amplifier KA-5090R - strange circuit in the Kenwood KA-5090R amplifier - Repair

[dreamth]

I think it's clear that the op-amps cancel the ground current from the feedback networks, but the question remains, why? It seems as though the input ground and output grounds are not wired separately as they should be? I suspect that the effect of removing these op-amps would be subtle, unless you knew exactly what to look for.

May be just a simplification of their earlier sigma drive systems to enhance the damping factor...? That might explain the summing of R207 with R155 as an attempt to counter back emf... DF= 250 is an impressive figure for such a simple design. Just guessing again, but that would be indeed subtle.