Modding jcm800's

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by tbone666, Mar 15, 2010.

  1. tbone666

    tbone666 Member

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    I know some if not most will say this is a sin but there is a tone I'm after that I believe the modding process can help with.

    I want to put in a high quality tube fx loop plus I want the treble to be less spikey. I believe that's the technical term.

    I checked out Voodoo Amps and FJA mods. Any others out there that I should look into to? Also, I'm near Chicago so a local tech that specializes in Marshall would be a great point in the right direction.
     
  2. jerrydyer

    jerrydyer Member

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    metro amps in michigan has tube loops and solid state loops. join that forum and read up on it. I have both if you want someone to do it for you
     
  3. gretsch58

    gretsch58 Member

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    you could also contact Frank Levi or Tim Caswell in NY.
     
  4. 02Singlecut

    02Singlecut Member

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  5. Ronsonic

    Ronsonic Member

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    What model is this, four digit number, please?

    If it's the usual master volume 2203/4. There is a bright cap to be snipped without hurting your conscience or resale value.
     
  6. sfx

    sfx Member

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    I assume you already own the amp, but the reissue 2203x comes with a loop stock I believe.
     
  7. IIIBOOMERIII

    IIIBOOMERIII Member

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    There are some simple things you can try yourself.

    1st - Coming off the input jack is a 470 pf cap and a resistor, this is called treble peaking circuit. If you remove the cap this will help your tone.

    2nd - Clip out the "Brite Cap", there is a cap hanging off the back of the volume control, clip out the .001uF capacitor across the Volume control.

    There is plenty more you can do here.

    http://www.tone-lizard.com/Ultimate_JCM800.htm


    I wouldn't add an effect loop if I were you if it is a true 80's JCM 800.

    If it is a 2203 try pulling the 2 outside tubes, this will drop it to 50 watts and break up quicker.
     
  8. darkbluemurder

    darkbluemurder Member

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    It is probably enough to clip out the bright cap on the preamp volume control.
     
  9. HipKitty

    HipKitty Silver Supporting Member

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    I totally agree..though I've modded enough of them over the years, I was glad to see one of my artists bring in his 2204 that had a couple of Jose (you know who this guy is...) mods and had me convert it back to stock. A commendable act on his part knowing that with it's mods in place, the amp is worth some dollars simply because the mod installer.
     
  10. drbob1

    drbob1 Silver Supporting Member

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    If it's a later 2203 (like my 86 2204s) the bright cap is C5 on the PCB. You can remove the knobs, unbolt the pots and the input jacks, gently push the PCB backwards and desolder one leg of C5. That way you can return to stock if you're not overjoyed with the change. You can also change values (I think the PlexiPalace forums have suggested values). That'll get rid of the peakiness. Tube changes can make a huge difference, too. I switched out the JJs for a nice set of Siemens EL34s and changed preamp tubes to a mixture of RFT (darker) and american tubes. Nice results so far...
     

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