Another worthwhile repair/upgrade

I've had my Parasound HCA-2200mk2 for about 6 months now. It wasn't perfect when I got it. It had a faint hum in the right channel. Supposedly, these amps are known for having humming problems. Some of that can be attributed to transformer hum, but that shouldn't be heard through the speakers if everything is working properly. My observation was that the transformer only made noticeable hum when you first power up and there was a current in-rush. The hum I was hearing was through the speaker.

I looked into the persistent hum it a week or two after getting it and looked like a cap or two was loose (cold solder joint), in the secondary power supply, so I tore it down. As suspected, I found a couple loose and re-soldered the joints and put it back together. The hum seemed to be gone. Well, when I was in there, I noticed the electrolytic caps didn't looks so good. I suspected there might be a leak or two because of some brown stuff that I could see. I planned to eventually replace all the caps in the secondary power supply (powers the input/pre section).

Well several months later, I started to notice the hum in the right channel again, so I started to figure out what parts I needed to change out the Electros. I talked to Parasound and Tony recommended that I change out a couple pair of small transistors too. Took awhile to spec replacement transistors because many of the parts are obsolete on this 15 year old amp. I did find some suitable replacements made by Fairchild and ordered them and 8 Nichicon HE and 4 PW caps to replace the old ones. Probably talking less than $20 worth of parts.

Did the job last night, took about 3 hours all told. Found out that my suspicions of leaky caps were correct. There was at least one leaky cap in each channel. The right channel was worse of course.
The caps in question are the light blue ones that are clustered together. Here is what they looked like before.




The caps used by Parasound were Richey, rated at 85 and as far as I can tell, the are probably rated at 2000 hour life. Over 15 years, that's only 133 hours per year or 11 hours per month. I'm sure this amp has seen more use than that, and 85c inside of an amp is not unheard of (that's 185F)
In my opinion, amps need 105 rated caps to be safe.


After the job...the Nichicons look much better, don't they?



The Nichicons I used are low ESR, high reliability. They are all rated at 105C and have a life of 8000-10000 hours at that temp, 4-5 times the Richey's. Hopefully, these should last the life of the amp.

Anyway, after changing all these parts out, the noise floor on the amp dropped to completely undetectable by ear. I mean, with my ear right next to the tweeter or mid, I can't hear ANYTHING until I turn on the preamp and a source. Before, I could hear faint noise from both channels, plus the hum in the right channel. The overall effect of this is a noticeable improvement in low level detail. Well worth the effort and minimal money spent.

Lesson here is that the electrolytic caps used in most amps will need to be looked at after 10 years. I'm not talking the large cans, but the smaller caps used throughout. They are cheap to replace and could give you great gains in your sound.

I next plan to go through the input board and replace all the E caps in there and remove some extra tacked on cheapy caps that were installed by Parasound in Taiwan (but not initially spec'd by John Curl). Mr. Curl talks about these mods over at DIY and Audioasylum.