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JCM800, bright cap?

Discussion in 'Amps and Cabs' started by el34power, Jan 17, 2006.

  1. el34power

    el34power Member

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    All this talk about bright caps.... Do JCM800/2203 have...where..
     
  2. John Phillips

    John Phillips Member

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    If you mean the standard 2203/2204 single-channel Master Volume models, they have three: one 1nF (1000pF) on the Preamp Volume control; another 470pF across the 470K resistor that feeds it; and the third, also 470pF, across the 470K resistor on the next gain stage.
     
  3. el34power

    el34power Member

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    Yes..sorry. a 1984. 2203. How do these affect the tone. Any pictures, how to info?
    Been playing for 23 years.. not much of a techy..
     
  4. Roccaforte Amps

    Roccaforte Amps Member

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    Best advice, take it to a tech. Have him remove one at a time
    and you play it to see if its enough for you.
    these parts are used as high pass filters to brighten the signal,
    the trebble is where all your crunch is coming from.
    Removing these will thicken your tone, and also make the amp
    very dark sounding at low volume levels.
    Its a good thing to change if you're using effects, especially OD pedals.
     
  5. el34power

    el34power Member

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    Thanks Doug. I'm not a "moder" kind of guy... if it ain't broken... but the pre amp cap seems to be an easy "undo" if it turns out to be a bad thing. I usually run the pre at 65% and master at 35% with an OD in front (LTD,OCD,Picoso) to goose it up a tad.
     
  6. Roccaforte Amps

    Roccaforte Amps Member

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    There's a capacitor on the preamp pot,
    its an auto brightness circuit to compensate
    for trebble loss when the control is turned low.
    At about 3/4 rotation this part is out of circuit,
    the pot turns past it.
    You'll benefit more by having the high pass filter
    ahead of it removed.
    Again, you'll probably need a tech to get the right one
    out. If you're happy with your amp the way it is now,
    don't mess with, just play it!
     
  7. el34power

    el34power Member

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    I can hear it... past 70%...
    Point well taken on the moding...let it be...

    Thank you sir!
     
  8. cap'n'crunch

    cap'n'crunch Member

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    For anyone who might be interested, heres some instructions and pics showing which caps to remove. If your 2203 has vertical inputs as oppossed to the later horizontal input type then this will help you out.

    Heres the pics:
    www.tone-lizard.com/Ultimate_JCM800.htm
     
  9. el34power

    el34power Member

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    Thanks for the lynk.
     
  10. glogulus

    glogulus Supporting Member

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    A question regarding the link about the ultimate jcm800.

    I've done mod #2, and it helped a great deal on my 2203X.

    I am contemplating doing the 68K resistor replacement in mod #1. The author also mentioned placing another 68K on the 1MEG volume pot. However, does he mean the preamp pot (where I previously removed the capacitor) or the the actual volume pot?
     
  11. cap'n'crunch

    cap'n'crunch Member

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    Yes. Master Volume pot.
    He mentions putting a 100k resistor (not 68k) on the master volume pot. I've done this as well and you can definately hear more thickness at lower volume levels. So simple to reverse if you don't like it. Simply remove the wire from the middle lug of the master volume pot and solder a 100k resistor to the wire that you just removed. Now solder the other end of the resistor to where the wire was on the pot. You are basically just putting a 100k resistor between the MV pot and the phase inverter.
     
  12. glogulus

    glogulus Supporting Member

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    Thanks for the tip Cap'n! I'll try the 68K resistor first and see how I like it. Mod #2 though really helped with the high trebly sound. Did you do mod #1, what exactly did it do to the tone? I'm kind of digging it the way it sounds right now, so I dunno if I want to keep going.
     
  13. Dickie Fredericks

    Dickie Fredericks Member

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    Do these mods work on a 900? Ive got to run the treble and the presence at 1/2 or less cause its so bright.

    Richard
     

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