Crate V5 mods... anyone?

[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.
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/...matic31210.jpg

The layout is here
http://i1020.photobucket.com/albums/...rbpcb31210.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

[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/...dmodulepic.jpg

http://i1020.photobucket.com/albums/...dmodulepic.jpg

http://i1020.photobucket.com/albums/...verbPCBpic.jpg