Thanks everyone for your help. Alas, no cigar;-) BTW, hum is not so bad that I cannot listen, but it is audible from 8-10 away during quite parts of songs.
@fineito- Not piling on at all. I'll try anything I can do easily this weekend and then call my tech and VAC on Monday.
@blindjim- upstream checks:
1. Hum not present when Atma S30 amp in system.
2. Hum present with 2 pre-amps (one active and one passive).
3. Hum NOT present on immediate turn on. I hear what sounds like a gradually increasing hum after 30--40 seconds. The relay clicks open a few seconds later and then the hum is very apparent in the speakers. It's possible that the first hum is coming from inside the amp. I assume that the first hum (maybe more of a buzz) is the sound of the soft start relay starting to open but I have absolutely zero knowledge of whether or not that is a reasonable assumption.
4. Hum present with multiple I/Cs. Have not checked speaker cables but seems very unlikely that the hum would be identical in both channels if it were hum induced in the speaker cables.
@almarg- I swapped in about 12 different 6SN7s in various combos. No impact on any aspect of the problem, so I THINK I can rule that out. Please disabuse me of that if I am wrong.
To all- I will try swapping out 300bs but it's also hard for me to believe that all 4 were identically bad, resulting in identical hum in both channels. Again, if I'm off base on that, please let me know. As I've said, I have ZERO technical knowledge of how these things operate.
@fineito- Not piling on at all. I'll try anything I can do easily this weekend and then call my tech and VAC on Monday.
@blindjim- upstream checks:
1. Hum not present when Atma S30 amp in system.
2. Hum present with 2 pre-amps (one active and one passive).
3. Hum NOT present on immediate turn on. I hear what sounds like a gradually increasing hum after 30--40 seconds. The relay clicks open a few seconds later and then the hum is very apparent in the speakers. It's possible that the first hum is coming from inside the amp. I assume that the first hum (maybe more of a buzz) is the sound of the soft start relay starting to open but I have absolutely zero knowledge of whether or not that is a reasonable assumption.
4. Hum present with multiple I/Cs. Have not checked speaker cables but seems very unlikely that the hum would be identical in both channels if it were hum induced in the speaker cables.
@almarg- I swapped in about 12 different 6SN7s in various combos. No impact on any aspect of the problem, so I THINK I can rule that out. Please disabuse me of that if I am wrong.
To all- I will try swapping out 300bs but it's also hard for me to believe that all 4 were identically bad, resulting in identical hum in both channels. Again, if I'm off base on that, please let me know. As I've said, I have ZERO technical knowledge of how these things operate.