It sure is a mystery.
when running 990/7700 unbalanced I had a noticeable hum. Running balanced...no hum.

Here's something that doesn't make sense to me...and maybe gonk can explain: When runnign the 990 and all the same equipment in the same installation...with the only thing different being my 755 (which is unbalanced) there was NO HUM.

Don't understand.
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Living Room:
5.1 Surround and 4channel inline room
990/7700/6-KEF-107s/LFM1 x 2/ SMS Awaiting Trinnov
Millenium dts decoder;Digital Director
Players: Tascam CD01U/SonyCX455 x 3/DV955/BDP83
Old Sony 60" SXRD TV
Zone 2 (also liv-Room: listening to music while Mrs watches TV): Crown SL2 preamp/D40 Amp/Stax Headphones



My "Man-cave":
4 channel-only inline room. No TV (thank heaven)!!!
990/755/4-KEF 107s
Tascam CD01U/dts decoder/digital director
Alesis 16x4x2 mixer
Recorders Alesis HD24/ML9600/Crown CX844s/SonyDAT/Tascam DA38
Ham Radio Shack (KB1STH) ICOM/Yaesu/Drakes x 3