Hi, just a quick question. On my amp the R channel has >200 mV DC offset with the input shorted, is this too high? With the preamp on the input and no input signal on the preamp the offset is almost 0. This confuses me. Can anyone explain this?
I'd guess the amp does not have an input coupling cap to prevent DC. I think some of the "direct coupled" amps back in the day did this. What happens if the amp input is unconnected? Pure guess, bias current voltage generated by resistance mismatch(0 ohm by the short on input side and probably around 1K on feedback side) of the input diff pair of the amp.
Does the preamp have a DC offset on the R-chan output? Depending on the gain of the amp at DC, it would be around the same but the negative as the output offset if amp dc gain is 1, nulling the amp offset. At this point, shooting in the dark without a schematic showing pre out circuitry and amp in.