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Same Prosonic, Different Problem - ocillation/scratching noise on loud low note decay

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  • #16
    Thanks for hammering on me about checking power.

    While I did scope and meter the supply voltages at the tube sockets and circuit board (and every thing did look good), after listening to you guys it dawned on me that 1. I didn't monitor the supply voltages under a heavy load (leaning heavy on the tubes) and most importantly 2. I never pulled the electrolytic cover to physically inspect the big caps. Sure enough one is mildly spilling its guts.

    I can't say its fixed, the part is on order but hopefully this will take care of it.

    This site is valuable, especially to guys like me who tend to chase their tail. Really appreciate everyone's help with a special shout out to soundguruman for his constant support -- thanks buddy.


    • #17
      I think you have an open cap?


      • #18
        That would be my thought, never checked. Popped the cover and saw the leakage then went about looking for caps.

        Allied has been my source but they quit selling 500v caps. I checked a few other places and it was hit/miss.

        I ended up ordering some asian 105C caps (MIEC) from Studio Electronics in Burbank. I hope they work.

        Where to you source your electrolytics from?


        • #19
          Amp plays great. Went ahead and replaced the filter caps due to leakage but it turned out to be C11 (150pf silver mica) in the treble circuit. Since the noise only showed up at certain frequencies I continually hit the offending notes on a guitar while scoping the audio signal through the preamp. Clean going into c11 but the audio signal grew horns on the opposite side of the cap only when hitting offending notes, other notes sounded fine. Thanks again for everyone's help.


          • #20
            I had similar problems with a Prosonic. Ghost noise, microphonic inputs, crackling static even after guitar was disconnected from input. On the bench, just touching the inputs would create noise on front or back. I removed the 2 jacks, ran emery cloth between shunting switch paddles and the tip. Noise gone! Microphonic input SOLVED.


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