Bridged OPA541 amp humming

[kinser]

Hi all,

I built about 2 months ago a powered subwoofer using 2 OPA541's bridged, now it had some problems and i fixed them today, but still have the humm... I have checked for any ground loops but didnt find any, but then while the amp was on, and playing music I touched the heat sink and the humm dissapeard! but, but... the OPA's share the same heatsink and are not isolated, because the tab is the -Vs, but when I check to see if there is any kind of connection between the tab and the -Vs pin (on the data sheet it sais there is), there is no connection.

So what do I do?? do I ground the heatsink? well I cant because the chips are not isolated and the -Vs should be going through the tabs, so again, what do I do?

Thanks,
Kinser

 

[Russ White]

I think I would isolate the chips.

 

[kinser]

Russ White,
Thanx, I will do that, but i would like to know why is there a hum, because both tabs are V-

Thanks,
Kinser

 

[Russ White]

I am not sure, but I have seen the same sort of behaviour out of LM4780s and that solved my problem. Wish I could tell you why.

 

[kinser]

Hey Russ White,
Thanx anyway.. I'll go tmrw to get some mica or somthing...

Thanks,
Kinser