[Vince in TX]

I found a few very old threads on this topic, but nothing recent, so I’m starting one up to get some additional thoughts.

Ever since I first fired up the Servo Sub 4s, I’ve been dealing with the dreaded hum (from the drivers, not the amps).   I picked up an Emotiva CMX-6 thinking it would clean up the signal and strip the DC, but it didn’t stop the hum much to my frustration.   The problem is that the power to the subs and the power to the AVR are on separate circuits.   If I run an extension cord from the same circuit as the AVR, the hum is gone.   I can only conclude that there’s a ground loop issue.

Short of having an electrician rewire one of the plugs at the front of the room, tying it to the same circuit as the AVR, what other options are there?   Thanks.

[mlundy57]

Try connecting a ground wire from the chassis of the sub amp to the chassis of the AVR

[Vince in TX]

Try connecting a ground wire from the chassis of the sub amp to the chassis of the AVR

The AVR and the subs are about 20-25 feet apart.    That would be a very long ground wire.   😊   When I disconnect the RCA lines, the hum is also gone.   I suspect the root of the issue is the difference in the ground from the wall and the ground from the AVR feeding through the RCA interconnects.

But something else just dawned on me.   I found an article on audioholics talking about this very issue, and it mentioned dimmers or smart plugs.   Well, when I built the riser platform, I tied it into the same circuit where the subs are now connected.   The riser not only supplies power to the seats, but it also has a smart dimmer for the safety lighting.   I would wager this is the source of the problem.

So, I just ordered a 25’ 14/3 black extension cord as a temporary solution.

[mlundy57]

The AVR and the subs are about 20-25 feet apart.    That would be a very long ground wire.   😊   When I disconnect the RCA lines, the hum is also gone.   I suspect the root of the issue is the difference in the ground from the wall and the ground from the AVR feeding through the RCA interconnects.

But something else just dawned on me.   I found an article on audioholics talking about this very issue, and it mentioned dimmers or smart plugs.   Well, when I built the riser platform, I tied it into the same circuit where the subs are now connected.   The riser not only supplies power to the seats, but it also has a smart dimmer for the safety lighting.   I would wager this is the source of the problem.

So, I just ordered a 25’ 14/3 black extension cord as a temporary solution.

I hear you. My sub amps are 25' from the preamp which is connected to the AV processor. I had lots of hum issues when using RCA interconnects. I switched to balanced interconnects and that solved the problem. A rather expensive fix though because I had to replace my A370PEQ3 amps with A370XLR3 amps to get balanced inputs for the subs.

Your extension cord fix is a lot less expensive. 

[DigIndig]

I would suggest an additional troubleshooting step to eliminate all possibilities: connect the AVR with an extension cord to the same circuit as the sub amp. If the hum goes away, then it is indeed bias between the circuits. If the hum remains, then it's possibly being introduced by something else on the circuit, like the seats, which might suggest a different, easier fix.

If you're looking for more, I'd consider some of the options listed here: https://www.techhive.com/article/3063590/how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems.html

[Vince in TX]

I would suggest an additional troubleshooting step to eliminate all possibilities: connect the AVR with an extension cord to the same circuit as the sub amp. If the hum goes away, then it is indeed bias between the circuits. If the hum remains, then it's possibly being introduced by something else on the circuit, like the seats, which might suggest a different, easier fix.

If you're looking for more, I'd consider some of the options listed here: https://www.techhive.com/article/3063590/how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems.html

That’s actually a good idea.  Thanks for that.   I’ll try it.