[PLUG] Ground Loops / Hum

[Casey Bralla via plug <plug@lists.phillylinux.org>]

I've got some significant hum in my audio distribution system due to 
ground loops and would appreciate some electrical engineering 
suggestions on how to fix.

My basement computer runs Music Player Daemon (MPD) and feeds the analog 
audio output into a distribution point that connects to multiple stereo 
amplifiers in various rooms of the house.  I've run shielded audio cable 
in the walls and terminated them with standard RCA plugs at each end.  
Since the house was already finished, I had to run wires where it was 
possible, not always avoiding power lines.

NOTE: I don't want to use digital audio due to variable latency in the 
reproduction.  Right now I can walk from room-to-room, and the audio is 
all perfectly synchronized.

Currently, I have all the signal lines tied together, and all the ground 
lines tied together.  This, of course, is considered bad practice 
because it allows for ground loops.  (Although I've done it previously, 
and never had a problem [sigh])  .

So how should I kill the ground loop?

I tried enhancing the earth ground connection to the shielding, but this 
didn't help.

One thought I had was to separate all the grounds at the distribution 
box.  Each cable run to the distribution box would be grounded only to 
its individual amplifier.  This means the signal lines will still be 
shielded, but will be floating relative to ground.  Is this acceptable 
practice?

Your suggestions would be appreciated.

TIA!

Casey


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