JCM 800 2204 - Help me figure out the mods

Discussion in 'Marshall Amps' started by T0rch, Feb 28, 2020.

  1. T0rch

    T0rch New Member

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    So I’ve had this JCM 800 2204 for about a year now. I haven’t really messed around too much with the controls because it sounds good at the settings I use. I think it has an extra gain stage, I know it has an effect loop, and it has a foot switch to either switch more gain in or switch between the low/high inputs (I’m not exactly sure). I’m don’t know what the rest is. I think there’s an extra transformer in there? I took it back to Mr Ho in Vancouver, the tech that did the work originally, but he did it in the early 90s and doesn’t remember exactly what he did. Also he’s getting really old and isn’t particularly easy to talk to anymore. He is a local legend for amp work though so it’s bound to be interesting.

    I don’t know if these pictures are clear enough, if anybody wants close ups to certain areas, just ask. But in the interest of being able to use the end of its fullest I’d like to sort of know what everything is actually intended to do and I think the amp gurus here might enjoy the mystery.

    without further adeiu, here it is, Greg, my 1987 2204

    4F6B4883-872C-47C7-B74C-3F79D6ACD313.jpeg D61B7743-F70F-407A-84EF-280414F2EDFC.jpeg 80FE3EB3-8675-412B-AF16-271403B878B6.jpeg 3230CDF5-A617-4D6F-BDCC-8E688AEF4E3D.jpeg 9E78EF89-E7FD-4949-BCC0-116024A4F07E.jpeg 845AC0EA-A029-47B7-B4B7-4BC62EF423E9.jpeg 63B4F3E3-6039-42C4-BFA8-5A5CC54E9F50.jpeg 4FC928B3-9338-4060-B86E-4BEF297AD2DA.jpeg 2CA178E0-731E-43F0-8661-352DBA614460.jpeg
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Looks like a 12 year old tried to wire his dad's car stereo.
    Are you trying to put it back to stock?
     
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  3. South Park

    South Park Well-Known Member

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    So how does it sound . So what do you want to do hear
     
  4. South Park

    South Park Well-Known Member

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    From what I can see a lot has Ben done. This is more like a custom build not a mod job. You need to dial it in before you doe anything
     
  5. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Been in the hands of some clever clogs, the wiring is a joke, very third rate.
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    Look Ken, it sprouted an extra preamp tube. :ohno:

    3pre.png
     
  7. T0rch

    T0rch New Member

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    Well basically I want to try and understand what’s even been done haha. It sounds pretty good but I don’t use the channel switching or the extra drive, so for reliability’s sake it may make sense to just take it back to stock?
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    It looks like somebody added extra gain stages and channel switching.
    If you take it out, you will lose the extra gain.
    So that's the problem if you try to make it stock again...although the stock amp is really good.
    The other problem is finding somebody qualified enough to un-do the mess.
     
  9. Gutch220

    Gutch220 Well-Known Member

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    This thing would need major surgery to get back to stock, and if you already like then perhaps not messing with it is the best bet. If you put it to stock it will sound different. maybe you can try out a stock 2204 somewhere else to see if you like that flavor before you go down the road of back-to-stock. I think that'll be something where it will cost you a lot of money for somebody else to do it, or a lot of time if you wanted to do it and make a project out of it. I wouldn't touch it though to be honest. Once you drill 7 holes in the chassis you've kinda crossed the Rubicon.
     
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  10. T0rch

    T0rch New Member

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    This was sort of what I was thinking. Maybe I’ll have a tech look it over and make sure everything is fairly stable, albeit ugly, and just run it as it is
     
  11. clutch71

    clutch71 Well-Known Member

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    I'm no expert but it does appear to have a channel mod, gain mod, and loop with send and return . Does it change channel? Is it a clean/overdrive channel or is it more of an overdrive/lead channel? I'm in agreement with others, if it sounds good leave it. It might not be worth the cost to reverse the mods and still have all the extra holes to return it to stock.
     
  12. Gunner64

    Gunner64 Well-Known Member Premium Member

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    I wonder what kinda feeling one gets when they take a drill to the face of an amp like that..
     
  13. Gutch220

    Gutch220 Well-Known Member

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    I bet it's like skydiving, there's no return
     
  14. South Park

    South Park Well-Known Member

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    Some one should draw up a schematic on that amp
     
  15. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    I mean, I guess if it works fime, I can see not fiddling with it. It begs the question to me of why original owner didnt just buy a different amp? Get a 2205?
     

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