abbey road d enfer said:
Replace the "ground" connections with the actual resistance they present and you'll know why I wouldn't reference anything to the "filter cap ground of the power supply."
That's not helping me see what you're saying. Just explain what loop of components / grounds would be created that would cause noise / instability.
This issue makes me think of those ground plane inductance videos boji posted where the return follows the trace over ~1KHz even though there's a more direct path back to the supply. Those videos explain
why low impedance bypass caps need to be right next to the source and not at the power supply.
So taking that into consideration you are right about R6 returning to A1 COM because most of the output current of A1 is coming form FB and not LOAD. So I have to revise my original statement to try running R3, R6, A1 COM and BLK on a separate ground. But there's no reason for A2 LOAD to be connected to any grounds of A1.
Also, with a careful layout it should not be necessary to use a separate ground wire. I was only suggesting that because the poster was experiencing oscillation so decoupling A2 LOAD from A1 +IN could have helped.
But still, in this particular circuit, I believe it might actually be better to use a separate ground for R3, R6, A1 COM and BLK because A2 LOAD throws a lot of current around so there might be an advantage to giving the parts on the input (R3, R6, A1 COM and BLK) a separate path to supply ground.
abbey road d enfer said:
Agreeing to disagree is not constructive. Having diverging opinions on a same subject from two knowledgeable persons is disturbing for other members.
If you think I'm saying something incorrect then by all means go ahead and say so. I'm a big boy. I could be wr-wr-wrong. I have been wrong before and when I realize I am I admit it. I just don't understand what you're saying in this case. You say connect transformer BLK to A2 COM? That makes zero sense to me. BLK is just for shunting common mode noise to ground. Capacitively coupling the +80dB output of A2 LOAD to A1 +IN through the transformer shield does not seem like a good idea to me.