Parasound HCA-1000A Modifications

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

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

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 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.

@south43 , was not an amp I did. I did not use solen caps. Have to be careful with the solens, they can end up sounding lean and thin in the midrange. 

Avilex ! Did you ever end up making these guides/kits? I would be interested in 1. Or  if you or anyone in the group can send me some info, that would be lovely. I know this is a super old thread but figured I'd give it a shot. I think a series of these guides/kits for different "mid fi" amps would be a great idea. My nad 2200 comes to mind as well! 

A older thread yes but these older parasound amps are special and I'm certain with mods there even better. I also have the HCA-1000a and a HCA-800 that I upgraded my self with all new Nichicon caps. Wasn't expensive at all and made an Audible improvement plus extended the life of the amp. Still have both amps and I am enjoying them. It is important that you keep the replacement caps at the same values except you can use a cap that is rated at a higher voltage but the capacitance should be as close to the same. Only use exact replacement caps and pay attention to whether they are non polarized caps or polarized caps.

Me as well- panaseef
the Parasound HCA series is still a very good amp in 2017.
Happy Listening!

Very old thread, but I have an hca-1000a and would be interested in learning about these mods.  Contact me!

I am in need of a faceplate for a Parasound HCA-500 amp. Does anyone have one of these for sale or know where I could get one?

This reply is for Avilex or Johnss. Though this thread is old I might have one of your modified amps. The 1000A I have has solen caps, silver wiring, dampning of the chassis and top plate, the loop rca's disconnected and volume pots have been removed. The previous owner did not know who did the mods. I stumbled on this thread while copying a review. If any of the names mentioned performed the excellent mods on my amp please let me know. I can provide pics to further id the mods done. Happy listening!

still have that kit around, Avilex?

I think there may be a limited market for this. I agree, I have modified a number of Parasound amps including the 1000a.
Very nice sounding amp modified. I replaced over 30 parts on the main board, added new soft recovery bridges, etc.

One gets similar results on the 2200II and 3500 amps; have not tried the new JC1s or other series.

JOhn

If that was your cost for parts and you assembled an easy to use manual $250 would be a fair price for manual and parts. $75 would be fair for just the manual. i don't know that there would be many takers at those prices though. $200/$50 would be an easier sell.

Good luck!

To Chadnliz: I haven't been inside an HCA 800II, but I'm sure that there is plenty that can be done with it. One look at a schematic and I would have a pretty good idea as to what you could do.

To Rcziech: The modifications involve disassembling the entire amplifier and replacing stock components. I'm not getting into altering the actual circuit or replacing sections of the circuit board, necessarily. These mods could be done by anyone with a RadioShack soldering iron and desoldering tool. The only other tweek involves rebiasing the output devices (which is much less difficult than it sounds), which does require a voltmeter; but this tweek isn't absolutely necessary. I'm not sure what I would charge, though it wouldn't be exorbitant by any means. It would take a bit of work--I'd have to take high-quality color digital photos, create my own schematic diagrams, and make sure it was written well so that it was easily understood and followed. I was thinking that it would include a short primer on soldering and desoldering technique, a step-by-step guide to disassembling and reassembling the amplifier, as well as instructions on modifications, parts list, and a list of sources (with approximate prices, as they change with time) to find the parts at. All of these sections would have color photos to guide the reader along the way. What do you think a reasonable "fee" would be? Notice that I am NOT asking what you think it "should" be worth, but how much do you think people would pay?

By the way, the reason for my considering a "kit" is because I have been able to get the parts I use at very low prices compared to what you would normally find. This saves the "tweeker" money (in both price of parts and separate shipping fees), as well as the hassle of tracking down all the parts. There might be some things I could do with supplying very nice wire as part of the kits also, but that remains to be determined yet. Of course, high-cost items (like WBT binding posts & RCA connectors, etc.) would be optional.

To Myraj: I replaced a good number of stock components (capacitors, resistors, bridges, output devices, wire, connectors, etc.) with much higher quality parts. The result is greatly improved sound. The catch is that you have to know what parts to replace, what parts to use instead, and where to find them at a good price. I don't remember exactly what I spent on my parts--I'd have to add up the receipts to be exact--but I think as a ballpark I spent about $100 including shipping fees from several different shippers, and I replaced a bunch of parts.

I think it would depend on your definition of "small fee".

Also, the difficulty level to do the mod would be a factor.

What did you change? How much were the cost of parts?

can the same upgrades apply to my old HCA 800II?