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robgilmo 31st March 2012 09:58 PM

Would this be OK
to test the bias settings and dc offset in an amplifier?


tvrgeek 31st March 2012 11:55 PM

It looks fine. Bias is normally set at about 125 mA, sometimes more, sometimes less.
As it is DC, you don't need to worry about the poor frequency response of a non-true RMS meter. If it is a BJT amp, you are usually just measuring voltage across the .22 Ohm emitter resistors. If a MOSFET sometimes you replace a fuse with the meter and read current.

You should not be adjusting offset. It should be designed in. Sometimes you can adjust symmetry, which to do correctly required a spectrum analyzer or distortion meter.

robgilmo 1st April 2012 08:09 AM

Thanks, I have read that it does no harm to test the offset at the speaker terminals.

tvrgeek 1st April 2012 12:13 PM

No harm and a smart thing to check. But, do you know how much you should tolerate? How it changes with the amps temperature? Be careful looking for trouble where there is none. "don't fix it if it ain't broke"

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