Counterpoint SA-2000 Hum

I recently purchased a Counterpoint SA-2000 off of ebay and it sounds fantastic.  However, it has a hum problem.  I used a cheater plug and it reduced but did not completely eliminate the issue.

Per the manual, I should be able to adjust the DC offset, but when I popped the top, I found the unit had already been significantly modded and I suspect the work was done by the old Alta Vista folks.

Looking at their old website, I see most of their mods were completed on this unit.  The coupling caps were upgraded, the buffer circuitry was eliminated, the rectifier was changed, some electrolytics were replaced and others upgraded to the Continental oil caps, and 5 pairs of RCAs were upgraded.

As part of those upgrades, the pots to adjust the DC offset were removed.  So, what can I try next to eliminate the hum?



Post removed 

They are removed because the whole Opamp buffer stage is removed and its just the plate of the 6922 driving the output.   

You will need to check the B+ voltage top of both the plate resistors likely modded to Mills 5W wirewounds around that tube.  I recall the B+ is supposed to be 240V and the plate voltage is supposed to be around 70V.  

If the regulator zeners on the right hand side of the board are blown the 240V wont be clean and it will be quite a bit higher and you will get hum.

If you are in the SF Bay Area I can help you take a look.

My first Audiophile preamp and amp was the Counterpoint SA2000 line level pre and the Counterpoint SA 220 in 1990 Loved them both. Never had a problem with the SA 2000 but the SA 220 my L ch MOSFET went and that was that. 🤷‍♂️.