Parasound HCA-1000A Modifications

I was looking at one of these with modifications in mind - Did you mod and test as you went? I would be willing to bet a capacitor refresh and wire made the biggest difference. $100 all in on parts, I was considering $100 on new cable alone - signal and speaker. It's a shame on this model that signal runs to pots and back.

The pots are not the weak point, run the pots wide open and they are mostly out of the circuit. One of the weak points are all of the cheap film caps used through out the amp. The other is the off brand lytics that were used. These amps are old enough a general cap refresh would not hurt.

And you can go nuts with Vishay resistors replacing every resistor in the signal path. Also depends on how good your source and preamp are. If not up to the task then you may not hear much of a dif. 

At the end of the day you can dump 500 bucks or more into vishay resistors and other parts but you'll still have a 200 dollar amp. Once you know what parts do, no need to test, did that on the first one. There is no resistor on the planet that sounds better than a Vishay, but they are not cheap. Expect to pay 12 to 25 dollars per resistor vs. 69 cents for many metal films.  

I have HCA-1000A that was fully recapped, but setting the bias is different story. There are two pots per chan. and three test pins. Not only what are test pins for but mine has two / channel (TRV101, TRV102 and TRV201, TRV202). I am assuming that TRV101 and TRV 201 are for setting the bias voltage. What is the other (TRV102 and TRV202) used

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