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What causes an amp to discharge a thump.?

I have installed a Quad 909 amp in my system amd ever since when it is shut down I here a slight thump or like a statice discharge through the speakers.
This takes any where from 5 to 8 seconds .
The order in which I turn off the equipment is the reverse of turn on, that is amp first preamp next then source.
I'm sure it is coming from the amp, but why?

Thanks for your help.
wnegele

Showing 1 response by aball

aball
2,018 posts
 
Your main caps are dumping at turn off. I have fixed that problem in amplifiers by using bleeder resistors to ground. It totally eliminated the thump but requires soldering and some circuit knowledge to do the job risk free... If you can overlook it, it is fine and shouldn't hurt anything. Several older amp designs I have come across do this but some newer ones do too. The best way to solve the problem, from the designer's standpoint, is to put in a relay and muting circuit - but that costs money.

Arthur
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