Tech Square

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Turn off thump from power amp.

Posted by Cougar on May 10, 2011 at 07:48:09:
I had my amp repaired a while back after a preamp that passed -2.7 volts DC to my Edge M8 power amp (Older Black amp). The damage was major and all output transistors and input transistors were blown out. Long story short, I had the amp fixed by the ex-Edge repair shop in Boulder Colorado Edge Electronics. Unit came back working great except for the NEW turn off thump/pop I now get from it. The amp never did this before and now I can't get it to go away. I have electronics experience but this one has me guessing what it could be. The design is very simple Quasi Complimentary N channel bipolar output stage. From what I see of the parts on the board it looks like it has a basic Differential Pair with no current source tail. I have a feeling the problem is there and that the transistors were not matched properly in the differential pair and this is what is causing the the turn off thump now. I have adjusted the DC offset to very low level of 5mV. and the Bias has been set to 6ma per munufacturers instruction. But the thump is still there. I know the quick and easy fix is to incert a de-thump circuit but I want to keep the amp's sonics unaltered and adding a relay may add that. I just want to get the amp back original working condition cause to be honest... this is the best sounding amp I have heard and tried in my system. I don't have the schematics for this amp and I'm trying to get the from the manufacturer (Which would be a big help). If anyone here has had this type of problem and experience in fixing this? any help to guide me in the right direction will be greatly appreciated.

Thanks