want to mod JCM800 (2210), more gain needed

[wizard333]

There are a lot of things you can do to these amps. I have a very extensive set of mods that is very different from what is posted here.

However, the biggest thing you can do to "increase gain" is not a mod. Look at the schematic. Channel "volume" for the OD channel isn't where "volume" should be, it's really a gain knob. Dime that, dime the gain, control overall volume with the master. It has a truck load of usable gain just by doing that.

Beyond that the rabbit hole goes deep. I always liked the OD channel but hated the clean channel, so I put a Fender clean channel in mine. This is MAJOR SURGERY and not for the weak of heart. This completely separates the channels, I no longer use V1A for cleans, just V2A/B. A by-product is that the gain on the gain channel goes way up since the clean channel isn't sucking huge amounts of signal after V1A. That alone gives the gain channel more gain than you can use. Dime the gain knob even without channel volume high and the guitar will just uncontrollably feedback at anything above conversational volume, its way too much gain to put to actual use at the top of the dial. Channel cross-talk is gone. This amp will do Fender style cleans better than a lot of Fenders with the right changes. I also disconnected the clean channel from the MV.

Past that, there are many things to be changed on the gain channel if you want, but it really comes down to taste at that point, there isn't a thing wrong with the gain channel as it sits.

[wizard333]

Just for grins I removed all the diode clipping junk from the gain channel. The gain definitely goes down, although with gain and channel volume dimed and MV rolled back to reasonable levels, the upper levels of gain are still quite healthy after the clean and gain channels were separated. With the diodes in there, the upper levels of gain were just feedback even at low volumes with the channels separated. Way over the top.

The BIG ADVANTAGE is that the amp is now much more touch sensitive and responsive at lower gain levels, where it sort of felt thuddy and resistive to pick attack at lower gain levels with the clipping diodes/bridge rectifier in there. I didn't add a Ck to V1B. That could be used to boost upper gain levels back into the stratosphere, but frankly I just don't play with that kind of gain anymore and its easier for me to dial in nice lower gain sounds without that in there. If you wanted over the top gain back without the solid state clipping in there though, it would be easy enough to dial it (way) back up. 470k Rp/10K Rk is a very high gain stage when bypassed, and no wimp when not bypassed.

PS: A lot of the suggested "mods" in this thread don't do what the OP requested, i.e. more "gain". Some of them are completely unrelated to that purpose, at least on the gain channel, and some of them are at cross-purposes. Take them with a grain of salt.

[wizard333]

This thread got me thinking about that amp again so I messed around with adding a CK to the second stage and slightly tweaking a few other values.

For one thing, you can get a BONE CRUSHING amount of usable gain from 3 tube stages, which I think I've mentioned before elsewhere on this forum. Why Marshall decided to use clipping diodes is a mystery because without them I can get even more gain from the same 3 stages. Not only is the amount of gain at the top end of the spectrum more, but the amp responds and sounds great at anything from very slight overdrive all the way up to insane gain and everything in between, which it definitely did not do with the diode clipping in there. The diode clipping made the amp sound and respond rather fizzy and dull at anything below high gain.

It seems like 4 and 5 stage gain channels are all the rage and have been for a while, but they aren't really necessary for producing as much usable and good sounding gain as you can get. There is a limit on usable gain; at the point where your guitar is just feeding back uncontrollably even at moderate volume, you've passed that point. 3 stages is enough to take you right to that wall.

[jmaf]

Just for grins I removed all the diode clipping junk from the gain channel. The gain definitely goes down, although with gain and channel volume dimed and MV rolled back to reasonable levels, the upper levels of gain are still quite healthy

I think you're using distortion and gain interchangeably? The gain doesn't go down from removing clipping diodes, the distortion does. As you noted, one problem with diodes is you lose touch sensitivity. Once you install clipping diodes on one of the first gain stages, your guitar's volume control only becomes effective from 1 to 2, then from 2 to 10 your guitar will be distorted nearly by the same amount. And it doesn't really matter how much gain you add after that, you'll only get closer and closer to a square wave.

470k Rp/10K Rk is a very high gain stage when bypassed, and no wimp when not bypassed.

Rule of thumb, divide one by the other. With that pair you'll get 47x gain(~33dB). You can get closer to 60x(36 dB) by using the traditional 100K Rp/1.5K Rk. Assuming a 12ax7 of course.

[Gtr_tech]

This thread got me thinking about that amp again so I messed around with adding a CK to the second stage and slightly tweaking a few other values.

For one thing, you can get a BONE CRUSHING amount of usable gain from 3 tube stages, which I think I've mentioned before elsewhere on this forum. Why Marshall decided to use clipping diodes is a mystery because without them I can get even more gain from the same 3 stages. Not only is the amount of gain at the top end of the spectrum more, but the amp responds and sounds great at anything from very slight overdrive all the way up to insane gain and everything in between, which it definitely did not do with the diode clipping in there. The diode clipping made the amp sound and respond rather fizzy and dull at anything below high gain.

It seems like 4 and 5 stage gain channels are all the rage and have been for a while, but they aren't really necessary for producing as much usable and good sounding gain as you can get. There is a limit on usable gain; at the point where your guitar is just feeding back uncontrollably even at moderate volume, you've passed that point. 3 stages is enough to take you right to that wall.

We share the same philosophy then. I think a 3 stage pre is really the way to go if you want to retain the sound of the instrument and have some available dynamics. Anything more than that and its just undefined mush.....and noise. Even a 3 stage setup can be mushy if not properly designed. Its all about *not* running each stage flat out in order to get waveshaping evenly across the 3 stages instead of any single stage driving the next one into submission. I tend to keep my coupling cap values a little on the low side to roll off low end trash I don't want screwing with the gain stages. Smooths it out.

Try a .001u cap across (not to gnd, but across the in/out terminals) yer guitar vol pot. It keeps the loading mud from happening and basically turns it into a remote preamp gain control. You'll get usable tones across pretty much the entire range.

[olddawg]

This has been a very interesting thread. But I do know that when you go to buy one of these amps everyone wants a clean, unmodded, unmolested amp. IMHO you will never make one into a Triple Rectifier Mesa if you want that kind of gain. I have found that a Proco Rat and an decent overdrive (like a Bad Monkey) work very well with these amps. I played an outdoor gig a couple of weeks ago with a provided backline of two stock JCM 800 (series II with reverb) halfstacks and a JCM 900 halfstack. Everything was fine with my pedal board. ( I also use a compressor) IMHO, if you really want more gain, sell the amp and get a Mesa or Laney or a 5150 or something rather than endlessly modding a decent amp. People added gain stages to JCMs 30 years ago because there were no high gain amp options available at that time. There are alternatives now. My two cents anyway.

[wizard333]

I think you're using distortion and gain interchangeably?

Yes the colloquial meaning. Would you like me to be more technical? You knew what I was talking about right?

The gain doesn't go down from removing clipping diodes, the distortion does.

Feel better now?

As you noted, one problem with diodes is you lose touch sensitivity. Once you install clipping diodes on one of the first gain stages, your guitar's volume control only becomes effective from 1 to 2, then from 2 to 10 your guitar will be distorted nearly by the same amount.

Not really, the volume control is still effective, albeit less so. The overall sound/feel just isn't as pleasing.

IMHO you will never make one into a Triple Rectifier Mesa if you want that kind of gain.

It does that kind of gain. Past a certain point, gain becomes uncontrollable feedback. I purposely dialed the gain back to the point where, with channel volume (really another gain control) and gain dimed, it was just below the uncontrollable feedback point. I could easily push it well past that point, but well, why?

People added gain stages to JCMs 30 years ago because there were no high gain amp options available at that time. There are alternatives now.

These were contemporary with high gain Mesa amps, maybe you aren't old enough to remember. Mesa Marks had crazy amounts of gain in the 80s. These Marshalls also had quite a bit of gain on tap stock. Listen to Michael Schenker or Tom Morello, no fuzz box there. Don't confuse a 2210 with a 2203, not at all the same animal. "JCM800" Doesn't mean only 2203/2204. "Chevy" doesn't mean just Camaro. I personally do not care for the 2203/2204 and never have. Thin, squaky and wimpy on the drive unless you crank them way up. Even stock I much prefer the 2210/2205/4210/4212 variant, and modded it's just lightyears past a 2203/4.

FWIW, tonally, versatility, and touch wise, this mod kicks the living holy hell out of a Triple Rec, Laney, 5150, etc. Both the clean channel and the gain channel smoke those hard, and it has tube driven spring reverb. Mine also has footswitchable solo/clean boost across both channels which I added in 1992, before Mesa was doing it. The problem with most high gain amps is the tone and feel is just awful. It's easy to build an amp with a lot of gain, its another thing entirely to have it sound like something other than mud mixed with angry mosquitos, or not to feel thuddy unless the gain is cranked way up. 5150s, Rectifiers don't do low gain well. All the haphazzard high end dumping leaves them feeling stiff and resistant to pick attack at lower gain levels; 5150s don't do much except scooped and buzzy in any case, Rectifiers are muddy on chords if higher single notes sound good, buzzy and thin on high notes if chords are defined. Not much room in between. The old high gain Laney's try to run too much low end through the gain stages and end up with farty low notes.

The point of this experiment for me is to take the stock amp, where the clean channel was meh and the OD channel quite passable, and add a Fender clean channel with more versatility, dial the gain channel so it does everything from mild OD to very high gain and anything in between and sound/feel good doing it, and retain the tonal versatility these amps have to do everything from blues to high-mids medium-gain classic rock and scooped out metal. Frankly, there AREN'T many alternatives out there that can do those things at all, in fact none leap to mind in a stock commercial amp.

With that pair you'll get 47x gain(~33dB). You can get closer to 60x(36 dB) by using the traditional 100K Rp/1.5K Rk.

Unbypassed 470/10k is 30 ish, 100/1.5 is 30 ish. The 60 ish you are talking about is FULLY BYPASSED gain, but if you bypass the 470/10k you get 87, not 30. Compare apples to apples if you are going to compare. Also, 470k Rp/10k Rk is not center biased like 100k Rp/1.5k Rk, it has a different sound and feel to it, and clips differently, regardless of gain. Again, if you're going to compare, compare apples to apples.

Try a .001u cap across (not to gnd, but across the in/out terminals) yer guitar vol pot. It keeps the loading mud from happening and basically turns it into a remote preamp gain control. You'll get usable tones across pretty much the entire range.

Check this out: GuitarNutz 2 - A better treble bleed circuit

[jmaf]

Empty your glass first if you wish to get served. If I knew you knew everything, I wouldn't have even tried.

[Joe L]

Empty your glass first if you wish to get served. If I knew you knew everything, I wouldn't have even tried.

Wow, what a thread ender!

Just to revive, errr... beat a dead horse if you will.

The aformentioned amp is not to my taste. I ordered a 4212 combo in '86 sight unheard and received something other than what I expected a Marshall to sound like. The best thing I can say about it was it was the reason that I built my Mesa Mark III clone shortly afterwards.

In '99, I figured what's to lose and gutted the amp. I tried a few circuits until I settle on the 2550 Silver Jubilee a couple of years ago. I had two extra preamp sockets so I paralleled the first stage. Very cool! Some extra gain without extra noise and I still had an extra socket. Even the transformer part numbers matched between models so this was a very cool mod. The 2550 uses some very cheap ceramic caps all over the amp so its very easy to spend a few bucks more on film caps on a rebuild. Even though the amp uses LEDs for clipping, the filtering is very good and the tone stack is killer! The clean channel clip circuit is useless so don't sweat implementing it if you don't have the parts. The clean channel is very useable if you can find a compromise between lead and clean settings. Of course, since you are rebuilding the amp, you can add your on "seasoning to taste".

So here is my killer mod for a 2210/4212:
Build a Ceriatone 2550 on the Lead channel side controls. That only takes up 3 preamp sockets so use V2b in parallel with V3a for a hotter input stage with appropriate values. Use V1 for an EF86 stage on the clean channel controls. You can either use it with only a volume control direct into the PI or do something with V2A to drive the clean channel tone controls.

[wizard333]

Sounds like what you got was the original version of the 4212, the one with the pre-gain tone controls. The later version and the Jubilee shared the same tone and response, but the non-Jubilee had more gain on tap. If you look at the latter version schematic vs. the Jubilee, the Jubilee is actually sort of a dumbed down version of the 2205/2210/4210/4212.

[Joe L]

Sounds like what you got was the original version of the 4212, the one with the pre-gain tone controls.

Nope. It was the later version, bought it in '86. Has the IC for switching and the bridge for clipping.

It is a matter of taste I guess because I've seen live vids of pro bands using that model in Lead mode. They sounded just like mine and were equally as bad.

I wanted the combo because I got tired of lugging my half-stack '77 2203 around. That amp still sounds great.

[wizard333]

How were you setting the knobs? I can't wrap my head around that one.

[olddawg]

Hey Chris,

I'll just write in English since this is an English forum. But I'm Dutch as well. I've heard of CMW Amps before, through Voodoo amps actually, it seems like you know your stuff . I've been looking for mods for my 2205 for a while and couldn't really find them, unlike mods for the single channel 800's. Couldn't find anyone here in the Netherlands that actually knew how to improve or mod 2205/2210's. Someone from Dr. Tube actually said they don't do these amps cause they don't know mods for those, the reason was they use diode clippers and so the circuit wasn't interesting enough. Thought it was a strange response but okay. They also said these amps were too rare in the Netherlands to actually develop mods for them.

I was just wondering. Do you maybe know some easier and cheaper mods that work very well? I've already done some, only with replacing resistors with other values or shorting or clipping out resistors or caps. Or adding caps etc. It improved it quite a bit. Though I'm curious if it makes such a difference if I replace or short out those caps I can't reach cause they're too close to the PCB; I have to flip the PCB over and that's a bitch cause the pots with the control knobs are fixed to the PCB. And I have to take those out in order to get underneath the PCB.

Unfortunately I'm not really looking for the more expensive things like OT replacements or a complete overhaul by a good amptech like you. I'm very sure it's worth it though.

Chris, do you know if it can do these type of tones eventually?:
http://www.youtube.com/watch?v=UdSdgOYBH88

Any help for a Doe het zelver?

If you want "easy and cheap" for more gain and more balls have you simply considered putting a Bad Monkey OD or a Proco Rat (or something like them) or both on the input? Even a compressor like the Rocktron. You might be surprised. Sometimes the simplest solution is the best. Not everything needs to be modded.

[hotguit]

Hi
I know it is a very old thread but it is very interesting
As i'm going to mod my jcm 800 2210 ('86) my question is:
switching green wires as in HTH schem is the free triode ready to work or it needs to be rewired for working as added gain stage?
I mean, i had ONLY to switch the green wires and i am done? or what?
thank you
hotguit

[wizard333]

You're looking at the wrong animal. There is no "free triode" in a 2210. The only way to create one would be to "steal" the effects loop recovery stage.