Pass nation-repair caps for A-75

daly2k

Member
2005-08-11 3:55 pm
Well my 23 Year old Pass/Tharagard amp is starting to hum in both single ended and balanced modes and with the preamp connected but off.

I believe that the ps caps (40,000 uf per channel) are starting to leak and break down. They were not new when I first used them. I can't remember where I got them.

Anyway they are the computerized electrolytics that are the size of 12 oz beer cans. Two per channel. I have noticed in many builds and commercial amps that designers are going to plain electrolytics (some are bypassed with the politically correct fillm caps). I guess the advantages of these caps are;

cost
smaller size so more caps can be used

In your opinion is there any real difference in sound between the computerized caps and plain electrolytics? The rail voltage on the A-75 is 41 volts. I was thinking of getting the 50volt/10kuf panasonics and up the storage to 80,000uf per side.

I will take the beer cans out-fully charge them up and see if I can blow a northern pike out of the water. thanks, dave
 

daly2k

Member
2005-08-11 3:55 pm
Thanks everyone, I tried changing cables and shorting the inputs with no luck. It does hum louder in single ended mode than balanced. That led me on a ground loop hunt inside the amp and outside of it. No luck yet, I will put my scope on it and see if I can find the cause of the hum. I will hook up some other ps caps I have laying around in parallel to the existing ones to see if the hum dies down. I could have a cold solder joint somewhere or a loose connection. I do not suspect the driver boards as they are isolated with regulators from the Main supply.