Marshall JCM 800 4010 capacitor question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by texgrind, May 13, 2008.

  1. texgrind

    texgrind Member

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    Hello -
    I have an '83 Marshall JCM 800 model 4010 (which is the combo version of the 2204) that I use as a head. It's almost identical to the 2204 except that it has a capacitor across the middle tone pot. Apparently Marshall did this to revoice the heads as a combo. I'm not sure exactly what it's removing, but the amp does sound a bit darker/thicker with it. In fact in it's current form I actually prefer having the stock brite caps in place.
    The cap on the mid pot is a 4n7 cap - so that's 4700pF. I removed it to hear what it sounds like in "head" form and it was a little bright for me...I definitely prefer having a capacitor there. I always get confused about how going up/down in value affects tone. If I'd like to still keep a cap on the mid pot but have it split the difference between the current sound and the sound with no cap what value should I use? Is it as simple as trying something around 2400pF to get right between 0 and 4700?
    Thanks.
     
  2. jay42

    jay42 Member

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    Yup. Get a few values like 1000, 1500, 2000, 2200, 2700, and 3000pF. Is it mica (looks like a brown chiclet) ? (Those are actually a bit pricey.) Polyester film is fine in that range. www.mouser.com for M150's at .001, .0022, and .0033uF. Search on 539-150102J630AA or look for page 818.

    Clip off the 0.001uF on the PREAMP volume pot first, assuming it's still there.
     
  3. texgrind

    texgrind Member

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  4. jay42

    jay42 Member

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    Even cheaper...yes, the type of cap will change the quality a bit. It's worth a few bucks to try film and ceramic caps. It's impossible to know which you'll prefer. You just tack them on without cutting the leads, then listen.
     
  5. strangec

    strangec Supporting Member

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    I thought the 2204 and 4010 were the same?
     
  6. jamme61

    jamme61 Supporting Member

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    I like the cap too. You don't have to use a expensive cap there. The cap beeds off signal to ground.
     

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