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Hum in Speakers with New Dedicated 20 amp Circuit

I just ran some 12-2 from a new 20 amp breaker and installed a dedicated outlet for my system. Now I get a very audible hum in both channels. If I switch back to the shared 15 amp outlet, no hum. I checked the new outlet with a tester and it checks out as wired correctly. At the electrical box, the black wire is connected to the breaker and the white and ground are attached to the same ground strip. I’m using a 20 amp receptacle.

Anyone with thoughts on how to resolve?

mjjw
erik_squires
15,657 posts
 

This is a sub panel.  Ground and neutral should not touch here.

mjjw OP
8 posts
 

Should the ground wire go to the block with the green screws instead of the neutral strip?

erik_squires
15,657 posts
 

OP:

The bare wire from the main panel is the ground.  It seems to be connected to the buss on the left.  The white wire from the panel appears to be connected to the bus on the right. 

Keep that separation.

Post removed 
erik_squires
15,657 posts
 

Looking at the picture, the ground and neutral from upstream were wired to the bus on the right.

If an electrician did this, get a new one.

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