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My 2204 mods - done

Discussion in 'Shock Brother's DIY Amps' started by JohnnyCrash, Oct 2, 2009.

  1. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Mar 12, 2005
    Fullerton, CA
    This one is especially for Ben Harmless and 11 Gauge.

    I finally got my 2204 tweaked to taste and figure I'd share my setup and thoughts on it for any JCM800 fans out there.

    1st I installed another 12AX7, 12VDC transformer, and 12v DPDT relays for two all-tube footswitchable channels.

    Here are my current mods:

    1. Hotter 34k input grid resistor.
    2. 1st stage cathode 1.5k with a 1.68uF bypass.
    3. 2nd stage cathode is 5k.
    4. 235k resistoron both channel's plate feeds to the Pre/Gain pots, removed the 500pF treble peaking caps (sounded too fizzy/whimpy with them in).
    5. Channel 1's Pre pot is a push-pull DPDT switch as a Soldano SLO-100 style Clean/Dirty switch (a 470k in series with a 39k splitter to ground to dampen the extra cascaded gain in Clean mode).
    6. 235k input grid resistor to the tonestack tube with a 500pF treble peaking cap (sounded dull without it).
    7. Tonestack's cathode is bypassed with a 4.7uF.
    8. Tonestack's Bass cap is 0.1uF.
    9. 0.1uF couplers used from PI to power tubes.
    10. "Plexi" style Presence circuit (47k to 5k pot), instead of the JCM800 Presence control.

    As you can see I trim the attenuation between certain stages (increasing gain, using 235k instead of 470k), add gain (1.5k) and fatten up the preamp cathode for more mids (1.68uF), add gain at the tonestack (with a 4.7uF bypass), give the tonestack more Bass on tap (0.1uF tone cap), give more bass to the power section (0.1uF couplers after the PI), and used a slightly raunchier plexi-style Presence/NF circuit.

    My footswitch relays have 10M resistors from any plate caps to ground to reduce footswitch popping/noise, but I still have a little bit (I'll hopefully iron that out soon).

    I know, "that's a ton of gain increase for such an already gainy amp." I wanted more on tap for extreme projects/tracks I might have in the future (I don't have any Mesa Triple Rect extreme style amps in my studio), but when I dial the Pre knob back - I'm still in the 2203/2204 JCM800 range. not too fizzy, and much better than stock JCM800's with my increased mid mods.

    Channel #1 - Push/Pull Pre knob fro Clean/Dirt. Nice warm cleans or an identical dirty setup to channel #2.

    Channel #2 - sounds great all the way along the Pre knob.

    Footswitching - I still have a moderate (but not terrible) pop when changing channels. The relays give me seperate Pre and Master volume controls sharing one tonestack and split where the signal goes (unused preamp tube's grids are grounded, routes the input, Pre pots, Treble pot relays into MV, MV relays out to PI).

    This thing is closing in on being my favorite Marshall build - my plexi50 is still too badass for my 2204 to catch up to though (those mods are for another thread)... for live work, an all-tube 2 channel JCM800 with more bass and mids can't be beat though!!
  2. Ben Harmless

    Ben Harmless Friend of Leo's

    Mar 10, 2003
    Allston, Mass
    Well done then, sir.

    I'm particularly interested in the presence circuit mod. I may look into that one myself.

    I just plain don't need more dirt though. I actually look for excuses to use less these days. I play occasionally with a band that's into a "heavy" sound, while I tend to want more of a "rockin'" sound. I think folks here know what I mean.
  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Mar 12, 2005
    Fullerton, CA

    I know what you mean. To me, the holiest of sounds is ACDC's Back in Black album, and the gain is much less than the song's/production vibes put out. Its musical, chiming, piano-like, and syrupy sweet...

    I was concerned my tweaking would make this amp one sided, which truthfully didn't bother me that much since I had my plexi50 as magical as any Marshall could possibly get (too beautiful to describe). The thing is, I can dial back the Pre and get that huge ACDC sound still (something my original 100w 2203 from the early 80's could only do when ear splittingly loud). I can't get Ministry or Marylin Masnon or Rob Zombie tones with the amp on its own (still needs pedals for that), but I can get a bit more "umph" and singing sustain than a typical JCM800 - with more mids, chime, and mellow chirp than an original. Its not a Triple Rect, but its more flexible, complex, and soulful than ANY JCM800 I've heard - and it can go a bit heavier and overdriven. I'd comfortabley put it against the best of the best.

    Anyway, as much of a high gain 2203/2204 junky as I am, I still can't get my JCM800 to fully match my plexi50 in TONE (though its damn close now). Its magical, complex, and huge... nearly where my 2204 is now.
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