Purpose of the "fizzy" (PI) cap?..

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by BluePat, Feb 24, 2009.

  1. Feb 24, 2009 #1
    BluePat

    BluePat Member

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    and by altering the value, what does that do?

    Pat
     
    BluePat, Feb 24, 2009
    BluePat, Feb 24, 2009
    #1
  2. Feb 24, 2009 #2
    RussB

    RussB low rent hobbyist Silver Supporting Member

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    It's there to supress high frequency oscillations

    The higher the value, the more high frequecies will be diminished. In Marshall circuits, I have gone as high as 180pf and couldn't hear a difference from the stock 47pf cap. I could hear a 250pf cap
     
    RussB, Feb 24, 2009
    RussB, Feb 24, 2009
    #2
  3. Feb 24, 2009 #3
    BluePat

    BluePat Member

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    Thanks Russ :BEER
     
    BluePat, Feb 24, 2009
    BluePat, Feb 24, 2009
    #3
  4. Mar 1, 2009 #4
    cap'n'crunch

    cap'n'crunch Member

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    Whatz you guys talking about? My 2204 is fizzy at low volumes. Is this a remedy for that?
     
    cap'n'crunch, Mar 1, 2009
    cap'n'crunch, Mar 1, 2009
    #4
  5. Mar 2, 2009 #5
    donnyjaguar

    donnyjaguar Member

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    The capacitor reduces the gain of the amplifier at frequencies above its normal operation due to phase reversal through the output transformer. To my knowledge its not a "tone shaping" component and RussB's experiments bear this out.
     
    donnyjaguar, Mar 2, 2009
    donnyjaguar, Mar 2, 2009
    #5

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