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PRS treble roll-off question

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by devbro, May 17, 2005.

  1. devbro

    devbro Member

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    Hi everyone,

    I searched the archives and found a few posts on this issue but I'm a total electronics newbie and still not clear.

    I just got a new amp and now I notice a huge lose of treble when I turn down the volume. The reduction happens between 10 and 8. In fact, by the time it's at 8, it sounds like mud. I'm using fairly high quality short cables (Mogami 2524) and a buffer on my pedal board so I dont think its a cable capacitance issue.

    I opened up the back of my PRS and found a cap (I think it's a cap) marked 180k soldered across the lugs on the pot.

    What can I do to make it so when I turn down the volume, the treble / tone remains intact?
     
  2. Taller

    Taller Silver Supporting Member

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    That cap is there to prevent what you're describing.

    You say you just got a new amp - have you tried the guitar through a different amp?
     
  3. devbro

    devbro Member

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    Hi Taller,
    I'm now playing through a Bogner Shiva. Oddly, I never noticed any treble loss with my Mesa Triaxis.

    Could the cap in my PRS have gone bad?
     
  4. Taller

    Taller Silver Supporting Member

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    Highly unlikely.

    If the guitar sounded fine through the Mesa and not fine through the Shiva, my best guess is the way the different amps are reacting with that guitar.
     
  5. devbro

    devbro Member

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    That's what I think too.

    I think I need to change the cap to a different value.
    Any recommendations?

    Thanks.........
     
  6. John Phillips

    John Phillips Member

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    Are you totally sure the cable from the guitar to the pedalboard is OK? If the pedalboard is buffered, it's unlikely that anything after that could have such a drastic effect... if it goes really muddy just by dropping from 10 to 8. Is the buffer the first thing the signal hits on the board, or is there a pedal first (which could have significant capacitance too)?

    If you do want to try different cap values, start with a 500pF. Anything less won't make that much of a difference compared to the 180. You could also try fitting a resistor (start with about 220K) in parallel with the cap - this will reduce the steepness of the pot taper at the top end, although it will also reduce the volume drop, which may not be what you want.
     
  7. devbro

    devbro Member

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    Thanks John,
    I checked all cables and they're good. My signal chain is as follows:
    guitar > wah > buffer > fulldrive > chorus > trem > delay > volume pedal > amp.

    I soldered a 220K resistor today as you suggested and it helped. I put it between one leg of the cap and the associated volume lug.

    It's still not optimal but it's better than it was...
     
  8. devbro

    devbro Member

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    The Bogner is soooo much more responsive and articulate than the Triaxis. I too beleive it's simply that the Triaxis was coloring the signal. I was hoping that there was some simple solution to minimizing the treble loss when turning down the volume on my guitar. The resistor helped allot but I think there's more to be had by fiddling with different values. I'd bet that with the right cap and or resistor, I could eliminate the treble roll-off entirely.

    Having just left the rack world, I'm struggling with the inherent issues with a head and pedals and yes I'm still struggling with the pops I get when switching pedals. When I finally solve these 2 issues - and I do beleive they can be solved - this rig will smoke anything I've ever played through.

    BTW, everything on my board is true bypass except my Line 6 echo park delay that is last in the chain. The Wah is a Teese RMC3.

    You guys are really helpful and I'm so lucky to have stumbled on to this board. :D
     

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