Bipolar voltage running the opamps.

The negative side isn't up to snuff.

Suspect a bad opamp here, since the other outputs are still healthy.

This is a job for a competent electronics service technician, as there are other things that could cause this, associated components to the output opamp for that output such as resistors, possibly capacitor, but the first thing to suspect is the output opamp, likely has a bad internal junction on the negative-going side.


--Mac

Would it have a separate op amp to the main amp, Mac? That is what is so puzzling. No bipolarity disorder on the main outs

Shouldn't the RCA outs simply mirror the mains?

I'd figured the mains would mirror the phono's as well!

I couldn't see an op-amp anywhere near the phono output, although there are some on the output board. Dodgy op-amp is the idea that makes most sense in all this.

Visibly the signal recorded from the mains doesnt look any noiser that that recorded from the phono, I'll check that toniqht,

Not necessarily.

If the designer did the breakout *before* the opamps that are used to drive each different output, a likely scenario, then there could be just one opamp driving the one set of outputs that is bad.

Schematic would be the place to find out, if one is available.


--Mac