Hum can be induced by a nearby transformer from another piece of equipment or simply a power cord position or i/c position. Have you tried 'cheater plugs' for your AC power?
Shorting Plugs and Non-shorting Plugs - Wothwhile?
Well, I have a hum that I can't isolate. I've tried all the usual fixes with no luck. I am convinced, however that the problem is interference from some other device (that I can't isolate). I have a bunch of cheap interconnects that I could use for open RCA connectors on my preamp (Tape 1, Tape 2, Tuner, etc.). Is the effort worth it? I certainly don't mind sacrificing a few cheap ICs to the audio gods. If you have an opinion, please weigh in...