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What is the function of this .02uf capacitor in tremolo of Princeton Reverb?

Discussion in 'Amp Tech Center' started by doug, Oct 21, 2020.

  1. Oct 21, 2020 #1
    doug

    doug TDPRI Member Silver Supporter

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    Just wondering what is the purpose of the .02uf capacitor I circled in red in the image I attached.

    Thanks.
     

    Attached Files:

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  2. Oct 21, 2020 #2
    Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Smoothing the output of the tremolo.
     
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  3. Oct 21, 2020 #3
    tubegeek

    tubegeek Friend of Leo's

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    ... by shunting high frequencies to ground and leaving low frequency oscillations to go through the larger (.1) cap to the intensity control. Filters out noise & any "spiky" frequencies in the tremolo oscillator.
     
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  4. Oct 21, 2020 #4
    D'tar

    D'tar Friend of Leo's

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  5. Oct 21, 2020 #5
    Ten Over

    Ten Over Tele-Holic

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    The .02uF cap in question and the 1M resistor that it is connected to form the high-cut portion of a bandpass filter. The .1uF cap and the 250K Intensity pot form the low-cut portion.

    When the high cut-off frequency gets close to the low cut-off frequency, the signal that passes becomes attenuated as compared to signals with the cut-off frequencies well spaced. The cut-off frequencies with the Princeton tremolo are very close, so the tremolo signal is attenuated in addition to having a limited bandwidth.
     
  6. Oct 22, 2020 #6
    doug

    doug TDPRI Member Silver Supporter

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    Thanks for all of your answers. I asked the question after reading the following in https://guitar.com/guides/diy-workshop/diy-workshop-rift-amp-mod-part-2/

    Between the 1M resistor and 0.1uF capacitor, there’s a 0.02uF capacitor that’s tied to ground. It’s not there in the brownface trem, and de-soldering one end of the capacitor seemed to give the Rift’s trem a stronger feel. I decided to remove it, but do so carefully because it will come in useful for the next stage.​

    While I supposed I could just lift one end to hear the results, I was wondering what downside might exist by removing the .02 capacitor.
     
  7. Oct 22, 2020 #7
    Ten Over

    Ten Over Tele-Holic

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    See Reply #3.

    Sometimes the LFO will oscillate at higher than tremolo frequencies even when turned off by the footswitch. The .02uF cap will shunt those frequencies to ground so that they don't show up at your bias.

    You can get a little more intensity by removing the .02uF cap, but there are other ways to do it without losing one of the functions of the .02uF cap. Those guys at Fender actually knew what they were doing and they wouldn't have put an additional component in an amplifier unless they had a good reason. But go ahead and try it. That's what the guy that wrote the article does.
     
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