Since we are on the topic...
What level of hum is considered a real ground loop problem? Since I've introduced a separate amp (Newcastle AM-9080) I've noticed a hum at the speakers that wasn't there before when just using my AVR (Onkyo 806). I tore my system apart to isolate the issue last night and traced it back to a few sources.
1. Coax digital input from HTPC to AVR (now acting as a pre/pro).
2. HDMI input from HTPC to AVR (yes, there is a common well-known theme here baout PCs and EMI/RFI)
3. HDMI input from TivoHD DVR.
4. HDMI output to TV/Projector
Now, the hum is really low. You can only hear it if you are within about 6" of the speakers (M60s). When I remove the HTPC connections and the coax from the DVR the noise level drops to almost imperceptible but barely there. I've already ordered a Cable ground loop isolator, and will replace the coax digital from the HTPC with an optical connection, but there really isn't that much I can do about the remaining HDMI connections.
So, what is considered a ground loop problem? A loud (audible from a distance >1 ft.) hum or any hum at all?
It definitely isn't the amp. I tested the noise floor by hooking up an iPod directly to the inputs as well as the AVR with a single optical input connection then standard interconnects to the amp and both test show zero noise...
Thoughts?
