Wayne Parham Messages: 18791 Registered: January 2001
Illuminati (33rd Degree)
Looks like a really nice system!
Hum cannot be caused by a passive loudspeaker. It's usually power supply noise but nearly as often, it's a ground loop. Sometimes it's induced AC line noise, usually the result of a lifted ground.
Do you have sound from cable TV connected to the system? If so, be sure to isolate the video system using a matching transformer on the cable line input. They're really designed to connect 75Ω coax to 300Ω balanced inputs and vice-versa. But you can run two of them back to back so they run 75Ω->300Ω->75Ω to isolate the ground. The reason this is important is the ground run on cable TV systems is usually at a slightly different potential that local earth ground. That's the definition of a ground loop, and it's exceedingly common.
There are other ways to create a ground loop too. Even having some devices connected to AC on one wall and other devices connected to sockets on another wall can sometimes create a ground loop. If the ground connection on one leg is sufficiently far from the connection on the other wall - if the wire in the wall is long enough - then there can be a slight difference in potential, and that's what causes a ground loop. The symptom of this condition is hum.
So start disconnecting stuff and see if you can isolate the noisy device and/or connection. Once you've found the culprit, you can further evaluate whether it is caused by a ground loop, power supply ripple or induced noise and solve the problem accordingly.
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