Ground loop hum...help me further narrow down the fix - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 18 Old 03-23-2020, 01:01 PM - Thread Starter
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Ground loop hum...help me further narrow down the fix

I relocated my equipment rack to a better location and multiple circuits to handle multiple amps and future growth. I went from two 15 amp circuits to three 20 amp circuits. Previously I had a ground loop hum that was fixed by grounding all the amps to each other. Now this fix no longer solves the issue.

THE CABLE COAX HAS BEEN RULED OUT. I removed the cable and the box and the hum remained. It is a matter of the amps being on multiple circuits. Amps are an nu3000 & an nu6000 for subs, and a Crown XLI 2500for R/L mains. The noise is in the subs and the fronts.

I have determined that circuit 3 is "noisier" than 1 & 2 by process of elimination by leaving each circuit out of the mix one at a time. Circuit three has many issues as I followed the wiring but I'm not sure which one to go after first. Here are the issues:

1. I can't fix this one, but this circuit snakes from one upstairs outlet to the downstairs washer/dryer, to outside outlets, and goes underground to power an outside barn/shed.
2. All outlets have been checked for polarity. One is reversed but it's not being used and nothing is plugged into it. Can that still cause issues?
3. Two fluorescent lights are part of the circuit, but they are turned off. Can this be the issue even though they are turned off?
4. One of the outside outlets is a GFCI. I don't even know if this is up to code because it's not even covered. Eventually I'll replace it with a normal covered outlet. Can a GFCI outlet just being on the circuit be the issue?
5. All outlets are old (50 years+) but functioning. Ultimately I'll replace all for safety's sake.

So there it is TLDR assume not cable/coax related ground loop...can unused GFCI in circuit, unused florescent lights in circuit, unused reversed polarity outlet in circuit cause the ground loop?

Thanks for reading and those who respond.

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post #2 of 18 Old 03-23-2020, 01:20 PM
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Take a read
https://www.avsforum.com/forum/155-d...l#post59153882

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I had the same type of issue and never was able to figure it out. My house was built in 1950 and when I we purchased the place 4 years ago the panel had been upgraded to 200 amp service. The circuit I run the inuke 3000 and parasound amp was on a 20amp breaker but lights and a gfi switch came before the outlet I was using. I ended up running a dedicated 20amp line and new outlet and the issue completely resolved. A friend of mine thinks it was the 2 T8 lamps that were on that circuit saying the ballasts could have caused the hum, I guess I will never know.

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post #4 of 18 Old 03-23-2020, 02:04 PM
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Originally Posted by Krbass View Post
I had the same type of issue and never was able to figure it out. My house was built in 1950 and when I we purchased the place 4 years ago the panel had been upgraded to 200 amp service. The circuit I run the inuke 3000 and parasound amp was on a 20amp breaker but lights and a gfi switch came before the outlet I was using. I ended up running a dedicated 20amp line and new outlet and the issue completely resolved. A friend of mine thinks it was the 2 T8 lamps that were on that circuit saying the ballasts could have caused the hum, I guess I will never know.

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Do you have balanced to RCA cables in between your AVR and amp? If so, take a look at the thread I linked to in post #2

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post #5 of 18 Old 03-23-2020, 02:06 PM
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Just for a trial experiment, plug everything into the same outlet with a power strip. If the hum remains, try It in different outlets on different circuits. See what happens. If it’s gone that will tell you it’s the multiple outlets causing it.
Also, do you have the amps grounded to the AVR? That solved most of my hum when I had Inukes.
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post #6 of 18 Old 03-23-2020, 02:26 PM
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Quote:
Originally Posted by johnson636 View Post
Do you have balanced to RCA cables in between your AVR and amp? If so, take a look at the thread I linked to in post #2
I have the monoprice cables, I never thought that would have been the issue

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post #7 of 18 Old 03-23-2020, 02:39 PM
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I have the monoprice cables, I never thought that would have been the issue

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Yup, so do I. I just haven't addressed the issue yet.

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post #8 of 18 Old 03-23-2020, 02:53 PM
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I had that issue too.
All my circuits were next to each other but in separate boxes so I tied all the commons (Uncoated wire) together from box to box and this fix my issue.
I also ran a ground from amp to amp INCLUDING my minidsp2x4 which helped.
One other noise problem I had was keeping my usb cord plugged into my computer from my minidsp. As soon as I unplugged the usb from the computer it would go away. I later grounded my computer and my minidsp to my amps and that fixed that.
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post #9 of 18 Old 03-23-2020, 03:38 PM - Thread Starter
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Quote:
Originally Posted by johnson636 View Post

Did that a long time ago. Did not change anything.

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post #10 of 18 Old 03-23-2020, 03:45 PM - Thread Starter
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Quote:
Originally Posted by Jk7.2 View Post
Just for a trial experiment, plug everything into the same outlet with a power strip. If the hum remains, try It in different outlets on different circuits. See what happens. If it’s gone that will tell you it’s the multiple outlets causing it.
Also, do you have the amps grounded to the AVR? That solved most of my hum when I had Inukes.

Everything was chassis grounded/daisy-chained together and that solved the old hum issue. Now with three circuits it doesn't fix the issue. Circuit 3 (like I described above) is the big noise/hum issue and I listed all of the problems I found and will eventually fix, but being in this Corona Virus situation running to Home Depot and buying this and that is not as easy now. I'd like to see which issues on circuit 3 are the most likely culprit.

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post #11 of 18 Old 03-23-2020, 05:45 PM - Thread Starter
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Quote:
Originally Posted by Jk7.2 View Post
Just for a trial experiment, plug everything into the same outlet with a power strip. If the hum remains, try It in different outlets on different circuits. See what happens. If it’s gone that will tell you it’s the multiple outlets causing it.
Also, do you have the amps grounded to the AVR? That solved most of my hum when I had Inukes.
I just did exactly that. Results with mic right up to the speaker.

Circuit 1: buzz/hum is 29db (cannot really hear it from seating position)
Circuit 2: buzz/hum is 36db (can hear it from seating position, but bearable)
Circuit 3: buzz/hum is 51db and can be heard outside of the theater

Circuit 3 again is the main culprit and I'm going to start fixing things on my list in the next couple of days. All I really need to buy is an outlet cover to replace that outside GFCI outlet which is for some reason not covered.

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post #12 of 18 Old 03-24-2020, 04:51 PM - Thread Starter
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For anyone that encounters a similar situation I'll keep updating this thread with results until I give up. Again, this circuit is the "noisy/humming" one and it snakes from upstairs to downstairs to the outside outlets and finally underground to the shed/barn. Outlets and wiring are decades old.

The results of first replacing the outside GFCI were promising. I went with a regular 20 amp outlet and cover. After doing just that I remeasured the hum again and it was around 30db but still noticeable. It's possible the ground was not making good contact because when I pulled the old outlet out the ground was not attached.




Then I replaced the reversed wired outlet. I think the ground had lost contact over the years in this one. For some reason replacing the outlet and properly wiring it increased the hum to around 36db (measured right up on the speaker.)






I still have about 8 outlets to replace in the shed/barn. But there was some progress made today.
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post #13 of 18 Old 03-24-2020, 04:59 PM
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Originally Posted by DaleNixon View Post
For anyone that encounters a similar situation I'll keep updating this thread with results until I give up. Again, this circuit is the "noisy/humming" one and it snakes from upstairs to downstairs to the outside outlets and finally underground to the shed/barn. Outlets and wiring are decades old.

The results of first replacing the outside GFCI were promising. I went with a regular 20 amp outlet and cover. After doing just that I remeasured the hum again and it was around 30db but still noticeable. It's possible the ground was not making good contact because when I pulled the old outlet out the ground was not attached.




Then I replaced the reversed wired outlet. I think the ground had lost contact over the years in this one. For some reason replacing the outlet and properly wiring it increased the hum to around 36db (measured right up on the speaker.)






I still have about 8 outlets to replace in the shed/barn. But there was some progress made today.
I had a groundloop hum caused by the 3.5mm jack on my receiver. Try disconnecting the 3.5mm trigger cables connected to your amps.
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post #14 of 18 Old 03-24-2020, 05:03 PM
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You have an old house?

Make sure you HOUSE is grounded.

Outside by your power meter you should have a large 8ft long x 3/4 inch round copper ground rod going into the ground and a wire going to your power meter / fuse box to ground your house. Not many houses are not grounded but the ones that are not grounded have nightmare problems.
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post #15 of 18 Old 03-24-2020, 05:15 PM - Thread Starter
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Originally Posted by Audiophile75 View Post
You have an old house?

Make sure you HOUSE is grounded.

Outside by your power meter you should have a large 8ft long x 3/4 inch round copper ground rod going into the ground and a wire going to your power meter / fuse box to ground your house. Not many houses are not grounded but the ones that are not grounded have nightmare problems.
I think it was built in 1963. Looks like it's not grounded the way you describe. The other two circuit's I'm using are not bad at all; the humming came by adding this convoluted circuit.


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post #16 of 18 Old 03-24-2020, 05:35 PM
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Thumbs up

Great you managed to fix the issue. I gave up and ordered Jensen transformer to resolve the issue.
https://w ww.jensen-transformers.com/product/sub-2rr/

what-i-d-do-differently-next-timehttps://www.avsforum.com/forum/19-ded...l#post55641388
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post #17 of 18 Old 03-24-2020, 05:59 PM - Thread Starter
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Great you managed to fix the issue. I gave up and ordered Jensen transformer to resolve the issue.
https://w ww.jensen-transformers.com/product/sub-2rr/

Sort of. The first fix improved it and the second one made it a little worse.

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post #18 of 18 Old 03-25-2020, 03:48 PM - Thread Starter
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Instead of replacing each of the barn/shed outlets I simply disconnected the wiring so the circuit ended before going underground & reaching the barn. There was no improvement. The only thing that made a significant improvement was replacing that old outside GFCI outlet which may have lost contact with the ground and/or the ground wire was touching the metal box in which it was enclosed.


With two quiet 20 amp circuits I still have enough power easily for now. When I add the NX6000 I'll probably tap into a different circuit for it.

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