Hello,

I would like to add my "experience" with hum. I just received Model 990/7500 combo. And right of the bat, I was greeted by the hum. I pretty much disconnected everything and rearranged the power cables with no reduction of hum. I finally put everything back together and started all over again. During this exercise I noticed few things:
- I was able to "effect" the hum level while playing behind the rack (high, low, etc.)
- The hum was there when the RCA cable was connected between 990/7500 (attached on both ends).
- The hum was there when the RCA cable was only attached to 7500 but not to the 990.
- The hum was gone once I disconnected the RCA from 7500.
- I thought the cable was acting somewhat like an antenna.
- The hum was not there when I used my old Rotel Ampplifier (stereo) using the same cable.
- I changed the RCA cable with a Monster Cable ULT-I600, 4feet, the hum went away. Nada, zilch, zero.
- I will be bringing home some instrument tonight to see if I could measure any interference coming out of 7500 when compared to Rotel.
- Rotel is "power consumption" rated at 400 Watts vs. the mighty 1800 Watts of 7500. Though, I do not know if this should make any difference.

I will let you know if I have the right instrument (Tesla?, Gauss?, I am very poor in electromagnetics...) and the results of my measurements.

Cheers,

H2O