want to mod JCM800 (2210), more gain needed

[sgw2210]

2210 Mods

This is a great thread! I just got a 1982 2210 last night from ebay. It's great and it was just overhauled with new caps. It sounds amazing but I want to make it "personal" if you know what I mean. Honestly I'm just getting into modding. I've taken some electronic engineering classes in college and am looking to apply the stuff I've learned.

HTH, post up what you end up doing. I'm looking forward to it!

Stefan

[HTH]

The 2210 is sounding really nice, but I would say there is still some work to be done...

R4 (100k plate resistor) to 220k for more gain. I like this one, more gain for sure – it’s a keeper.

R3 (10k) to 2k7, also remove D1 bypassing cathode and use 0.68uF cap to bypass R3. removing D1 lowers gain quite a bit, but overdrive ‘feels’ more valve-like and natural/organic, it does however take some sizzle from the tone and need to re-EQ amp to compensate for treble loss (though a cathode bypass cap would most likely take care of that). Lowering cathode resistor (R3) to 2k2 increased gain, but not a mental amount like expected. Have added 0.68uF cap across cathode resistor, added more gain and snarl in hi-mids. The diode and 10k still had more more overall gain, though the tone was more ‘transistory’.

R14 (150k plate resistor), change to 100k – this affects just the clean channel, – gives more clean headroom, can now have clean channel gain on 4 or 5 instead of 3. Could use a split-load plate resistor for less gain.

R21 (470k), this is the ‘mixer resistor’ for the clean channel to connect it to the ‘input’ of the reverb stage. Could increase this resistor to 1M or even 2M2 for less gain and cleaner cleans. HAVE YET TO TRY THIS BUT SHOULD WORK FINE.

R25 (1k5 cathode resistor, reverb recovery stage), 22uF cap across cathode for more gain. Tried this and the amp is quite a bit more gainier and MUCH fuller bass end. Also tried a 0.68uF cap which added more crunch in the hi-mids/treble. The 22uF sounded better, but possibly had a little bit too much bass, 10uF was better and 5uF would probably be 'just right'.

R41 (330k in PI), change to 1M. R44 (120k in PI), change to 1M.
R43 (470ohms in PI), change to 820ohms. Made amp sound ‘classic Marshall’ and removed ‘plasticy/fake’ tone from amp.

C32 and C34 (0.022uF), change to 0.047uF for more bass chunk.

Finally, my fave mod for this amp... remove the NFB. The amp has more gain and is louder/more ‘open’ sounding. Also change 22k in PI to 47k.

6550s instead of EL34s also sound much better (just tweak the bias supply for more bias voltage)

[HTH]

ADDING A GAIN STAGE (from the clean channel to the boost channel)...

I've been looking at the 2210 a bit more and it makes no sense to have three gain stages for the clean channel and the same amount for the boost channel.

Is this so that the signals are in phase with each-other when mixed at the reverb stage?

Since I want less gain on the clean channel and more gain from the boost channel, it makes sense to take a gain stage from the clean channel and use it for the boost channel. This will mean that the clean channel goes through two gain stages and the boost channel through four and will still be in phase with each-other, right?

I'm planning on putting the 'extra' gain stage between VR4 and VR5 on the boost channel with appropriate voltage dividers applied where necessary.

Anyone forsee problems with this idea?

[sgw2210]

Finally, my fave mod for this amp... remove the NFB. The amp has more gain and is louder/more ‘open’ sounding. Also change 22k in PI to 47k.

I'm looking forward to getting into those mods. I just gotta find someone who can show how to discharge the caps.

Seeing as I'm new to this, what's an NFB and how do I take it out?

[Robert M. Martinelli]

Since I want less gain on the clean channel and more gain from the boost channel, it makes sense to take a gain stage from the clean channel and use it for the boost channel. This will mean that the clean channel goes through two gain stages and the boost channel through four and will still be in phase with each-other, right?

I'm planning on putting the 'extra' gain stage between VR4 and VR5 on the boost channel with appropriate voltage dividers applied where necessary.

Anyone forsee problems with this idea?

Hi HTH,
With all these mods your 800 is starting to look like a spaceship....let us know when the liftoff is due

Ok, seriously, only problems I can think of are some crosstalk issues between the channels ( 'couse half of a preamp tube will belong to the clean channel and the other half to the boost channel ) and possibly some oscillation problems, since you removed the NFB and you're planning to add an extra gain stage.

Let us know how you end up with the mods, chances are I will break my own rules and buy a JCM800 to play with instead of getting myself another Vox amp!

Best of luck!

Bob

[Robert M. Martinelli]

I'm looking forward to getting into those mods. I just gotta find someone who can show how to discharge the caps.

Seeing as I'm new to this, what's an NFB and how do I take it out?

Hi sgw2210,
NFB stands for Negative FeedBack ( loop ) - it means some of the signal is fed back ( out of phase ) to a previous stage, gaining stability at the cost of lesser gain.

Hope this helps
Best regards
Bob

[HTH]

Hi HTH,
With all these mods your 800 is starting to look like a spaceship....let us know when the liftoff is due

Ok, seriously, only problems I can think of are some crosstalk issues between the channels ( 'couse half of a preamp tube will belong to the clean channel and the other half to the boost channel ) and possibly some oscillation problems, since you removed the NFB and you're planning to add an extra gain stage.

Let us know how you end up with the mods, chances are I will break my own rules and buy a JCM800 to play with instead of getting myself another Vox amp!

Best of luck!

Bob

when I first looked at the schematic of this amp I was looking for 'tweaks' in the same way as you would with a single channel JCM800 (2203/2204), but the 2210 doesn't really have much scope for that imo (if you really want the best out of it). You have to dig a bit deeper with this one, do some rewiring - changing a resistor or adding a bypass cap ain't gonna transform this puppy.

The clean channel is much better if you remove the stage with the 10k cathode resistor (V2a) and instead go straight from the clean channel volume's wiper into V2b's grid. This is really easy to do as well - just unsolder V2b's green grid wire (tape it up), unsolder V2a's green grid wire and resolder it to V2b's grid. You get a much better clean tone and the bleed-thru on the gain channel is improved.

I reckon the clean channel tonestack can be rewired (with a bit extra effort) to BF Fender specs and that should REALLY nail the clean tone. Having PCB-mounted pots really limits what can be done while making a clean job of it.

The OD channel is better with the clipping diode stuff taken out and revoiced where appropriate/to taste.

The NFB 'might' stay disconnected, really depends on how the extra gain stage works out.

[BeëlzeM]

Sorry to bump this up, but I have some questions on this matter as well. With my 2205, which has practically the same schematic.

I was looking for more gain as well, to get more of a Slayer/Sepultura kinda raw deep tone. Don't care for my cleanchannel much.

Here's what I already did:

- 10 kOhm resistor across R13 on V2(10 kOhm) for quite a bit more gain.
- Replaced R16 on V2 with a lower value for a bit more response and a slight gain increase.

I have been looking in another thread I made for other types of diodes and diode bridges (D6 and W005). Not sure what to do here...

I already came across some interesting mods in this thread:
- R4 (100k plate resistor) to 220k for more gain.
- R25 (1k5 cathode resistor, reverb recovery stage), 5uF or 10uF cap across it.
-C32 and C34 (0.022uF), change to 0.047uF for more bass chunk.
- remove the NFB. The amp has more gain and is louder/more ‘open’ sounding. Also change 22k in PI to 47k

Any way someone can clear that up? I have no actual experience with the Negative FeedBack loop.

What are some mods you would really recommend, keeping in mind what kinda tone I'm after?:
http://www.youtube.com/watch?v=fD0PJ-fKeHA
http://www.youtube.com/watch?v=F8kQ3MKMeDc

Thanks

[HTH]

Sorry to bump this up, but I have some questions on this matter as well. With my 2205, which has practically the same schematic.

I was looking for more gain as well, to get more of a Slayer/Sepultura kinda raw deep tone. Don't care for my cleanchannel much.

Here's what I already did:

- 10 kOhm resistor across R13 on V2(10 kOhm) for quite a bit more gain.
- Replaced R16 on V2 with a lower value for a bit more response and a slight gain increase.

I have been looking in another thread I made for other types of diodes and diode bridges (D6 and W005). Not sure what to do here...

I already came across some interesting mods in this thread:
- R4 (100k plate resistor) to 220k for more gain.
- R25 (1k5 cathode resistor, reverb recovery stage), 5uF or 10uF cap across it.
-C32 and C34 (0.022uF), change to 0.047uF for more bass chunk.
- remove the NFB. The amp has more gain and is louder/more ‘open’ sounding. Also change 22k in PI to 47k

Any way someone can clear that up? I have no actual experience with the Negative FeedBack loop.

What are some mods you would really recommend, keeping in mind what kinda tone I'm after?:
http://www.youtube.com/watch?v=fD0PJ-fKeHA
http://www.youtube.com/watch?v=F8kQ3MKMeDc

Thanks

ok, in the end I completely rewired most of the amp and now it has a Fender Twin clean channel and a SLO100 overdrive channel - WAY too much to describe here.

if you're after 'tweaks' using the existing topology, here's what I found to be the best...

OVERDRIVE CHANNEL MODS
* short C1 (0.047uF) with a wire
* R4 (100k) to 220k
* clip out R12 (220k)
* short out C39 (0.047uF) with a wire
* clip out C20 (0.002uF)
* bypass R25 (1K5) with a 10uF cap
* clip R46 (1k5), this will disable to DI function, but I found this improves the tone AND allows you to use a cap in the NFB loop to beef up the bass end.
* add a 4700pF cap between the purple NFB wire and the 8ohm tap on the impedance selector.
* R43 (470R) to 820R
* R41 (330k) and R44 (120k) to 1M
* C32 (0.022uF) and C34 (0.022uF) to 0.047uF
* R47 (100k) to 47k

CLEAN CHANNEL MODS
* unsolder the green grid wire going to the clean channel's volume pot and resolder it to the other grid on the same tube (V2b). Of course you'll have to unsolder V2b's existing green grid wire and tape it off. This free's up a gain stage for use with the overdrive channel if so desired.
* clip out R19 (100k)
* clip out C15 (470pF)
* short out R18 (150k) with a wire
* bypass R16 (1k5) with a 22uF cap

the diode clipping (W005 and D1) really stifles the amp's tone - taking these out really opens the amp up, but removes some gain. However, you have the gain stage (V2a) to play with as you're not using it for the clean channel anymore.

[BeëlzeM]

Hey man, thanks for the quick reply. Those value changes are pretty easy to do and I will definately try them out. With 'clip out' you mean just taking it out and wire it as if there was nothing, right? And with 'short out' just placing a short wire across it, correct? English is not my native language so I don't get english technical terms right away .

How would wiring that gain stage work? The one for the clean channel. I have to unsolder the green wire going to the clean channel's volume pot and where should I solder it to on V2? Unsolder the existing green V2 wire and tape it off? So I can use that wire for another gain stage. How do I go around doing that?

Any way you could clear this up a bit maybe?:

* clip R46 (1k5), this will disable to DI function, but I found this improves the tone AND allows you to use a cap in the NFB loop to beef up the bass end.
* add a 4700pF cap between the purple NFB wire and the 8ohm tap on the impedance selector.

I have no experience with the NFB and how that works whatsoever.

Overall, what did all those easy to do mods in the first list do? How did it alter your tone and how much? Did you like it? How were it's characteristics? What did improve and which mods did what?

Thanks in advance man...

[HTH]

you got it, when I say 'clip out' I mean literally remove the component either by desoldering or with some side-nose clippers.

when I say 'short out' I mean to solder a wire across that component which is the same as unsoldering it and replacing with a piece of wire. you choose which-ever is easiest.

for the clean channel mod where you remove V2a (the stage with a 10k cathode), look at the schematic - all you are doing is taking the wire that goes from the clean volume pot to V2a's grid and instead wiring it to V2b's grid. the existing green wire that goes to V2b's grid is just taped up.

as for the mods listed, I'd do them all together - trust me, it WILL sound better than stock.

[BeëlzeM]

Heheh, so 'Clip out' is removing the component and replacing it with nothing. Just removing it all? As if there was nothing?

'Short out' is still with the component there but a wire soldered to + and - right over the part? Sorry for asking again

About the other mod. I don't get that for the most part. The green wire that goes from the clean channel pot to the V2a's grid should be wired to V2b's grid and the one that goes to the V2b's grid stock should be taped up. I get that. Any number from the schematic you can give me?

What could I do with that gain stage that came free? I get it right it actually came free right? Can I use that with the boost channel? How should I wire that? An extra gain stage on the boost channel seems nice...

What about the NFB? What should I do with that? Any chance to clear that up just a bit?

I will definately try them all. Just wanting to know if this would get me closer to the tone I'm after... the Slayer/Sepultura kind of tone. Heavy, nice and tight bass and midrange growl. But I'm sure it will.

[HTH]

Heheh, so 'Clip out' is removing the component and replacing it with nothing. Just removing it all? As if there was nothing?

correct

'Short out' is still with the component there but a wire soldered to + and - right over the part? Sorry for asking again

you got it.

About the other mod. I don't get that for the most part. The green wire that goes from the clean channel pot to the V2a's grid should be wired to V2b's grid and the one that goes to the V2b's grid stock should be taped up. I get that. Any number from the schematic you can give me?

you got that one too. look at the schematic, it'll all become clear. the junction at the clean channel gain pot's wiper and C4 (100pf) connects to V2a's grid via a green wire (this is pin2 on V2). the junction of C13 (0.022uF)and R15 (470k) connects to V2b's grid (pin7) via another green wire. you need to disconnect the green wire that goes to pin7 on V2 and tape it up (this is your 'free' gain stage that you can use for the boost channel if desired). unsolder the green grid wire that connects to pin2 on V2 and resolder it to pin7 on V2. This will give you a cleaner clean tone and not the crunchy Marshall 'clean' tone.

What could I do with that gain stage that came free? I get it right it actually came free right? Can I use that with the boost channel? How should I wire that? An extra gain stage on the boost channel seems nice...

you can use it with the boost channel, but you'll have to revoice the boost channel alot.

What about the NFB? What should I do with that? Any chance to clear that up just a bit?

not sure what you mean, the NFB is connected up to keep the amp tight in the bass end (flattens the frequency response). this is at the expense of some gain, but not that much really. if you want to get a chunkier bass end, unsolder the purple wire that goes to the impedance selector and connect a 4700pF cap between the free end of the purple wire and the point on the impedance selector where you just unsoldered it from. you will want to clip out R46 (1k5) otherwise this doesn't really work. you will have that BIG fat bass end you like on the Sepulture records (like on Choas AD or Roots)

I will definately try them all. Just wanting to know if this would get me closer to the tone I'm after... the Slayer/Sepultura kind of tone. Heavy, nice and tight bass and midrange growl. But I'm sure it will.

yep, try them all - there isn't really a 'tweak' with this amp (imo), it needs lots of work to get it sounding REALLY nice. in the future, I'd just buy a single channel JCM800 (2203/2204) and a Boss SD-1 for more gain - it's a much better tone than the 2210 (unless you heavily mod the 2210 like I have).

[BeëlzeM]

Thanks for explaining man. I got myself some components for the easier mods. I'm leaving the clean channel mod, the one with the green wires to V2a and V2b, alone for now. Since I'm not using the clean channel that much, was only interested if using that gain stage for the boost channel would work out fairly easily. I assume you didn't try that one out? Sounds like that revoicing of the boost channel with the fourth gain stage added takes a lot more. Might also try the impendance selector mod, that sounds easy as well.

Anyway, this amp can sound REALLY nice, right, with those things done? Can it compete with the single channels afterwards, for the heavier metal tones?

[BeëlzeM]

In addition to my post above.

How did you manage to short out C1, C39, and replace C32 and C34? They're as close to the PCB as they can get. Do I need to get underneath it?