JCM 800 Mods - Need Advice, Recommendations

Jeff_H · Apr 13, 2004

Ok - here's the deal. My JCM 800 4212 (2205 circut) is due for a recap I believe. It's really noisy on both channels....I've tried switching, changing pre-amp tubes to no avail. The power tubes have less than 40 hours on them, so that should not be an issue. I thought while I had it on the bench I would have some mods done to it. I've seen several of you here talking about mods you've done yourself that are fairly simple. I do not have enough electronics knowledge or experience to attempt any mods myself.

There are several people out there (Trace at Voodo, Jeff Seal, Dave Bray) that mod the 2 channel amps to give a really good clean channel and smoother overdrive that is available at lower volumes. I'm trying hard to justify spending $400 + shipping both ways on an amp I payed $500 for. I don't play professionally, and I don't play out right now, so this is for pure personal enjoyment.

What have some of you done, and what have been the results? Did you get a better clean channel? I don't really need more gain, just smoother more liquid gain. Anyone out there have suggestions on whom I could send it to that may not be as expensive? Anyone on the board do these mods? Some of the schematics make it seem like the mods are not a big deal, but I just don't want to screw my amp up trying myself.

Thanks in advance.

Lee_M. · Apr 13, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

Jeff,

Give my friend, Scott Splawn, a call at 704-922-0020. He is a super guy that has a small shop near Charlotte. He is a killer picker and does great work on Marshalls. I've done a good bit of business with him. He is very honest and very knowledgeable. Check out his website, below.

http://www.splawnguitars.com/

Best,
Lee Moore

Reckless Abandon · Apr 13, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

I had a dual stage maste rput in my 800. It gave me tons more gain and more fullness. So now I turn the gain to 1 1/2 -2 and my master up. I do not use all of the gain it just allows me to get more power tube in there. 80's metal machine now. I go the mod from torres. I know this is not what you mentioned you wanted but this is what I got.

Jeff Seal · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

I'd be more than happy to help you, but I really don't remember exactly which circuit your amp had (old or new) ..sorry, I talk with a lot of people and don't remember who has what...

If you're unsure, I can tell you how to determine which one it is.

We'll proceed from there....info is free...just tell me what you're after very specifically.

Jeff Seal

Jeff_H · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

Jeff -

You're actually the first person I think of when considering getting my amp modded. I'm just not sure I can justify the top $$ mod for my use...but I want it!

You told me once to pull V2 (I think) to see which version I had. I saved the info you gave me on the old board, but it got wiped. What I really want from the amp is a more useable clean tone. Fender cleans would be optimal....I understand you can get close. For the OD I just want it to be a tad smoother, slightly less grainy. I don't know that I need a ton more gain, because when I have it dimed it's more than enough. Just smoother, slightly more liquid but still "Marshally", and a more useable sweep with the gain knob. I don't really notice much difference in gain between say 2 and 7 on the dial, more of a volume change. Between 7-10 is where I get noticable gain differences. Having a more saturated gain sound at lower volume levels would be a great plus as well.

Also, there seems to be an overall level balance issue between the clean channel and the OD, with the clean channel being significantly louder. All of the tubes have been recently replaces, including some great NOS pre-amp tubes (RTF and Jan/GE).

Artists who's tone I like:

SRV for clean and dirty blues tones
Slash
Gary Moore
Great White (don't laugh, great driving rock tone IMO)
STP

If you let me know which tube to pull again I can let you know right away which version I have. I want to say the newer, but can't be sure. Also, I think the caps need to be replaced.

Thanks as always.....Jeff

Jeff Seal · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

No Problem.... pull V2 and either the clean channel will quit working or the OD channel will quit working. (you're not gonna hurt the amp, I promise...but do turn it off before doing this)

If the OD (Boost) channel quits working , then it's the early version.
If the Clean (Normal) channel quits working , then it's the later version.

In either case, the other channel should function....

Just a quick note.... I'll give you the mods for free...and your Marshall can nail the exact tones you described, but we may have to push the limits of your personal technical abilities.... but basically if you can solder...we're there!

My Clean mods are exact (not bragging..) and I mean exact Fender clean's and I'll give anyone $100 who can tell the difference between my 2210 and my or any other properly working Fender Twin...but be advised it is a radical change from what you're used to.

I'll await your findings.....

Jeff Seal

Jeff_H · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

Pulling V2 kills the clean channel...so I have the later version.

It's very kind of you to offer the spec's on your mods for free.....but I am barely competant to solder in pickups...I'd never make it working on an amp. Besides, I'd rather pull the chassis and ship it to you to make sure it's done right. Being a hobbiest, I'm just trying to decide if $400-$500 worth of mods + shipping is practial for me.

I have no doubt everything you do it top notch...Scott_F said after the Texas Jam that your Marshall had the best cleans he'd ever heard from a Marshall. I've looked on the net, been to almost every person's web site who offers mods, and by far you have been the most helpful and kind. I've also read many of your posts at the Marshall forum.

If you would rather PM me with specific details and approximate cost...no problem. I understand that everything is approximate untill you actually see the amp. It's almost 20 yrs old, and has probably never had a proper run thru.

Thanks again....Jeff

Jeff Seal · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

Let me see what I can figure out to best help you and I'll PM you

Jeff Seal

mrid · Apr 14, 2004

Re: JCM 800 Mods - Need Advice, Recommendations

I did these mods to mine http://www.tone-lizard.com/Ultimate_JCM800.htm

darkshadow54321 · Apr 14, 2004