2. amps-preamps
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Ground loop feedback - cable wire issue

After installing an amp there was a ground feedback low hum noise. Muting ht system made it go away but not a good solution. Also, routed cable thru surge protector and this substantially reduced problem, but still slightly there. I don’t like using surge protector.

cable co came and grounded cable wire. But this did not solve problem and I still need Cable wire to go thru surge protector. Outlets in room all controlled by one circuit. All components except tv and amp share a surge protector. Tv goes thru power conditioner and amp plugged directly to wall.

disconnecting cable wire eliminates feedback noise, even after being grounded.

Seems amp related, not sure why.



emergingsoul
saika2
31 posts
 
An unusual trick that can work wonders is to flip the AC supply polarity of the offending device, in this case the preamplifier. Chassis to ground potential difference due to internal transformer current leakage can alter considerably with changing AC supply polarity and can potentially reduce hum/noise.

One can also measure this with a multimeter to determine the optimal polarity.
atmasphere's avatar
atmasphere
11,803 posts
 
An unusual trick that can work wonders is to flip the AC supply polarity of the offending device, in this case the preamplifier.
You can only do this if the preamp employs a 2-prong AC connection!


Ground loops occur when different parts of the system share a ground in such a way that noise in the ground is imposed into the signal at an earlier part of the circuit. The best way to eliminate it is to break the common ground- usually at the amplifier end as this is where most of the current usually is. If you can float the amplifier's AC ground at the power cord (using a ground cheater available from a hardware store) and that eliminates the buzz, then there are steps you can take to shut things up.
emergingsoul OP
1,135 posts
 
 the marantz avr I have lacks a third prong vs the external amp which has a third prong.  Why is this?
atmasphere's avatar
atmasphere
11,803 posts
 
The Marantz must be an older unit. All consumer electronics are required to have a grounding pin in their AC cord **unless** there is no metal of the product exposed to the outside world. 
ditusa's avatar
ditusa
1,883 posts
 
@ atmasphere, My emotiva xpa 1 gen-2 amp is a two pin ac cord. That is four years old. Do you think, i will have a problem. Mike. :-)
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