Well, there's hum and there's humm. Using a butt set you will detect some low level hum on a 601 power supply directly off the AB AG terminals. It should be low enough (approximately 1 VPP) to be audible across AB AG, however, when the voltage is applied to a card, there are additional filter capacitors that take out the ripple altogether. If you have a scope, check out the level of ripple that you have. It's all power supply. There is nothing else (except a defective card, which I assume you have already eliminated as a possible source of the ripple) that can cause hum in a 601.
Rcaman
Rcaman
