if I had 10 or more people who wanted these the cost would be around 40 to 50 bucks. That would be all the parts on the PCB required and the reverb module you would need to do the assembly. It might be possible to include the level pot at this price also. (the knob?)

[deafelectromark]

I have three blank PC boards on order by what things are costing out to be if I had 10 or more people who wanted these the cost would be around 40 to 50 bucks. That would be all the parts on the PCB required and the reverb module you would need to do the assembly. It might be possible to include the level pot at this price also. (the knob?)

Reverb is better outboard as well as the effects. Amps are what they should be be. Amps- and nothing more- nothing less. KISS
M:dude

[jim p]

Well I thought I would post what I have for right now. I have the PCB and have installed most of the parts for operation. I tested the FET buffer stage and common emitter stage using two 9 volt batteries for a power supply. The FET is OK with an input signal up to 1.5 volts RMS so no problem being the largest signal in should be limited to 1 volt RMS. Also with the VJ it will only be 200 millivolts at full volume out. Loading the common emitter stage with a 10k resistor I got a gain of 4.8 so that is OK also. The one down side of the cheapest PCB from ExpressPCB is all the unmasked copper makes it easy to have a solder bridge on the board (I had two from assembly). If I do the boards in a quantity I will see about solder mask and silkscreen to make life easier. I don’t yet have the Digi-reverb module but I do have the Sound-effector which is the same size so I used that to check dimensions and to take pictures for now. With the module mounted on the back using nuts for a gap the PCB and module are 1.5 inches high by 3.8 inches by 2.5 inches. If you mount the module off the edge of the PCB on the top the height is 1 inch with a width of 3.8 inches by 3.8 inches.

http://i1020.photobucket.com/albums/af330/vactube/frontmountedmodulepic.jpg

http://i1020.photobucket.com/albums/af330/vactube/sideviewbackmountedmodulepic.jpg

http://i1020.photobucket.com/albums/af330/vactube/topviewreverbPCBpic.jpg

[jim p]

Well I built up a board and first installed it in a Ver 1 VJ combo amp with AC filaments. Couple of problems with that being the first stage triode plate trace runs parallel with the control grid for the second stage so with 330k in series to the grid and 330k to ground you have signal with the volume pot turned all the way down due to coupling. The second problem was AC pickup that did not exist with the stock setup so instead of adding a DC heater supply and cutting up the pcb I put it back together to try a different amp.
Next I put it in a Crate V5 that has been modified by removing the op amp that was on the input and has the volume control between the triode stages. The AC heater supply for the power tube is tied to ground on one side in the amp so on the reverb board only one diode D4 is installed and a short is installed at D2. Then W1 is wired to ground and W2 is the AC input to the supply. I used coaxial cable to connect to the wiper of the volume pot to the input to the reverb board with the coaxial cable grounded only on the volume pot side also used coaxial cable on the output of the reverb board with the ground near the control grid. This uses the voltage divider of R2 and R3 on the reverb pcb to mix the signals. With this I was getting some AC pickup (ground loop or pickup of AC to DC supply on pcb) so I put the resistors for the signal mix down on the amplifier pcb with 330k from the volume pot wiper to the control grid and 330k from the control grid to the wiper of the reverb level pot. With this I get just a little pickup when the reverb level is at maximum which is surf guitar level. Adding a ground from the signal side of the reverb board to a ground near the triode control grid took a little more of the noise out.

I need to see what the signal levels are like on the pcb I split the input to the board with two 470k resistors for half the signal into the board. But found I lost a lot of gain at the common cathode amplifier output so the module input is less then 10k as the data sheet states.
I will have to look into getting some sound clips posted.

The reverb sounds fine at least equal to the digital reverb in the Bugera V5 I have. On the Bugera I did change the stock input to the reverb to a connection at the volume pot. I also changed values in the common cathode amplifier on its output due to clipping on the stock circuit.

I plan on adding this reverb to a 6AQ5 push pull amplifier that I just got a Hammond chassis for.

[jim p]

Looking at the input and output of the Digi-reverb I am getting numbers that are different then the data sheet. Part of the problem could be the approx 30 years old Phillips scope I am using, but instead of 1.5 volts peak it looks like the most you want at the input is 1.5 volts peak to peak. One thing I am sure of is the input impedance is closer to 4k then 10k ohms as the data sheet states. The reverb looks to peak with more gain at approx 2 kHz then level off. There is also some nasty looking high frequency odd harmonics in its output if you do overdrive it. So it looks like I may have just needed a jfet buffer on the input due to the low input impedance and you don’t need the common emitter gain stage so much. I might increase the frequency roll off into the reverb module by increasing the capacitance in the low pass filter I have after the jfet buffer. Wishing I had a digital scope to freeze the signal coming out of the module to get a better idea of what is going on. Also be nice to have one that has been calibrated in the past decade.

[jim p]

I have posted two sound clips of the Belton Digi-reverb mounted on the PCB I designed installed in a Crate V5 amplifier. It is my son playing with the amplifier connected to a cabinet with two Jensen Special Design 10 inch speakers. The reverb is set at the mid level in one clip and at maximum in the other.

[mars2010]

I have posted two sound clips of the Belton Digi-reverb mounted on the PCB I designed installed in a Crate V5 amplifier. It is my son playing with the amplifier connected to a cabinet with two Jensen Special Design 10 inch speakers. The reverb is set at the mid level in on clip and at maximum in the other.

after reading through all these pages of mods

these sound clips are great, very nice playing and tone...
:applause

it's incredible how much time and dedication jim p put into working on this amp
very interesting stuff...

[DeanEVO_Dude]

I just picked up my Crate V5 amp, changed the speaker (Eminence Patriot Ragin Cajun) and I kinda like the way it sounds... They should have added $50 to the price and equiped it with this speaker to begin with.

Anyway, my soldering iron will be aquainted with this amp either next weekend or the one after. The first thing that will change is the gain on the op amp, move it more 1.5:1 or so on the first stage and around 2:1 on second stage. Then to tackle the the tone control... But one mod at a time...

[DeanEVO_Dude]

Jim P,
I have a question for you, I want to add a volume control to my V5 and what I was going to do was replace R27 with a 10K audio taper pot, and Radio Shack has said 10k audio taper pot. R27 is a 1/2 watt resistor, and the 10K pot is also 1/2 watt... one leg of the pot tied to R16, the other leg tied to gnd. and the wiper tied to what used to be the junction of R16, R27 and pin 2 of the 12AX7/R7. Would this work OK? Are there better values for the pot and R16 that I could use for better control?

Thanks.

[deafelectromark]

Jim P,
I have a question for you, I want to add a volume control to my V5 and what I was going to do was replace R27 with a 10K audio taper pot, and Radio Shack has said 10k audio taper pot. R27 is a 1/2 watt resistor, and the 10K pot is also 1/2 watt... one leg of the pot tied to R16, the other leg tied to gnd. and the wiper tied to what used to be the junction of R16, R27 and pin 2 of the 12AX7/R7. Would this work OK? Are there better values for the pot and R16 that I could use for better control?

Thanks.
Hi,
The best place for a volume control is between the two tube sections. The wattage is irrelevant as minimal power is dissipated at these low currents. A 10K control is probably too low for a high impedance circuit, I would use at least a 250K control to not load down the preceding stage. Look back at the earlier posts and schematics and see that what you need to do is reduce the voltage going into the grid of the second half of the 12AX7 from the plate of the first half. The only 'trick' is to have it low enough to keep noise and stability under control (<1 meg or so). But if it is too low (<50K), you lose gain (and tone).
Hope this helps.
Mark

[deafelectromark]

Jim P,
I have a question for you, I want to add a volume control to my V5 and what I was going to do was replace R27 with a 10K audio taper pot, and Radio Shack has said 10k audio taper pot. R27 is a 1/2 watt resistor, and the 10K pot is also 1/2 watt... one leg of the pot tied to R16, the other leg tied to gnd. and the wiper tied to what used to be the junction of R16, R27 and pin 2 of the 12AX7/R7. Would this work OK? Are there better values for the pot and R16 that I could use for better control?

Thanks.

See post #16 for my mod for a starting point. Jim P takes it to the moon and back in 20 pages if you really want to get into it, but you can make this a great amp with NO added parts and very little work.
Mark

[DeanEVO_Dude]

Hi,
The best place for a volume control is between the two tube sections. The wattage is irrelevant as minimal power is dissipated at these low currents. A 10K control is probably too low for a high impedance circuit, I would use at least a 250K control to not load down the preceding stage. Look back at the earlier posts and schematics and see that what you need to do is reduce the voltage going into the grid of the second half of the 12AX7 from the plate of the first half. The only 'trick' is to have it low enough to keep noise and stability under control (<1 meg or so). But if it is too low (<50K), you lose gain (and tone).
Hope this helps.
Mark

Thats where R27 is, between the two sections of the 12AX7 and after the tone control (just like the Palo. 508). The only reason I chose the 10K pot value is because R27 is a 10K value. I just noticed that the Palomino uses a 10K linear taper...
If I use, say, 100K pot, should I change the value of R15? I know that the circuit is a voltage divider, but I ain't so good with theory, so...
My intent is to keep the "gain" control on the 2nd stage of the op amp and add a volume control to the circuit (put it where the power led is and move the led above the switch). So far, with the speaker change (Ragin Cajun) I like the sound of the amp, but it is just too loud (almost never move the "volume" past 9 o'clock). I want to be able to put the "gain" up to 1 or 2 o'clock and still be able to be tolerated by the others in the house... LOL
I am also going to go back and re-read alot of this thread...

Thanks. :AOK

[jim p]

It sounds like you are going to keep the exiting volume control as a gain control and then add a volume control after the first triode stage? As stated above in another post I would go with a 100k audio to a 250k audio pot for the volume control. Remove R15 and R27 connect one side of the pot to ground the wiper to what was the junction of R27 and R15 and the top of the pot to where R15 connected to R29. The reason the 508 has 10k there was to maintain levels for the line out that amplifier had.

If you want you can remove R7 also. If you need more bass change C24 to 50nf to 100nf but for overdrive you don't want a lot of bass going into the overdriven tube so stock value may be good for what you are doing.
You could also go all tube by moving the gain control to where R15 and R27 is and adding a master volume at R16 look around it has been covered in previous posts.

[DeanEVO_Dude]

It sounds like you are going to keep the exiting volume control as a gain control and then add a volume control after the first triode stage? As stated above in another post I would go with a 100k audio to a 250k audio pot for the volume control. Remove R15 and R27 connect one side of the pot to ground the wiper to what was the junction of R27 and R15 and the top of the pot to where R15 connected to R29. The reason the 508 has 10k there was to maintain levels for the line out that amplifier had.

If you want you can remove R7 also. You may want to change the value of C1 to 220nf the overdriven tube will sound better with less bass and reducing C1 will do that.

Yes, that is exactly my intent... To clarify, I want to put the wiper (onward towards R7 and pin 2 to gnd at minimum volume, right? So, counter-clockwise ties wiper to ground and clockwise (max volume) ties the input of R15 straight on to the tube (pin 2). Thanks.
What is the impact of removing R7? Will it change the tone (frequency respons)? or just the voltage going into the 2nd stage of the 12AX7 (level/volume)?

[jim p]

Yes how you are going to connect the pot is correct removing R7 will give you a bit more signal to the control grid it would matter more if you had a master volume at the R16 location for this mod not much difference.

[DeanEVO_Dude]

Yes how you are going to connect the pot is correct removing R7 will give you a bit more signal to the control grid it would matter more if you had a master volume at the R16 location for this mod not much difference.

Excellent! I have a 500K auido taper for "just such an occasion." :dude

To all who have posted replies, thank you very much! :AOK

[jim p]

Warm or cold bias? Being you are going to over drive the tube you may want to change how the first triode stage is biased. If you look through the posts you should find a link to a web page that goes through tube bias and tone. In short using a high value cathode resistor from approx 5k to 7.5k is cold biased with the tube near cutoff leading to a crunchy rock tone. Warm biased is when you use a low value approx 750 ohms so the tube is near saturation for more of a blues tone. If you have enough tube stages being overdriven sometimes the setup is 1st stage warm 2nd stage cold or the reverse. Using the op amp you will only have one tube overdriven with the volume control between the tubes.

PS: Was thinking about the warm and cold bias points a bit more and on the down side if you do this to the first tube in the amplifier it may limit your clean headroom. With the op amp because you can get less than unity (1) gain it may not be a problem. But if a tube by itself was the first stage the signal from the guitar could be great enough to cause saturation or cutoff. So with tube only it may pay to play with the bias point if you have a master volume pot connected to the EL84 and just on the second triode.

[DeanEVO_Dude]

Sorry for all the questions, as I said before, "I ain't no engineer"... lol

Any way, here is my current plan for the next step of mods on this amp (added the 500k volume in place of R15 and R27). The amp is still too loud, so I want to make the following changes:
R10 - 68K (still debating this)
R13 - 150K
R14 - 68K
and add 27K in series with CW-1

The rest of the circuit around the op amp remains unchanged. What are the effects of these changes on the frequency of these circuits specifically, will/should I need to adjust the values of any of the 4 caps (C21, C24, C26, and C27) to keep the frequency response (for the most part) unchanged (I don't mind if it gets a little darker, just not brighter).

By the way, jim, I am thinking about your suggestion on changing C1... Undeceided as yet. Thinking about a switch to swap 2 or 3 different cap values there. Still may remove the op amp altogether in favor of your "straight to the 1st triode" with the high freq. emphasis circuit.

[jim p]

I have to take some more time to see what effect some of the value changes you are posting would have on the frequency response of the op amp circuit. Changing R10 will have no real effect on this amplifier if it was a tube amp with it connected to the control grid it would lower the high frequency response. You say the amp is still too loud? So that makes me think you want an overdriven amplifier sound at low volumes, if that is the case you may need to consider adding an attenuator such as an l-pad which you can find in previous posts. The other way to go is to add a variable voltage regulator circuit to reduce the plate supply of the EL84 that is also covered in earlier posts.
Going back to the op amp circuit increasing the value of R13 is not a bad idea you could even remove it. One thing you do not want to do is to have high gain in the op amp circuit so you have clipping in the op amp so removing or increasing R13 will lower the overall gain in the op amp stages. You can also lower the value of R19 and R20 to increase the supply rails of the op amp for more headroom in the op amp stages say to 50 or 75 ohms instead of the stock value of 150 ohms.

[jim p]

If you are thinking about adding a standby switch this Carling switch model 2GG51-73 that they have at Antique Electronic Supply (P-H520) fits right in place of the stock switch http://www.tubesandmore.com/?OVRAW=marshall+amp+parts&amp;OVKEY=amp+marshall+part&amp; OVMTC=standard I don’t want to get into the debate of need for having a standby switch. In the past I did not think they were necessary over time through some of the things I have read about tubes I think it can’t hurt the choice is yours.

[DeanEVO_Dude]

I have to take some more time to see what effect some of the value changes you are posting would have on the frequency response of the op amp circuit. Changing R10 will have no real effect on this amplifier if it was a tube amp with it connected to the control grid it would lower the high frequency response. You say the amp is still too loud? So that makes me think you want an overdriven amplifier sound at low volumes, if that is the case you may need to consider adding an attenuator such as an l-pad which you can find in previous posts. The other way to go is to add a variable voltage regulator circuit to reduce the plate supply of the EL84 that is also covered in earlier posts.
Going back to the op amp circuit increasing the value of R13 is not a bad idea you could even remove it. One thing you do not want to do is to have high gain in the op amp circuit so you have clipping in the op amp so removing or increasing R13 will lower the overall gain in the op amp stages. You can also lower the value of R19 and R20 to increase the supply rails of the op amp for more headroom in the op amp stages say to 50 or 75 ohms instead of the stock value of 150 ohms.

Yeah, too loud for me... Just slight turns of the dials, if 7 o'clock is at min, going past 8 o'clock is loud. I need "baby is sleeping, shhhhh" kind of volume with the dials that low (yeah, no amp overdriven, that what pedals are for). I am just trying to get a minimium amount of gain out of the op amp. I have been using an online "op amp gain calculator" to determine my resistor values. Basically, what these values give me is at 12 o'clock on the "gain" knob a gain value of 1.2 or so, max on the dial gives about a 4.8 (that is total from input on 1st stage to output on 2nd). I like distortion and boost from those little boxes you put between your guitar and amp. And, yes, I am try not to overdrive the op amp at all costs. So, with a gain of 1.2 on stage 1 and variable gain of .5 to 4.0 on the second, I should reach that goal. At any rate, one mod at a time... maybe the tone stack next... :deadhorse:
Anyway, thank you very much for your vast knowledge and your willingness to share it with us hackers. :thankyou

P.S. If it is of any help, my first tube amp was a Fender Champ 600 RI... talk about not loud at all, even when cranked from what I remember. Nice amp, should have never sold it.

[jim p]

Thinking about your problem with the volume level makes me wonder if it is just the sensitivity of the controls that is the bother. On the volume control you just added maybe a lower value pot would have been the better choice. You could also put a resistor in parallel across the pot to reduce its sensitivity say 100k you could use the one you removed at R15 if it is still in one piece.

[mars2010]

hello, i've read through all these mod posts and i've done some minor changes to my v5. i changed the stock speaker for a jensen mod 10-50, i changed the sovtek 12ax7 for a groove tubes 5751, i changed the sovtek el84 for a mullard el84. i get a nice clean sound up to about 6 on volume, then a fuller overdrive sound past that. i keep the tone between 6-8, the bass is tight, the highs and mids are well balanced. i tried the amp out live with drums and piano in a small church, i actually had to turn down to about 4-5 on volume to blend in nicely. overall, i love this little amp and after a lot of research i think these simple mods made it much better...

[DeanEVO_Dude]

Thinking about your problem with the volume level makes me wonder if it is just the sensitivity of the controls that is the bother. On the volume control you just added maybe a lower value pot would have been the better choice. You could also put a resistor in parallel across the pot to reduce its sensitivity say 100k you could use the one you removed at R15 if it is still in one piece.

After a little more playing on the amp, I think you are right on your diagnosis, Dr. :dude I think that I will get a 250K pot and try that instead of the 500k I have in there now. So far, I am liking what the amp is sounding like, though I am leaning towards your mod for removing the op amp from the circuit, though I have not done my gain-reducing mods yet (this weekend's project).

For those of you parusing this thread who have one of these amps, the speaker that I chose was an Eminence Ragin Cajun (CL purchase 6 month ago, $40). I have a Eminence Redcoat Ramrod in my H & K Edition Blue which I like alot. Some day, I might try that in this little V5.

[deafelectromark]

hello, i've read through all these mod posts and i've done some minor changes to my v5. i changed the stock speaker for a jensen mod 10-50, i changed the sovtek 12ax7 for a groove tubes 5751, i changed the sovtek el84 for a mullard el84. i get a nice clean sound up to about 6 on volume, then a fuller overdrive sound past that. i keep the tone between 6-8, the bass is tight, the highs and mids are well balanced. i tried the amp out live with drums and piano in a small church, i actually had to turn down to about 4-5 on volume to blend in nicely. overall, i love this little amp and after a lot of research i think these simple mods made it much better...

You're on the right track.:applause
Mark

[bfglp]

hey new guy here. my v5 arived today nice cheep auction buy. swaped the junk plastic speaker for a clestion g10d 30 i had laying around, made a huge diffrence.

is there a mod for just bypassing the opamp?

[jim p]

There are a couple of mods posted for how to bypass the op amp #168 here http://www.thefret.net/showthread.php?t=9379&page=9 is one that I posted and there are a few more.

[bfglp]

thanks thats exactly what i wanted.

[jim p]

I am in the process of getting together some reverb kits for three people at this point. The cost is approx 55 bucks for the DIY you assemble the PCB kit using the Belton Digi-Reverb module. I have posted information about it here http://www.thefret.net/showthread.php?t=9379&page=21
If you are interested you can get a hold of me over at SEwatt http://www.sewatt.com/forum by posting a message to Fondue, thanks.

[jim p]

The following are instructions and schematics are for a cheep way to add the Belton Digital reverb to the Valve Jr amp, but the Crate is similar so you can basically do the same thing. If you use the +15 volt supply for the +5 volts install a resistor of 62 to 82 ohms 1 watt to 2 watts in series with the regulator. Best to go with the TO 220 regulator and a 62 ohm 1 watt resistor in series.
Cheep reverb mod with Belton module on stock VJ or similar amplifier. The input signal to the reverb module is going to be a voltage divider connected to the plate of the first triode after the coupling cap. You can go with a direct connection of a 220k resistor in series to the input of the reverb module or use a 2.2nf to a 4.7nf capacitor in series. Having the capacitor will reduce the bass into the module and increase the gain at low frequencies of the first triode. Taking the input of the reverb here will reduce the gain of the first triode by approx 20%. Also if there is a tone stack or tone shaping network before the volume control the reverb input and output will bypass it. For the output of the reverb a 10kA to 25kA pot connected to the reverb out will act as a level control. The wiper of the reverb level pot should be attached to the control grid of the second triode through a 220k resistor. Another 220k resistor should be installed between the control grid of the triode and the wiper of the volume pot. These resistors will raise the impedance of the control grid making it more sensitive to noise pick up. So they should be installed at the socket pin of the tube.
The power for the reverb module will come from the heater supply. Using two Schottky diodes with the anode of one connected to one of the heater secondarys and the anode of the other connected to the other anode secondary with the cathode tied together. Connected to the cathode should be a 2200uf 16volt cap this will provide approx 7.6 VDC for the input to a three terminal 5 volt regulator. You should use a LDO (low dropout voltage) regulator for this Mouser has this in a TO 220 package LD1117V50 you should be able to use a TO 92 package as well such as this one LM2931AZ50R with a power dissipation of approx 300mW max. At the output of the regulator I would install another 2200uf 16 volt cap. This power supply implementation requires the amp to have a DC heater supply if not you will need to add a full wave bridge rectifier for the raw supply into the +5 volt regulator. You can find the data sheet for the Belton module here http://www.belton.co.kr/index.php?mm_code=75&recomm=B&class_code=CLS0002105 they have the module for 15 bucks at Antique Electronic supply I would go with the medium delay.
I do not think this is the best way to install the module into the amp but it is the cheapest way to go.
Pin connections to module
Pin 3 to volume control ground.
Pin 4 to 220k resistor connected to coupling cap of first triode stage.
Pin 2 to top of reverb level pot
Pin 5 to ground side of heater filter cap
Pin 7 to output of +5 volt regulator

[bfglp]

finnished the no opamp mod and im very pleased with my v5 now. this mod and a celestion speaker give me nice bell like tones with my strat with moderate tube brakeup when cranked. thanks!

just wanted to add that it now sounds more like my ol champ. i also pluged it into my 210 closed back cab with g10 35's and broke out my les paul :happy sent me to tone heven.

[Monodexterous]

Short story told long... My son is an aspiring blues harp player living in NYC. We chatted often about the virtues of tube amps in creating that wonderful overdriven sound from the early blues recordings. He bought a Crate V 5 from GC in NYC maybe 2 years ago. It had some difficulty right off the bat. The magnet fell off the speaker!? you can imagine the effect that had on the sound, which was already cheesy because of the flimsy stock speaker.
Anyway, he brought the amp home to Philly, and left it with me while he was touring in a traveling theater production. I replaced the stock speaker with a Jensen C10R. I was concerned about getting a speaker with a larger magnet because of potential size issues. No problem it fit right in an the improvement in sound was apparent and impressive, altho a little harsh an no bottom end. Googling Crate V5 mods, i came upon this site and thread. It was my good fortune to read Deafelectromarks assessment of the design and his comments about the simple mods he did which apparently had a great effect on the sound of this little amp. I corresponded with Mark, and being cautious about doing such a mod myself and fearing electric shock or worse, I sent the whole chassis to Mark. Mark and I dialoged many times about the progress, during which I asked him many inane questions about guitars, amps etc. My naievete was obvious but he answered my questions in thoughtful and informative manner. When I got the amp back, and turned it on, I was a little disturbed; weak sound and not real loud. Shortly thereafter a loud squeal really freaked me out. Bad power tube? I tapped the stock Sovtec EL84 and yes, it did crackle and pop. Out it came and in went a vintage GE EL84 Mark had sent along with the amp. Ahhhh! Much better, tho not a huige amount of overdrive. Corresponding with Mark about my concerns, we deceided to go with a new JJ EL84. I bought two matched from Tubedepot for 17.95 on sale. When they arrived i tore open the box, plugged one in with a new Tungsol 12AX7 and WOW!. Sweet sparkly clean tones and a throaty OD tone I was hoping for. My son came home for TG and we jammed a bit. He was totally enamored with the sound of this amp now. His harp mike will OD the amp when on about 5. With a vocal mike, it creates a Little Walter sound, and a roomy almost reverb effect. My Strat with the amp on 6-7 reminds me of Live at Leeds or some of the brighter ACDC tones. So, thanks Mark for deconstructing this little gem and bringing it back to life.
PS: My son is giving me back my BJ and taking the CrateV5, believe it or not, the Crate sounds better!

[SciHi]

hey new guy here. my v5 arived today nice cheep auction buy. swaped the junk plastic speaker for a clestion g10d 30 i had laying around, made a huge diffrence.

is there a mod for just bypassing the opamp?

So finally just sold the v5. Fun experience, it was sounding real good, took it to Marshall territory, with a similar Celestion G10-30 speaker, dual inputs, opamp removed, normal channel marshall tone control, and master volume, $160. I feel fair price to both parties...

[lute760]

Step by step modifications done to Crate V5 amp

1) Remove the amplifier from cabinet. First remove speaker jack then the six screws holding back cover of amplifier then with amplifier upside down remove four screws two on each side of cabinet that hold amplifier chassis in cabinet. (Note: you may want to enlarge the holes slightly in sides of cabinet and on back cover to make reinstallation and future removal easier)

2) If you haven’t already done so (you do have this unplugged right?) get out a dc voltmeter the highest voltage in the amplifier is approx. 320 volts DC measure from chassis to R25 should be 0 to 15 volts if so you are safe. This amplifier has a bleeder resistor R25 so supplies should drop after power down.


3) Remove preamp (12AX7) and power tube (EL84 6BQ5) put them some where you wont break them.

4) Next remove knobs on front panel may require flat blade screwdriver and a thin piece of wood to work against to prevent scratching front panel. The pots are D shaft type walk then off gently. Then remove nuts holding pots and ¼ inch jack on front panel.


5) Now make note of all the connections to the PC board because you are going to remove them. If you have a digital camera now is a good time to use it. Also if you print out the schematic note wire color and location on it. The faston connectors J4 J5 J1 and J2 may be hard to remove don’t break them of pcb by working them back and fourth.

6) Next remove the six screws that hold PCB into chassis and take it out. (hope you are putting parts someplace you wont loose them)

PC Board modifications
(See attached pictures of mods and changes to schematic also pic DSCF0947.jpg in previous post is the pre emphasis mod the tone mod is incorrect in that post tie unused side of pot in tone control to wiper not ground or unconnected up to you)

1) You are going to be removing approx 10 parts. You will need solder, solder wick, soldering iron, needle nose pliers and desoldering tool. In manufacture the compnet leads have been bent so desolder a componet lead then straighten it before removing or you may damage PCB plated feedthrough.

2) This modification will use the two Op Amp stages for an input buffer and small gain to over come loss due to pre emphasis circuit that will be added. Desolder and remove volume pot from PCB. Next remove R13 this makes IC1-A a unity gain buffer. Remove C26, C24 and C27 replace C24 with a 47nF 50-100 volt poly cap.C24 sets the low frequency limit at input to the amplifier with 47nF this is approx 125 HZ 3db down (for more bass use 100nF). In the place of C27 install a 33k ¼ watt resistor this equals a gain of 1.22 for IC1-B (want to keep gain low so first stage tube will clip before the Op Amp with overdrive).
ERROR Value of C24 should be 100nF lowest frequency from guitar is 82Hz.


3) Pre emphasis circuit For the tone control to be able to cut, boost and be set for flat response the high frequencies need to be boosted first. So C25 needs to be removed if you want replaced or use it again for this mod. Install one lead of a 100nF 50-100 volt cap into plated hole (via) that is connected to pin 7 of IC1 in the second hole of C25 insert lead of 33k ohm ¼ watt resistor with a 10nf capacitor accost it then connect the other lead of the 33k resistor to the second lead of the 100nF capacitor. If you want full treble brighter you can lower value of R2

4) Tone stack and volume control Here we will put volume control after tone stack and first tube stage so you will be able to overdrive input tube and still control volume. Remove C5 C6 C28 and C4 Change C6 to a 22nF 50-100volt poly capacitor. (Here a lower value cap will raise where the tone control will cut the highs higher value will lower it.) Now the volume control remove R15 and R27 using the volume pot removed from the board you will need to bend the leads 90 degrees towards the back of the pot to attach 1 ½ inch wires to the three terminals of the pot. Also need to insulate PCB were pot was attached to prevent shorting (three layers of electrical tape works) looking at the front of the pot as use to be connected to the PCB the right side terminal connects to the plated hole C28 that connects to R29 the center terminal (wiper) connects to the plated hole of R27 that connects to R7 and control grid (pin 2) of the 12AX7. The last terminal goes to the plated hole of R27 that goes to ground. (note be careful the leads soldered to pot do not short to metal back shell of pot no sound out of amp)

5) Oscillating power tube in testing the amplifier found output did not clip symmetrically and oscillated when clipped. Based on the tube data sheets the cathode biasing is to high in value. Change R17 to 270-300 ohms 2-5 watt or parallel the 330 5 watt with another 1.5k ohm 2 watt (270 ohms)


6) That’s it now put it back together and be careful around high voltage always follow one hand rule working on tube amplifiers. The one hand rule is make sure other hand and body are not tied to ground other hand does all the probing. So tie meter or scope ground to the chassis ground then do all your measurements.

Other tweaks
From the way this amplifier is set up it may have had gain, tone and volume controls?
And they took the volume control out instead of the gain control so if you add a third 250k pot across TL01-B same as in the stock schematic this will be a gain control you should add a 27k resistor in series to set minimum gain at unity (1).

Lowest frequency amplified the stock value of C24 is to low 3db down at approx 270Hz the value in the mod is 47nF for 125Hz if you want you can go bigger 100nF but this may increase that annoying 60 Hz hum we have all come to love.
ERROR Should go with 100nF lowest frequency from guitar is 82Hz

On the pre emphasis mod you can change the value of R2 to increase or decrease the brightness of the maximum tone. Higher value for R2 (stock 100k) will reduce the maximum lower value increase it. If you lower the value you may want to increase the gain in the Op Amp stage to offset the loss.

Tone control pot from my results the tone is flat at the 9 o’clock position so if you use a 100k (125K) pot for the tone control this will move it to the 12 o’clock position.
Changing where the tone control operates you can reduce the value of C6 to raise or lower where the tone control operates but you should change the value of the cap in the pre emphasis circuit also (10nF across 33k ohm).
I just picked up a V5 for 20 bucks at a yard sale and wanted to try your mod,but the attachments seem to be gone.Can you repost them?

[jim p]

I found the mark up and picture to go with the no op amp modification that is part of posting #168. Here are links to them http://i1020.photobucket.com/albums/af330/vactube/noopampmodification.jpg http://i1020.photobucket.com/albums/af330/vactube/noopampmodificationschematic.jpg I would call or e mail Crate to get a PDF of the schematic for the amp. All the postings that now have no attachments are almost worthless, like a car repair manual with no illustrations, but it is what it is.

As always the stock speaker is junk and the output transformer is really a 16 ohm output. For more ideas on amp mods with postings you can try Sewatt

PS without the op amp to get a treble boost change the first cathode bypass cap C1 to a 470nf minimum voltage rating 16 volts.

[Infernie]

Hi Guys,

I have just laid my hand on a stock Crate V5 for a cheap price. I'm going to order a new speaker and some new tubes but i want to go even further with the modding. That's how i found this thread.

I've skimmed through the pages and decided the first thing i want to do is the Gain/Volume control mod of post #147. I hope i can find some pictures somewhere or else it will be a bit tough to do.

I've yet to decide wheter to do the no op-amp mod of post #168 or not. I don't know what i will gain with it? How does it influence my sound?

One more question: are there any mods i can try to get a good warm clean sound? I mean a sound like used in this clip:Youtube: Slow dancing in a burning room (http://www.youtube.com/watch?v=MpxoGtSUqkY) or a bit more crunchy like this: Youtube: Lenny - SRV (http://www.youtube.com/watch?v=_YIHvK5WN7I).

Anyone knows if this is possible with this amp and a stratocaster? What should i do after i did the gain/volume control knob mod? I plan to build a tubescreamer so my amp should do a good clean sound i guess?

Thanks in advance and i owe you much if you can answer my questions.

Keep on rocking!

*EDIT*

I found an interesting mod online. I tried to make the scheme out of it.

This is the orignial link: CLICK (http://www.tdpri.com/forum/amp-central-station/145636-want-crate-v5-schematic-2.html)
This is my scheme: CLICK (http://www.mediafire.com/?8c5uuerc7h9akz6)

Do you guys think this will work out and how will it work out soundwise?

[Christopher Whitlow]

Another way to modify the amp would be to use the tone pot for a volume pot and the volume pot for a gain pot. This involves no cuts just jumpers and removing components with one being replaced (C24)
1) Remove PCB from chassis
2) Remove R13 C26 C24( to replace with 47nf for more bass or keep as is if you wish) C6 C5 C4 and R27
3) Replace C24 with a 47nf
4) Jumper junction of C6 C5 and CW2 (tone pot) to junction of R27 and R15
That’s it now the volume pot will control the gain of 2nd stage op amp for overdrive and the tone pot will control the volume.

I introduced myself a moment ago in the newbie section.
Got this amp free on a trade with an Emminence Legend and JJ tubes. Really want to do this simple mod first, has anyone completed it yet? This is my first tube amp and it was free so what the heck right?
I only have one question, would a 12aT7 work for me to lower gain a tad? I just want a tad more headroom with a bit less gain. The loss of tone control doesnt really bother me, thats why I put nice CTS pots and treble bleeds in my guitars and my pedals all have tone knobs!
Jim and the others... wow! great info thanks so much for posting all the replies!

[tunghaichuan]

I only have one question, would a 12aT7 work for me to lower gain a tad? I just want a tad more headroom with a bit less gain.

Welcome to the forum.

If you want a lower gain 12AX7, try a 5751 or a 12AY7/6072.

The 12AT7 isn't a lower gain 12AX7, it has different specs and operation points. Other than sharing the same pinout and dual triode configuration, the two are more dissimilar than similar.

Having said that, there is nothing wrong with trying a 12AT7. It won't hurt anything, and who knows, you might even like the tone.

[Christopher Whitlow]

Welcome to the forum.

If you want a lower gain 12AX7, try a 5751 or a 12AY7/6072.

The 12AT7 isn't a lower gain 12AX7, it has different specs and operation points. Other than sharing the same pinout and dual triode configuration, the two are more dissimilar than similar.

Having said that, there is nothing wrong with trying a 12AT7. It won't hurt anything, and who knows, you might even like the tone.

Hey there! Thank you for giving me options to look into and thank you for the welcome.

[Chris Paul]

Just did this mod today and it was well worth the time and effort! Thanks a ton JimP :)

[Christopher Whitlow]

Sorry for the the post earlier, I was on a different account. The tone/volume mod is super easy and just what I needed. I am just learning the finer points of soldering and was a bit leery of the PCB board due to the small parts and all that. Well it went real easy with exception of clearing out solder on a couple spots. All my soldering experience has pretty much been guitar pots, switches, and repairing cables. Oh, and I can "sweat" a pipe too ;) I have a handful of very nice pedals and really dont need the amp to have tone control...for now. I am very pleased with how this amp sounds! I played every small valve amp I could get my hands on in the last couple years and this one was on the bottom of the list as far as sound quality goes. Now it sounds IMHO better than my friends stock Vox with tube upgrades by a long shot and I liked his amp a lot.

Now I have a follow up question of sorts. I feel as though the highs are too sharp even through my "darkest" guitar. I am wondering if there is a resistor or cap that can be swapped out to tame the "ice pick" a bit. I already have a home made treble blocker installed behind the grill, which does help, but I would like to run the amp with just a tuner and a wah and not feel like I need my EQ. Thanks again all who made this thread what it is!

[Christopher Whitlow]

Quick question about the sweep of the volume pot. I have done the above mod and now would like to know if there is a to slow down the sweep of the volume pot. This little dude is loud! Friend of mine uses my Cube 30x when he comes over and the 5watt tube is every bit as loud as the Roland. The amount of volume isnt really a problem, Its how fast it get loud that is hard to deal with. At 1 1/2 to 2 it starts coming on real loud and seems to top out at 7-9 on the dial. Can I use a different value pot like I have done in guitars or is this a more complicated fix? I really need to be able to play at actual bedroom volumes and I cant afford a hot plate so I am hoping I can slow down the sweep so that 0 thru 3 or 4 are usable in the house when others are watching the tube. Thanks all!

[tunghaichuan]

Quick question about the sweep of the volume pot. I have done the above mod and now would like to know if there is a to slow down the sweep of the volume pot. This little dude is loud! Friend of mine uses my Cube 30x when he comes over and the 5watt tube is every bit as loud as the Roland. The amount of volume isnt really a problem, Its how fast it get loud that is hard to deal with. At 1 1/2 to 2 it starts coming on real loud and seems to top out at 7-9 on the dial. Can I use a different value pot like I have done in guitars or is this a more complicated fix? I really need to be able to play at actual bedroom volumes and I cant afford a hot plate so I am hoping I can slow down the sweep so that 0 thru 3 or 4 are usable in the house when others are watching the tube. Thanks all!

The problem with the pot isn't the value, it's the taper. If your volume is coming up to fast, then it is most likely a linear taper pot. What you want is a log or audio taper. It may or may not be hard to find in the right value. What is the value?

[jim p]

I wish the schematic mark ups were still on line, oh well. I should remember the mod, but it has been awhile. I don’t recall if the tone pot is a linear or audio (log) taper but there is way more signal across it then required you could parallel it with 25k to 50k ohms. The mod was to just use what you have with no new parts required. As far as ice pick tone I think just having an op amp as the input stage causes a brighter and colder tone from the amp. You could try adding some feedback capacitance on the first tube stage say 33pf to 100pf from the plate pin 6 to the control grid pin 7.

[Christopher Whitlow]

Thanks guys! I'm not afraid to add a resistor or change the entire pot. I did this after practicing on junk toys and have since installed a Keeley type mod in my DS-1 and "true" bypassed my CryBaby. Turns out a friend of mine is really good at soldering and gave me some great pointers so now my parts come out clean and get good connections MOST the time :) At this point my biggest biggest problem is lack of knowledge, I was all proud because I remembered that resistors in series add up in value lol!
Jim, when you say to parallel the pot with 25-50k is that a resistor across the pot lugs? If so thats way easy to check out while I look into the taper. I have CTS and Alpha pots lying around but mostly all of them will be 250 500k A&Bs for my guitars so if the amps pot is labeled with a low value can I just replace with a higher value audio pot?

I know these are way newb questions and I appreciate you guys still checking in on this thread. Any suggested reading/study material for an intelligent mechanically inclined older gentleman to learn from? I found resistor charts and schematic keys and studied PCBs to see the power flow and I sorta get it but think an "electronics for dummies" sorta thing might be in order.

[tunghaichuan]

I know these are way newb questions and I appreciate you guys still checking in on this thread. Any suggested reading/study material for an intelligent mechanically inclined older gentleman to learn from? I found resistor charts and schematic keys and studied PCBs to see the power flow and I sorta get it but think an "electronics for dummies" sorta thing might be in order.

Here is the motherload of tube amp related books:

Peter Millett's Tech Books Online (http://www.tubebooks.org/technical_books_online.htm)

There is enough there to keep you busy for a long time.

Here is another good book to start with:

Jack Darr's Guitar Amplifier Handbook (http://www.diyguitarist.com/Misc/J_Darr.htm)

This is a good, basic intro to tube amps. It was written in the 60s and later expanded in the early 70s so there is no discussion of FX loops, channel switching, or distortion circuits, but it covers the basics of how tubes and amps work, and how to fix them. It is also available in print, and it is well worth it to have a hard copy as the above .pdf files only are about half of the book. The other half is a bunch of 60s and 70s era tube amp schematics, which make the book well worth the price.

[jim p]

Yes just put the resistor across the two outside lugs of the pot to parallel it. I looked at the schematic and originally the signal to the second tube was across a 10k resistor so with adding the resistor in parallel with the 250k pot the resistance will be 22k or 42k so still more signal but closer to the original level before the mod. If you don’t have a schematic for the amp just call Crate (Loud Technologies) and they will e-mail you a PDF.

[Christopher Whitlow]

Here is the motherload of tube amp related books:

Peter Millett's Tech Books Online (http://www.tubebooks.org/technical_books_online.htm)

There is enough there to keep you busy for a long time.

Here is another good book to start with:

Jack Darr's Guitar Amplifier Handbook (http://www.diyguitarist.com/Misc/J_Darr.htm)

This is a good, basic intro to tube amps. It was written in the 60s and later expanded in the early 70s so there is no discussion of FX loops, channel switching, or distortion circuits, but it covers the basics of how tubes and amps work, and how to fix them. It is also available in print, and it is well worth it to have a hard copy as the above .pdf files only are about half of the book. The other half is a bunch of 60s and 70s era tube amp schematics, which make the book well worth the price.
Huge thanks!

[Christopher Whitlow]

Yes just put the resistor across the two outside lugs of the pot to parallel it. I looked at the schematic and originally the signal to the second tube was across a 10k resistor so with adding the resistor in parallel with the 250k pot the resistance will be 22k or 42k so still more signal but closer to the original level before the mod. If you don’t have a schematic for the amp just call Crate (Loud Technologies) and they will e-mail you a PDF.
Going to remove op amp per your instructions around post #160 or so. Wish I would have been doing this when the topic was fresh but here goes another question... will the op amp removal adversely affect the volume/gain mod. I'm looking at the board and my untrained eye says no but wouls hate to do it and wind up at full volume because I read the traces wrong! I really think the answer is no but want to make sure because this thing makes me nervous now that I know how careful I have to be with it. I never should have started reading, these things hold a lot of voltage!!!!!
EDIT: My bad, meant to say thank you for your help!

[jim p]

If you do the mod at post #160 the stock volume pot will be a volume pot again and the tone pot will be a tone pot again with C6 installed. So you won’t have the volume pot acting as a gain control while you have the tone pot acting as a volume control as you do now.

[Christopher Whitlow]

If you do the mod at post #160 the stock volume pot will be a volume pot again and the tone pot will be a tone pot again with C6 installed. So you won’t have the volume pot acting as a gain control while you have the tone pot acting as a volume control as you do now.

Very nice! I was seriously considering trying to install a gain pot now in addition to the volume and tone. Im looking over the old posts and studying the layout of the amp and sounds/looks fairly simple to put one in. This is an awesome learning platform! I will keep reporting my progress in case others are still interested in the mod :) I have some new soldering tips coming and I think I will wait on those. The shovel head of a tip that came with mine is hard to get into those small spaces.

[Christopher Whitlow]

Figures! I have no output but do have a very slight hum that is barely audible. I looked over all my joints and all looks OK. Could it have anything to do with my previous volume/tone control mod?

[jim p]

Here is a list of things to check and ohmmeter to see if the connections are correct.


With the op amp out you should have C24 C25 and C26 removed with a jumper from pin 3 of the op amp to the junction of R1 and R2 with R2 removed. That is the signal from the guitar to the first triode. Pin 7 of the op amp should be grounded C27 removed R27 should be removed with a jumper from the junction of R27, R7 and R15 jumpered to pin 6 of the op amp. C6 should be installed R15 should be installed. If you ohmmeter from the tip of the ¼ inch jack to pin 7 of the 12AX7 you should read the value of R1 47k also check to ground should be 1 Meg. Ohmmeter pin 2 of the 12AX7 to ground you should have zero with volume pot turned down to 250k at volume at full clockwise. From pin 2 of the 12AX7 to R9 should read approx 500k to 600k.

Another source for amp modifications and help is over at sewatt.com

[Christopher Whitlow]

Here is a list of things to check and ohmmeter to see if the connections are correct.


With the op amp out you should have C24 C25 and C26 removed with a jumper from pin 3 of the op amp to the junction of R1 and R2 with R2 removed. That is the signal from the guitar to the first triode. Pin 7 of the op amp should be grounded C27 removed R27 should be removed with a jumper from the junction of R27, R7 and R15 jumpered to pin 6 of the op amp. C6 should be installed R15 should be installed. If you ohmmeter from the tip of the ¼ inch jack to pin 7 of the 12AX7 you should read the value of R1 47k also check to ground should be 1 Meg. Ohmmeter pin 2 of the 12AX7 to ground you should have zero with volume pot turned down to 250k at volume at full clockwise. From pin 2 of the 12AX7 to R9 should read approx 500k to 600k.

Another source for amp modifications and help is over at sewatt.com

You are awesome! I know already that one problem will be me not realizing I interrupted the flow when I did the second mod by NOT replacing c6 or c15. Amazing what you miss when you dont know what to look for. I have a multi meter and will check values at those critical points a Bnd replace my missing parts in the signal path then report back. I have the book mentioned above on it's way and Im learning a bunch from the pdf that explains amps in the 70's and before. When I recieved this amp free I decided this was my chance to learn how they work and boy howdy am I a learnin! Thnx again folks!

[vinyl_key]

Hey all, proud owner of a V5 that I modded per post #168 ~2 years ago with a few questions after re-reading all 23 pages of this thread :poke:

My current set up for my Crate is: op-amp removed and stock 12AX7 replaced with a 12AT7.

• What are some ways to make the tone control act like like a normal tone control. I've seen mentions of changes to the tone stack in this thread, but they're a bit hard to follow what's going on with more than half of the images gone.
• Will a Weber Signature AlNiCo 10 fit in? The depth is longer than the 4" that will fit, but it looks like the magnet (with the cover removed) is skinny enough to just stick past the amp enclosure. If the AlNiCo doesn't fit, a Sig ceramic will make do.

Thanks for the wealth of information in this thread

[jim p]

The Weber AlNiCo will fit without the shielding around the magnet. You could consider the Eminence Legend 10516 as a speaker choice also. The output transformer impedance is really 16 ohms so you may want to get a 16 ohm speaker. On the tone control if you remove C5 and C4 and change C1 to 470nF then the tone control will be set to bass at CCW and treble at full CW. The op amp used to boost the treble so to make up for that changing the first triode bypass cap to 470nF will make up for not having the op amp boost.

[SciHi]

• What are some ways to make the tone control act like like a normal tone control. I've seen mentions of changes to the tone stack in this thread, but they're a bit hard to follow what's going on with more than half of the images gone.


Since the stock tone pot has the wiper to ground, I converted it to a Marshall normal channel tone control. I can post a partial schematic for this mod when I return home after the 4th... http://mhuss.com/18watt/schematics/18wattLite.gif

OK, maybe this will help. http://s615.photobucket.com/albums/tt237/scihibmxer/v5marshalltonemod.jpg

[SciHi]

I was talking with Rock Mumbles this evening and he reminded me of the power tube fixes for this amp. First, the screen resistor needs moved to the correct position, then the EL84 bias needs corrected, depending on the size of the cathode bypass cap, 240-270R cathode resistor. I also added a master volume but it is not necessary...

http://s615.photobucket.com/albums/tt237/scihibmxer/v5el84modsmv.jpg

[rock_mumbles]

I was talking with Rock Mumbles this evening and he reminded me of the power tube fixes for this amp. First, the screen resistor needs moved to the correct position, then the EL84 bias needs corrected, depending on the size of the cathode bypass cap, 240-270R cathode resistor. I also added a master volume but it is not necessary...

http://s615.photobucket.com/albums/tt237/scihibmxer/v5el84modsmv.jpg
I used a 240 ohm cathode resistor and wish it was still a bit smaller, although I do have a 100 ohm (not-a) sag resistor that drops a few volts. My plate voltage is now 297V and the screen is 289V, prior to reworking the dropping resistor and screen resistor the screen was about 310V and the plate about 300V ... not good ...

I love this amp with the circuit I now have in it, I pulled the minimum number of parts to be able to rework the circuit.
First I pulled both pots, the stock op-amp gain control for the volume control ??? what were they thinking, and the tone pot mess, although if you want to leave the tone pot in circuit it can be rebuilt to the Marshall 18 Watt "normal" tone control, which works really nice for a Marshally V5.

I pulled R1, R9, R10, R15 and R27. I cut R7 as it's mounted on top of the socket (it might not be a bad idea to cut D9 and D10, so theres no power to the op amp even though it's not connected to anything anymore)

The easiest way to redo the input to bypass the op amp and associated circuitry is to jumper R10 and run a 68k (or less) resistor from the right R10 via (pcb hole) to the top R1 via, closest to C1. You should be able to place the input resistor lead into the right R10 via and bend the lead over and up into the left via to form the jumper. I put insulation tubing on the exposed input resistor leads.

For V1a, R3 gets switched to a 2.7k and C1 to a 0.68uf (film)

V1b is fine stock

R17 the EL84 cathode resistor is way too large at a 330 ohm it should be about 240 ohms.

Instead of just moving the screen supply like SciHi showed above, I replaced R25 with two resistors in series, put two 2.2k 2 watt resistors in series one leg goes into the R25 via (pcb hole) closest to C16, I put the other leg into the left via labeled R23 (unused) then I connected the left leg of R18 (screen resistor) to the junction of the two 2,2k resistors.

Then for the tone control/volume pot, I used the Framus mid control with a 500k Audio volume pot. The left via of R9 (closest to C2) is used for the tone control input and the volume control output connects to the left via of R27
here's a schematic of the tone/volume control ...
http://rh-tech.org/public/Framing_Leah_tone-volume.png

[bcdon]

That is some serious hacking, very interesting!

[rock_mumbles]

It's completed, to tame the highs a bit I ended up putting a 680pf cap across R6, that did the trick.

I pulled the Weber Ceramic Sig 10 (smooth cone) and replaced it with a new Jensen C10Q I picked up for $20 ... I decided I wanted to keep the Weber Sig 10, it sounded a lot better in the Crate combo cab, fortunately the Framus mid control deals with the boxy heavy midrange tone of the Jensen pretty well.

The Weber Sig 10 is a nice affordable speaker for the Crate V5, it sounds really good in the small Crate combo cabinet. With my Strat the Jensen C10Q (which has a larger magnet and just barely fits) has a bit too much of a midrange dominant tone (for me) ...

I agree with jim p that the Eminence 1058/10516 series speakers are really nice sounding, it was the best sounding speaker we tried in my brother's Vox AC4TV ...

[Will Muhovich]

[QUOTE=So what I did is to cut some traces and add some jumpers to make it an all tube amp. After the input resistors (1.5Kohm and 1 Meg) I cut that trace going to the input of the op amp and sent it straight to the first tube grid and cut away any other parts that were there that might have influence. I decided that the tone control was not a bad thing, just different- and I left it as is. Since I now had a 250Kohm volume pot out of the circuit, I put that between the tone circuits and the grid to the second triode in place of the attenuation scheme that was there and to maintain grid to ground loading and control. I cut the traces around the volume pot and ran jumpers to the appropriate places (the pot connects to the output of the tone circuit, the two lower resistors were cut out, and the other end of the pot was run to ground. The wiper fed the second triode's grid.

Deafelectromark (alias manoteal):rockon:[/QUOTE]

So, I love the ideas presented here, and I know it's been a while since you posted this, but is there any chance you have a better schematic with illustrations or notes added, and/or gut shots of the mods as described? I may try the easy mods you suggest first and replace the speaker, but this sounds like it might be easier than getting or making a tweed princeton clone out of the little bugger. Not that there's anything *wrong* with that, just typing it makes me think 't was a good plan, don't give up on it now...

Anyway, any hints or tips you'd care to share would be greatly appreciated.

Thanks!

Edit: Noob mistake. Epic fail?! I only just noticed that there's like 24 pages to this thread going right up to the present day and I may need extensive review of the other 23 pages before I start cutting traces. But I might anyway. We'll see...

[rock_mumbles]

...

Anyway, any hints or tips you'd care to share would be greatly appreciated.

Thanks!

...

Here is a schematic of the modification I discussed above, it's similar to Deafelectromark's mod except I wanted to re-voice the preamp, replace the tone control with a mid-cut tone control and instead of cutting the traces to the volume pot I pulled it from the pcb (be careful if you aren't familiar with pulling components or you'll end up with a damaged pcb)

http://rh-tech.org/public/Crate_v5_Framing-Leah.jpeg

If you want to keep the stock tone control only remove R15, R27 and R7 (I just cut R7 out) from between the two stages. The volume control input (clockwise lug) connects to R15 where it connects to R29, the volume control wiper connects to R15/R27 junction, the volume control ground connects to the ground via on R27.

[vinyl_key]

Thanks for the info!

Got my Weber AlNiCo Sig10s in the mail today, sounds much better! Can't wait till the speaker gets fully broken in. Now all that's left is to get the tone circuit to my liking.

[Maarten Aerts]

Found this thread again today.
signed in to share my results with the V5.
(Intro: played bass for 35 + years and home guitar, but recently tried to play guitar in a band because i got this amazing Epiphone dot studio es335. And it's fun to rock.)

Also bought the crate v5 about six months ago, and found the modding fora....

The mods described here were way to scary :)
I instead did the following, combined from other fora:
Changed the speaker with a Celestion tube 10.
Changed the tubes:
1 x JJ EL84 / 6BQ5 Matched (TF-0987)
1 x JJ 12AX7 / ECC83S (TF-3645) (also tried others, not nice)
Replaced R17 with a 150watt 5 ohm resistor because the bass distorted ugly .

Loved the sound, wished it could get louder to play on stage.Use it every day at home.

The amazing thing is, my marshall jcm900 4501, was always failing when played on higher volume.
The store were i bought it couldn't find the problem, so i kept in as a home practice amp. (to shy to make a big noise about warranty those days)
On low volume it was exellent, but totally unreliable for stage.

And now i finaly had dared to solder on an actual tube amp (R17)- i had the courage to open up the marshall and found out that the pins of the things the tubes go into weren't soldered right.
If really hot, they would lose contact....
Now a have my big amp again and a really nice little V5, thanks to these fora.
love it with its cleanish blues tone and distortion with a carl martin pedal.

And after re-reading all these pages i think i will do the no-op amp mod.
I understand a lot more now :)

Hope i won't spoil it :)

[Maarten Aerts]

Since the Crate was to have more output with 16 ohm, i put some input-jacks together to make plug 2 x 8 ohm speakers out, and 16 ohm in.

Tried the celestion of the marshal with the internal tube 10 (crate), it is amazing, so loud! With the 335studio it made the tonepot usefull, jazz, blues.Pedals worked great.
Way to loud for home-use. but full sound.
With my 10" swr-basscab it was also really loud, and a nice sound, but not as much big warm open in the lows.
So i need a 12" cab with 75/100 watt celestion G12 and the jacks wired for 16 ohm, no need for soldering. (A Jensen would be to much mid-high i think)
Thanks again for the valuable info :)

Back to playing now

[cebreez]

Hello All!! My name is Terry Smith.... I am a new member to this forum but I've been pouring over it for weeks. Have had my Crate V5 for at least as long as this thread has been up and it has actually seen very little use since I regularly play through a Peavey Classic 30 1x12 even when I practice. Though lately I've wanted to have a more portable setup when away from home so I got the old Crate back out in hopes of modding it a bit. This is a great thread and jim p you are my hero.... BUT!! Here is my quandary.... I want to keep the op-amp.... Round out the tone.... and increase the headroom. I've liked some of the mods that move the volume pot and deal with the tone knob... I know Im behind but (why?) would we have the tone controlled by the op-amp to start with...? Would it not serve better after the op-amp......? If this all sounds confusing it is because I am very confused!... (and going blind :) ) I actually found an old 10" speaker from an Alesis Wildfire I had laying around... It fit after some coaxing but made a huge difference in tone and headroom. Now I am ready for new tubes and whatever mods you fellas deem absolutely necessary to capture of little more of that Fender magic. Any help would be GREATLY appreciated.

P.S. Im not scared to mod anything. Just want to make sure its worth it in the end.

Thanks
Terry

[cebreez]

Is this thread dead? HELLOOOO!!!

[SciHi]

Is this thread dead? HELLOOOO!!!

HELLO and welcome. Jim P. had posted very early some fixes if you want to keep the opamp, I think most of use just removed it and modded from there... It is hard to get much headroom, at any volume, out of a single EL84. You can get good overdrive and it will get loud when the EL84 is being driven hard but none of the little 5 watt single end tube amps have much for clean headroom. The speaker is probably the biggest single improvement to the amp, in my opinion, the most important first mod. My experience is the tubes have much less impact, unless you want to run a lower gain tube such as a 12AY7. Put in a decent speaker, and keep the gain turned down and it should at least be usable.

[cebreez]

Thanks SciHi! I was feeling really alone in here! I understand what you are saying. I didn't see jim p's earlier post and what I'm finding out is the older post seem to lose there pictures. Could just be my crappy computer though. I understand what you are saying but let me interject with a personal observation and please feel free to call me foolish. Like I said I know just enough to be dangerous. I built successfully the "Noisy Cricket" amp and at first was very pleased till I realized for old deaf ears it just was not loud enough and broke up way too soon. I know why and thats okay but before I took the soldering iron back to it I did a little test and plugged it into my pedal board to see how close it was to an overdrive circuit. It just made everything louder, much much louder but did not overdrive or distort the signal at all. Why.... ? My point is I believe the op amp circuit in the Crate V5 is doing exactly the same thing. It is not there to overdrive the preamp tube just to compress and amplify the input signal giving us more headroom. When I changed out speakers I got phenomenal results from a relatively cheap speaker with a bigger magnet. Now i would like to use the input circuit(the op amp) and extend the frequency range (more lows and highs) on command with a better tone circuit. I like the op amp because there is so much you can do in that little space and never have to touch the tubes or drive circuit. Like putting a performance chip in your car or cleaner gas and getting better performance without having to crack open the engine. I hope all this makes sense.... it does in my head but then again that is another matter. HA!

Thanks SciHi....

[cebreez]

P.S. I saw jim p's original post but none pictures were there to show what he did. The guy really knows what he is doing but I had a hard time following his explanations. I wish I had been a member then and gotten into the discussion. I believe he was on the right track but I would have loved to coax him into a different direction. When I get this figured out and eventually I will, I will do my best to post the schematic markups. I totally disagree with the "sledgehammer" idea. This amp is a real sleeper and has almost everything you would find in amps costly "x infinity" more. I am thinking too about a different output transformer to boost this to a 10 or 15 watt amp but haven't gotten past the input circuit yet.

[tunghaichuan]

P.S. I saw jim p's original post but none pictures were there to show what he did. The guy really knows what he is doing but I had a hard time following his explanations. I wish I had been a member then and gotten into the discussion. I believe he was on the right track but I would have loved to coax him into a different direction. When I get this figured out and eventually I will, I will do my best to post the schematic markups. I totally disagree with the "sledgehammer" idea. This amp is a real sleeper and has almost everything you would find in amps costly "x infinity" more. I am thinking too about a different output transformer to boost this to a 10 or 15 watt amp but haven't gotten past the input circuit yet.

You might have to replace the power transformer as well as the output transformer. Boosting the amp from 5 watts to 10-15 watts is not as easy as it might seem. There are several ways you could go about it.

You could add another EL84 in parallel to give you 10 watts, but you'd have to use an output transformer with half the primary impedance as the existing unit. You'd have to replace the power transformer with one that has double the current capacity as the stock unit.

If you wanted to move up to a larger, single power tube, you could probably get 10 watts out of a 6L6GC tube in SE. But again you'd have replace both stock transformers with appropriate new units.

For 15 watts in SE operation, you'd need to go to a 6550 or a KT88.

All of the above are for single ended operation, and the larger the tube, the heavier the transformers get to handle the increased current. These transformers also tend to be very expensive.

You could completely gut the amp and build in a push pull circuit using two EL84s or 6V6s. But then you have to add a phase inverter to operate the amp in push pull. This is in addition to the existing preamp circuit. The transformers would be smaller and lighter, but the question is: do you have enough room in the chassis for the extra circuitry?

Modding a 5W amp into a 10-15 watt amp is not an economical way to get a killer practice amp. Really, you'd be better off buying a commercial amp that already has the features you want.

[cebreez]

I totally get what your saying and all options that I have considered. Wasn't thinking about the power transformer, good point. Definitely not enough room to start adding more tube circuitry. Larger tube...? Well...? Maybe. Expense is definitely the issue. I have a larger tube amp but not really wanting to go that route. Want to keep this one small and compact. Played with my BBE Sonic Maximizer in front of the Crate today and love the tonal difference it made. Gave it clarity and very nice harmonics. Liked it so much I ordered a pcb for a look-a-like on "madbeans.com". Might try to incorporate that on the input or in place of it. Also considered a nice 4 knob preamp pedal circuit for the same reason. Would add the necessary gain and EQ on the front end while still keeping it clean and low noise.

[cebreez]

I know a couple of good pedals in front of the Crate would probably do more for the tone than all my tinkering but I really want to keep this thing portable with no extra pedals to carry or plugs to plug in.

[SciHi]

... Now i would like to use the input circuit (the op amp) and extend the frequency range (more lows and highs) on command with a better tone circuit. I like the op amp because there is so much you can do in that little space and never have to touch the tubes or drive circuit. Like putting a performance chip in your car or cleaner gas and getting better performance without having to crack open the engine. I hope all this makes sense.... it does in my head but then again that is another matter. HA!

Bent on keeping that opamp, well check out Verne's posts over at HC, "Supercharging a V8." http://acapella.harmony-central.com/showthread.php?1519445-Supercharging-a-V8

The V8 is the V5's big brother. First thing Verne did was put in a high quality chip! Replaced the TL072, check it out, and Verne is still around and could help out keeping the opamp intact. You can compare the schematics and see where the V5 cut a few corners to "cheapen" up the amp.

Here is a favorite quote of Verne's:

"The problem with the opamp implementation as found on the V8 – particularly the hiss and extremely low amount of clean headroom – isn’t the USE of an op-amp, but the CHOICE of op-amp. The TL072 is a cheap [20 cents in quantity] component that probably introduces as much noise as using a tube, so it defeats the purpose. Because of its low headroom, it actually introduces a bunch of noise that keeps you from really cranking the gain to its sweet spot.

The “fix” is to replace it with a TLE2072. This is one of Texas Instruments Excalibur series and is renown for being the best of the best. You can get this chip from Mouser for around $2.50. The only complicating factor is that SLM soldered the TL072CN to the circuit board."

[cebreez]

Awesome.... Im checking it out now! Thanks SciFi!!

[jim p]

A big problem for headroom in the V8 is the power supply for the op amp is only +/- 8volts so you can have clipping with low gain on the op amp. The V5 has +/-15 volt rails and you could up them to +/- 17 to 18 volts no problem if you want. I think any op amp is going to change the tone with approx 30 transistors and feedback inside the op amp it is not the same as going straight into a tube. The V5 is the V8 but using the gain control as the volume control and removing the volume control and line out.

[cebreez]

Yeahhhh.......... well....... :thwap I totally agree with you!!! I really do! Does make you wonder why the "geniuses" put it there to start with. Seems like a big waste of time and money. Honestly in the end I will probably do exactly what you are suggesting but in the meantime Im going to see what kind of fun I can have with this. Like you did...:)

[cebreez]

Anyone wanting to relive this discussion. Im starting my mods any day now. The new thread will be here: http://www.thefret.net/showthread.php/19149-Crate-V5-quot-MODS-quot-will-commence!

[nbs2005]

Hi, Trying to bring this back from the dead. I want to do the mod described by deafelectromark which is about the skill set I have. (OK, that might be more than I have). I'd really like to see some of the pictures that were posted for that back in the day and are now dead links. It would really help me in my project.

BTW, this has been a great thread.

[marnold]

Hi, Trying to bring this back from the dead. I want to do the mod described by deafelectromark which is about the skill set I have. (OK, that might be more than I have). I'd really like to see some of the pictures that were posted for that back in the day and are now dead links. It would really help me in my project.

BTW, this has been a great thread.

I think you may be out of luck since he hasn't visited The Fret in over seven years. You could try emailing him via his profile and hoping against hope that he has the same email address.

[nbs2005]

I sent him an email. It did not bounce, but I haven't heard anything back either. If anyone has done this mod and is still on the board, I'd greatly appreciate a picture of the work done.

Thanks,

J

[nbs2005]

Hey all, one more update. I took the v5 to Steve Moratto, he's an amp builder in Ajax just outside of Toronto. For $125 Canadian, he turned this into a pure tube tone monster. That included new pots. He's a great guy with a great reputation in Ontario. You can reach him here http://www.morattoampshop.com/ And no, I'm get nothing for this; just wanted to promote a fellow Canadian.