Variable Bright switch mod for Pro Reverb?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Clear Guy, Mar 22, 2006.


  1. Clear Guy

    Clear Guy Member

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    I am wondering if the following could work as a mod on my silver face Pro Reverb:

    I want to add a small potentiometer in the place of the 2nd input jack on the reverb channel (which I dont use) and wire it in series with the bright Cap and then to the bright switch. The potentiometer would act as a variable resister to govern just how active the bright cap/switch would be.
    I have not determined what value Pot to use for this mod.

    Maybe someone might have some suggestions on a better way to do this?
     
  2. gtrnstuff

    gtrnstuff Member

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    I used a 1.2M in series with the bright cap on a 1M vol pot once. So I'd start with a 1M and see if it does the trick. Cool idea, variable bright.
    Experts chime in 3...2...1...
     
  3. Clear Guy

    Clear Guy Member

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    thanks gtrnstuff.
    The cap that is in there now reads 100M 1KV. I was going to try a 500K pot first but the 1 Meg is the way to go.

    Anyone else?
     
  4. Clear Guy

    Clear Guy Member

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    Have not had a chance to try it yet. I was trying to get some feedback before i dove in head first.
     
  5. bob-i

    bob-i Member

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    I don't think a pot will be very effective. I may be wrong so try it, but what I'd do is put in a multi position switch and a variety of caps.

    100M is 100pF so you'd most likely want some smaller. I'd try 68pF, 47pF and 22pF. If you want more brightness you could go with a 120pF or even as high as 220pF although that would be overly bright.

    Another choice is using multiple treble caps in the tone stack to shift the range of the treble control. I believe that the treble cap is 250pF, lowering it's value would brighten up the amp so a 180pF or 120pF would make the overall charactor brighter. Raising the value would give you more mids. 330pF or 390pF can give you really nice fat mids.
     
  6. donnyjaguar

    donnyjaguar Member

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    My advice is to try the modification with the amplifier apart. If its worth bothering with then put it in permanently. I often noodle around with things on the bench but decide not to bother as they just didn't do it for me.

    I don't see any reason why you couldn't put a 1M pot in series with a higher value capacitor (say 250pF) and see what that does. The values in question are so low you could actually use an old variable capacitor to try different things. The only danger I can see with this is if either side of the circuit is live so you'll have to be very careful. Probably in the case of your amplifier.
     
  7. Clear Guy

    Clear Guy Member

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    Great to get some good feedback. Thank you all.
     

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