using LM837 op amps
running duel power supply
pins 3,5,10,12 all grounded.
have power plug at one end, ground traces on outside edges(12+ & 12- run between) at pin 3 (12) I exit, connect to resistors then re enter under the chip via pin 5 (12) continue on to next chip (6 all in a row)
at end of row I connected the 2 grounds together as well as at the power plug end.
Maybe insert a couple of caps at the end (between 12+ to grd and 12- to grd.
a REAL ground loop.
If I figure out how to get a pic of the pcb layout I will post.