Pro Audio Asylum

Ground loop

99.149.122.166

In Reply to: RE: QSC hum posted by chris on June 14, 2009 at 08:09:12

You have whats called a ground loop

Easy way out........?
Yes

Get yourself a 25 cent ground lift adaptor from the hardware store
Lift the ground on one of your input units or the power amp

Lift the ground on say your pre amp first...if the hum is not
gone then try the power amp as the last unit to lift the ground
on with the adaptor

Your system will still be grounded

You are just eliminating the ground loop between your pre units
and your power amp

Follow Ups:

RE: Ground loop-DON'T DO IT!!!!!!!!!!!!!!!!!!!!!!!!!!! - Ivan Beaver 13:56:41 06/21/09 (0)
"Get yourself a 25 cent ground lift adaptor from the hardware store
Lift the ground on one of your input units or the power amp

Lift the ground on say your pre amp first...if the hum is not
gone then try the power amp as the last unit to lift the ground
on with the adaptor

Your system will still be grounded "

You should NEVER EVER lift the AC grounds!!!!!!!!! The system will NOT be grounded as the shield will not carry enough current should a problem occur.

He needs to find the REAL problem-NOT a dangerous band aid.

I suggest hooking up the balanced input to the amp as balanced and not hooking up the shiled wire.

On the preamp end hook the hot wire from the amp to the hot output of the preamp. Hook the cold wire and the shield to the ground of the preamp.

That will fix it most of the time-and he can take advantage of the commmon mode rejection of the amp balanced input.

There is not a Judge in this land who wants to hear how "the hum went away" when somebody has used a widowmaker ground lift to get rid of the noise!!!!
RE: Ground loop - chris 20:13:09 06/14/09 (1)
Thank you! But the hum (buzzing sound)comes when the interconnects are not even plugged-in the pre-amp. I thought 1st that the interconnects were faulty, so I changed them. I use interconnects that are terminated with RCAs and a RCA to 1/4 jack adaptor to fit the rmx 1450 inputs. In addition the amp is picking up other electrical devices; with the microwave on for instance, the amp starts to generate a 60 to 100 hz hum.
When I un-plug the interconnects from the amp, the speakers become dead silent. Could it be the jack? or is the amp not well designed for unbalanced inputs?
- RE: Ground loop - Pro Sound Guy 06:20:46 06/15/09 (0)
  Sounds like you have a bad interconnnect
  
  Unplug one at a time
  
  If it goes dead silent after you unplug one then you found it
  
  Otherwise try a different circuit
  
  Possible neutral/hot reverse on AC outlet?

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