This is not the only reason. One needs to create a reference node that is used by the input signal, the NFB loop and the servo. The second stage must seek its remote ground where the signal comes from; again this is the same as the input stage reference, so the NFB loop and the servo of the 2nd stage must use this remote ground. Now the load must be returned to the decoupling caps common point, because that's the point of least impedance for the output current loop. Parasitic currents are by nature spiky, contain high HF content. returning them via PCB traces or wires is inefficient.squarewave said: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.
Did I suggest that?But there's no reason for A2 LOAD to be connected to any grounds of A1.
EDIT: OK I made a wrong shortcut. It's the return of the OT that must be tied to the 2nd COM.
It does, but where? The most important factor is to make sure the output current loop is as short as possible and does not interfere with the 1st stage input.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
Agree. I should edit my previous post.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.