For some reason, still unknown, I had chronic hum issues with this build. I tried two different F5 cct. bds. and one Class AB module. Even modding the PS with an additional rec. bridge didn’t fix the problem. With large tranni and 132,000uf of high grade Mundorf caps there should be no hum. The other seven or so F5s I built were dead quiet.
Replacing the PS, tranni, caps, diodes etc with a SMPS of suitable power fixed the hum. But the SMPS would overheat and shut down. By adding a larger heatsink and a 12V silent fan running on 9V fixed the problem. The fan cannot be heard and now with large tranni removed the amp is much lighter.
The amp stays a Pass F5 build and does sound very, very good with good power, dynamics and bass extension. Usually I use it with one of my many tube preamps. A great combination and has given me many hours of enjoyment. It took many months of trial and error to get to this point but glad I persisted.
The enclosure I engineered from scratch around two very large heatsinks I had had for many years. My local metal supplier did all the plate cutting then I did a hell of a lot of drilling and assembling and re-assembling to get things right. The finished amp looks good and sounds better, once again, glad I persisted.
