I am assuming that TRV101 and TRV 201 are for setting the bias voltage.
Yes.
What is the other (TRV102 and TRV202) used?
The pots for fine adjustment bias.
https://www.diyaudio.com/community/threads/parasound-hca-1000a-bias-circuit
Parasound HCA-1000A Modifications
I recently completed some modifications to my Parasound HCA-1000A a few weeks ago, and HOLY COW!!! Now my $300 amplifier sounds like I spent easily 10 times that amount. It's amazing what can be done with a stock amplifier--especially one as good as the HCA-1000A.
Anyway, my question is this: I am thinking about writing a manual about modifying the HCA-1000A and offering it for a small fee--maybe even putting together a "kit" containing the manual and all necessary parts. Would anybody out there be interested in such a manual or kit, or should I not waste my time?
Anyway, my question is this: I am thinking about writing a manual about modifying the HCA-1000A and offering it for a small fee--maybe even putting together a "kit" containing the manual and all necessary parts. Would anybody out there be interested in such a manual or kit, or should I not waste my time?