From: trevor@home.net   
      
   "Christopher S"  wrote in message   
   news:Christopher.S.7dd76a8@audiobanter.com...   
   > My Adcom preamp has developed an intermittent fault, and any guidance on   
   > how to fix it would be appreciated. Can't really afford a new   
   > preamp/tuner.   
   >   
   > Basically, a high pitch tone is produced through the speakers (old   
   > school Heybrook HB1's....nice). The high pitch tone does not vary with   
   > an change in volume. I can make the sound come and go by pressing and   
   > releasing any of the buttons on the pre amp. Tone in/out for example.   
   > Even jiggling the headphone jack plug will do it. The sound does come   
   > back by itself though and the only way to make it stop is fiddling with   
   > a button of the preamp. Any idea what is going on?   
      
   Sounds like parasitic oscillation. The cause of that is harder to guess, but   
   most likely a leaky or dried out bypass capacitor. The fact that it doesn't   
   change with volume position is a clue that it's not in the input circuitry.   
   I'd look at all the compensation capacitors on any IC's after the gain   
   control first.   
      
   Trevor.   
      
   --- SoupGate-Win32 v1.05   
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