Marshall JVM 410H modifications!

[deeaa*]

Just finished modding my JVM and I gotta tell you...highly recommend them for any JVM player. Man they woke the thing up.

1st of all, all thanks to jvmforum.com guys who had awesome guides and whatnot to help.

I liked the JVM just fine; the D/I sound in particular is great, but the sound from speakers had some shortcomings compared to classic Marshalls. Still, as a compromise for live playing it sure is a great amp also stock.

Basically, the amp has preamp sections from many a classic Marshall, JTM thru JCM series, but I suppose both to keep the costs down and to keep the amp as versatile as possible and playable at very low levels too, they have made some compromises.

The most notable ones are the lack of choke, which is one of the reasons making the amp 'tight' and not very organic at all. Instead it has just a resistor for the job. Also, the amount of negative feedback is quite high stock, which kind of keeps the poweramp always in check and not roaring free, and that makes the amp sound a little cold and 'stiff' for lack of better word.

Third issue is the overall tone is more geared for modern metal sounds, and can be a bit too bright and even brittle for higher notes.

So here's how to rectify them:



First you open up the chassis - having made sure you've drained the caps. This can be done by switching the amp off and then switching Standby on despite it's off and wait for a while, minutes will do. But best measure with a multimeter that it's drained once you get the chassis out. When you look at the board, at one end there's four big caps; measure the leads of the resistors between/in the middle of those that they're empty.

Unscrew the jacks, the D/I jack screws, and remove the tubes and their holders. Label the tubes so you can put them back in the same order.



Then remove the board screws and that L-shaped guard by the said caps. Mark the leads so you can find the right spots once it's done, naturally. The tube-like connectors you just pull up, and the flat white connectors you kinda wiggle left-right-left till they come loose.

The hard part is to squeeze the board out of there. It is VERY tight. The trick is to press from below by the tube sockets so that you start from the left, push it in (I know; it feels absolutely impossible it'll ever push far enough) and WHILE you keep them pressed in, press the next one, the next...going right towards the caps, and keep the board supported so it doesn't fall back. It's tough. Do that a few times from left to right, keep pushing it in and don't let it fall back, and then you get first one socket thru and then the rest. Getting it back is hard too, but similarly inch it in slowly.



It's easier to check from the inside where to position the proper choke. I used a Hammond one, 4 Henrys. I understand anything from 2,5 to 10 or even more will do. 200-400mA. Chokes are cheap, this one was 19€ only.

Drill three holes, two for the choke and one for the leads going through.



There's plenty of room there. Position it as close as possible to the main caps; the resistor to be replaced is the white rectangle just left of those caps. R106. The board is well labeled. Get some locking agent for the screws too :-)



Choke installed...well enough room for sure!

Solder the choke leads last; now for the 'Plexi' mod that'll eliminate those nasty too-high squeals when rippin' it:



Solder a .68uF or 1uF polyester capacitor in parallel with R97, i.e. just solder it next to it/over it.
Like so. I used some hot glue to secure it with a few dabs to caps nearby, and shrink wrap on the wires.

Next up, let's fix that insane negative feedback amount:


Replace R58 with a suitable resistor. JVMForum gives these guidelines on what values to use for what effect:

R58 = 47k -- late '60s Plexi
R58 = 74k -- early '70s MkII Plexi
R58 = 82k -- stock JVM
R58 = 137k -- EVH's Plexi
R58 = 176k -- JCM800 2203
R58 = 177k+ -- a Marshall with almost a Vox's lack of headroom in the power amp

I myself went for 180k because I love me Marshalls with no neg feedback, untamed :-) (My Ceria also had a switch to make it have pretty much no feedback and I liked it that way).

Now when those are done, remove the R106 resistor and solder the lines from the choke there instead. Best do it last, because likely the choke leads aren't hugely long. And I hope you put the choke somewhere close :-)



Like that. Here you also see the resistors between the caps that you can measure from if the caps are drained.

That's it!

I screwed up my before/after clips, but here's some going thru sounds after. Recorded with a (NB): single-EMG85 equipped superstrat/metal axe...so the cleans aren't exactly clean and the bridge pickup only of course is what it is. But who needs neck pups with an EMG85 :-)

I REALLY REALLY REALLY can't tell you how much I love the changes.

Immediately it was apparent the amp was a bit louder and touch more gainier, so I had to lower my channel volumes just a touch, and some gain too. But MAN it sounds so much better.

The clean channel is now just like a Bluesbreaker. You hit chords, they just BRAMMM out there with utmost Vox-like clarity and punch, and there's WAY more pant-flapping lower sound content. Kinda like someone put in bigger speakers. That's mostly the lack of negative feedback I guess.

The 2nd clean is instant pure old ACDC. Just like a hotrod Plexi. Warm and big, too.

Drive 1 is now exactly Iron Maiden on The Number of The Beast etc...and perfect for any rockin'. JCM800 at its best.

Drive 2 is now way more loose and usable, growls almost like a Mesa or something, and screams in solos. Nicely there's now even a touch of slight sloppiness and growl where there used to be tight upper-middy bite. And even the craziest bends don't grate on ears now, even without picking and just hammerons it's instant Gary Moore and sustain 4 ever.

Here's some sloppy playing after the mods, going from cleaner towards the hotter channels.

http://deeaa.pp.fi/clips/JVM_MODDED.mp3

[Robert****]

Wow, that is interesting! Thanks for posting.

I would like to have that done to mine, but I'm worried about doing that myself...

[deeaa*]

Tell you what, Robert...I was a bit scared to start it. Nearly lost my nerve. But in the end it wasn't hard at all.

What you could start with is just simply remove C83 completely, and solder that Plexi cap parallel to the R97.

Removing C83 is what the amp designer Santiago suggested himself:

"Removing C83 on the board will be the solution for what you are after. Just snap it off of the pcb and both gain and treble response are lowered while retaining the bite and not getting muddy. I also think that the gain control will be more usable in all its range and those modes more dynamic"

I left that one for later, if these would not be enough.

But the point is, those two mods will change it a LOT and for the C83 removal you need not even solder, and for the plexi cap all you need to solder is attach the new cap parallel to the resistor, two small points of solder and not even need to remove the board. Hardly harder to do than biasing the amp! Maybe you could start with those? But do check JVM forum first for whether the designations change between the combo and head boards. I don't think they do, tough.

I think the next time I need to bias I'll snap the C83 too. Although I'm pretty damned happy with the amp now after the mods; the speaker sound is finally on par or actually much better even than what I've been getting from the D/I.

[Ch0jin]

Nice job! Seems like the perfect Marshall the way you describe it.

[Duffy]

Totally nice playing and a lot of great sounds. Seems like the recording couldn't capture it all and I'm sure it sounded better live. I like the range of sounds you get out of that.

[Robert****]

I like the tones. How did you record?

What colors did you use? The cleanish in the beginning is nice. Sounds like orange? Is the next channel, the Back in Black riff stuff, the Crunch on green?

[Robert****]

And where and what is the C83? Is it a resistor?

[deeaa*]

c would be a capacitor. they are VERY clearly marked and grouped with like numbers close by.

As for modes, I'm fairly sure clean is red - I found I like it better in a hotter mode but gain down than lower mode and gain up. the second must be amber amd od1 amber too, lead is red.

Recorded with zoom stereo Mica maybe 3-4 feet from the amp and a little sideways.

[Ramo]

Just finished modding my JVM and I gotta tell you...highly recommend them for any JVM player. Man they woke the thing up.

1st of all, all thanks to jvmforum.com guys who had awesome guides and whatnot to help.

I liked the JVM just fine; the D/I sound in particular is great, but the sound from speakers had some shortcomings compared to classic Marshalls. Still, as a compromise for live playing it sure is a great amp also stock.

Basically, the amp has preamp sections from many a classic Marshall, JTM thru JCM series, but I suppose both to keep the costs down and to keep the amp as versatile as possible and playable at very low levels too, they have made some compromises.

The most notable ones are the lack of choke, which is one of the reasons making the amp 'tight' and not very organic at all. Instead it has just a resistor for the job. Also, the amount of negative feedback is quite high stock, which kind of keeps the poweramp always in check and not roaring free, and that makes the amp sound a little cold and 'stiff' for lack of better word.

Third issue is the overall tone is more geared for modern metal sounds, and can be a bit too bright and even brittle for higher notes.

So here's how to rectify them:



First you open up the chassis - having made sure you've drained the caps. This can be done by switching the amp off and then switching Standby on despite it's off and wait for a while, minutes will do. But best measure with a multimeter that it's drained once you get the chassis out. When you look at the board, at one end there's four big caps; measure the leads of the resistors between/in the middle of those that they're empty.

Unscrew the jacks, the D/I jack screws, and remove the tubes and their holders. Label the tubes so you can put them back in the same order.



Then remove the board screws and that L-shaped guard by the said caps. Mark the leads so you can find the right spots once it's done, naturally. The tube-like connectors you just pull up, and the flat white connectors you kinda wiggle left-right-left till they come loose.

The hard part is to squeeze the board out of there. It is VERY tight. The trick is to press from below by the tube sockets so that you start from the left, push it in (I know; it feels absolutely impossible it'll ever push far enough) and WHILE you keep them pressed in, press the next one, the next...going right towards the caps, and keep the board supported so it doesn't fall back. It's tough. Do that a few times from left to right, keep pushing it in and don't let it fall back, and then you get first one socket thru and then the rest. Getting it back is hard too, but similarly inch it in slowly.



It's easier to check from the inside where to position the proper choke. I used a Hammond one, 4 Henrys. I understand anything from 2,5 to 10 or even more will do. 200-400mA. Chokes are cheap, this one was 19€ only.

Drill three holes, two for the choke and one for the leads going through.



There's plenty of room there. Position it as close as possible to the main caps; the resistor to be replaced is the white rectangle just left of those caps. R106. The board is well labeled. Get some locking agent for the screws too :-)



Choke installed...well enough room for sure!

Solder the choke leads last; now for the 'Plexi' mod that'll eliminate those nasty too-high squeals when rippin' it:



Solder a .68uF or 1uF polyester capacitor in parallel with R97, i.e. just solder it next to it/over it.
Like so. I used some hot glue to secure it with a few dabs to caps nearby, and shrink wrap on the wires.

Next up, let's fix that insane negative feedback amount:


Replace R58 with a suitable resistor. JVMForum gives these guidelines on what values to use for what effect:

R58 = 47k -- late '60s Plexi
R58 = 74k -- early '70s MkII Plexi
R58 = 82k -- stock JVM
R58 = 137k -- EVH's Plexi
R58 = 176k -- JCM800 2203
R58 = 177k+ -- a Marshall with almost a Vox's lack of headroom in the power amp

I myself went for 180k because I love me Marshalls with no neg feedback, untamed :-) (My Ceria also had a switch to make it have pretty much no feedback and I liked it that way).

Now when those are done, remove the R106 resistor and solder the lines from the choke there instead. Best do it last, because likely the choke leads aren't hugely long. And I hope you put the choke somewhere close :-)



Like that. Here you also see the resistors between the caps that you can measure from if the caps are drained.

That's it!

I screwed up my before/after clips, but here's some going thru sounds after. Recorded with a (NB): single-EMG85 equipped superstrat/metal axe...so the cleans aren't exactly clean and the bridge pickup only of course is what it is. But who needs neck pups with an EMG85 :-)

I REALLY REALLY REALLY can't tell you how much I love the changes.

Immediately it was apparent the amp was a bit louder and touch more gainier, so I had to lower my channel volumes just a touch, and some gain too. But MAN it sounds so much better.

The clean channel is now just like a Bluesbreaker. You hit chords, they just BRAMMM out there with utmost Vox-like clarity and punch, and there's WAY more pant-flapping lower sound content. Kinda like someone put in bigger speakers. That's mostly the lack of negative feedback I guess.

The 2nd clean is instant pure old ACDC. Just like a hotrod Plexi. Warm and big, too.

Drive 1 is now exactly Iron Maiden on The Number of The Beast etc...and perfect for any rockin'. JCM800 at its best.

Drive 2 is now way more loose and usable, growls almost like a Mesa or something, and screams in solos. Nicely there's now even a touch of slight sloppiness and growl where there used to be tight upper-middy bite. And even the craziest bends don't grate on ears now, even without picking and just hammerons it's instant Gary Moore and sustain 4 ever.

Here's some sloppy playing after the mods, going from cleaner towards the hotter channels.

http://deeaa.pp.fi/clips/JVM_MODDED.mp3

Hello. I'm new on this forum. I registered because of the info about jvm's.it's great to have the oportunity to communicate with you all. Well, I have a jvm210h and I already bought an MM 3h choke that I haven't install yet. I want to know how to do the other mods mentioned on this discussion on the 210h since the components inside are not necessarily identified with the same name (r58, r67, etc.), and maybe to get same results there is a different way. I'll apreciate any help. Thanks.

[deeaa*]

Do check out jvmforum.com, there should be lots of info there...surely on the 210H as well!

[Ramo]

Do check out jvmforum.com, there should be lots of info there...surely on the 210H as well!

Opened the jvm210h today to put an MM 3h choke. Noticed that the main board looks the same as the 410. R58 was there and was 82k. I put a 150k. Put a .68 micro f cap with R97. Wooooooooooow! The distortion is transformed. More clarity, definition, articulation. There is more sparkle on the clean green. Way better. Thanks.

[deeaa*]

Excellent! :-)

[Ramo]

Excellent! :-)

Have you done the c83 mod? I didn't find it on the board. Do you know where is it? Is it on the controls board? Thanks.

[deeaa*]

Have you done the c83 mod? I didn't find it on the board. Do you know where is it? Is it on the controls board? Thanks.

Nope it didn't seem like a mod I'd like...that should lessen highs some and lower red od channel gains...I like it as it is now. A Marshall should be a bit on the bright side and cut thru the mix IMO.