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Old 24th March 2007, 01:48 PM   #1
GordonW is offline GordonW  United States
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Join Date: Mar 2005
Location: Marietta/Moultrie GA
Default ADS PQ20 amp- anyone worked on?

Got a working ADS PQ20 amp... it's fine, except it creates ground loop noise (alternator whine) with EVERY component combination its been connected to.

I have a FAINT memory, of someone once telling me that there was an isolation diode (or cap, or whanot), between chassis ground and signal ground... and that the diode/cap/whatever could be blown, by operating the amp with a bad main ground... at which point, the chassis ground would short to signal ground... voila, ground loop...

Can anyone either verify or debunk my recollection? And if it's true, any clues on WHERE the little bugger is in the amp?


Speaker Design, Restoration and Repair- since 1985.
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Old 24th March 2007, 08:14 PM   #2
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Location: Louisiana
I'm not sure about the ADS but some amps have a diode between the chassis ground and the audio (RCA shield) ground. When the diode shorts, it will cause ground loop noise. If the amp had a direct short between the RCA shields and the chassis ground, it's likely a shorted diode. If the resistance between the two grounds is relativly high, the problem is likely something else.

Does it play without noise on the bench?
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