Subwoofer hum ground loop issue?

[suttondesign]

I recently started to notice a hum from my Rythmik E15HP subwoofer. It's not loud enough to notice while listening but loud enough to be annoying when the room is quiet.
Based on my research this is a biproduct of using a separate circuit for AV equipment and separate circuit for the subwoofer. That is the differing ground potentials may create a ground loop in an unbalanced connection. So the only solution would be to use some device to lift the ground or use a balanced connection. So perhaps an Emotiva CMX-2 might do this in a safer way which some have recommended. The subwoofer is in the back of the room my options are limited in plugging everything into a single circuit.

Anything I can do besides trying a device that was mentioned earlier? I'd like to tackle and resolve this issue.

 

[suttondesign]

I had the same problem and got the Emotiva dc offset eliminator. Completely eliminated the buzz. Totally worth it.

 

[Corock]

This looks like it has some kind of headphone jack inputs? I'm guessing there are different versions with RCA connections.

just need the right cable

 

[Lambda]

to see if it would make any difference.

Disconnect the cable and see if it helps.

 

[thepiecesfit]

I had the same problem and got the Emotiva dc offset eliminator. Completely eliminated the buzz. Totally worth it.

Is that the Emotiva CMX-2?

 

[thepiecesfit]

Hum, no pun intended, sub hum is routinely found to be caused by the Cable Box, Satellite Box. You can try to disconnect the internet lan connection from the AVR if your using this hard wire connection. It could be the cable modem?

Question. You have a cable modem but no cable tv?

Yes correct. Don't use ethernet to the AVR only WiFi for some Heos streaming. The hum disappears if I disconnect the surge protector and AV equipment in front of the room. The sub is in the back of the room on a different circuit. But frankly anything plugged back into that front wall introduces the hum again. So it doesn't seem like any one device is responsible, but rather a combination of both.

 

[thepiecesfit]

Disconnect the cable and see if it helps.

Got up on the ladder and disconnected the service into the house for coaxial for internet, did not do anything to the subwoofer hum.

 

[Lambda]

The hum disappears if I disconnect the surge protector and AV equipment in front of the room. The sub is in the back of the room on a different circuit. But frankly anything plugged back into that front wall introduces the hum again. So it doesn't seem like any one device is responsible, but rather a combination of both.

Very Methodical trouble shooting is needed.
what is the minimal setup that creates the problem? just AVR connected to the sub and power?

 

[pjug]

Surely this is a ground loop as OP suspects. Just get a cheap isolator from Amazon, BestBuy, whatever and you can confirm this. Then if you want a better one or decide to run a balanced cable, you can take it from there.

 

[raindance]

Why is it not an option run one more cable parallel to the RCA cables?


then run balanced cables aad make a "fake balanced" output by connectinon at the AVR side.
View attachment 117437

This won't fix a ground loop!

 

[raindance]

I had the same problem and got the Emotiva dc offset eliminator. Completely eliminated the buzz. Totally worth it.

Got nothing to do with a ground loop.

 

[Lambda]

This won't fix a ground loop!

what exactly and why not?

Surely this is a ground loop as OP suspects

sure it is.
But adding a transformer in the signal part is not necessarily the only solution.
And adding a transformer will defiantly affect the audio.

 

[raindance]

Doesn't matter how you fake a balanced connection with wiring, it remains single ended and the ground loop remains. You have to generate the other half of the balanced signal at the source.

 

[Lambda]

You have to generate the other half of the balanced signal at the source.

No.

if the receiver is a proper differential amplifier this is totally sufficient!

Cold = Noise
Hot = Signals + Noise

The receiver Amplifies the differential. aka Hot-Cold=signal=

(Signal + Noise)-(Noise)= Signal

 

[Speedskater]

Actually you could make a RCA to XLR adapter similar to the one in post #11 and install it at the sub-woofer end of the coax cable.
Just don't attach the shield to the RCA connector.

 

[pjug]

Actually you could make a RCA to XLR adapter similar to the one in post #11 and install it at the sub-woofer end of the coax cable.
Just don't attach the shield to the RCA connector.

I agree a pseudo-balanced solution should break the ground loop, but won't you need to wrap a shield around the cable with the XLR ground connection in a long cable run? So I can't see how this can really be a good solution with the existing coax in the wall.

 

[Speedskater]

The coax shield will remain attached at the RCA send end.
In pro XLR balanced interconnect systems, sometimes the shield is only connected at the send end.

 

[pjug]

The coax shield will remain attached at the RCA send end.
In pro XLR balanced interconnect systems, sometimes the shield is only connected at the send end.

But if you use the RCA outer conductor as part of differential input of XLR then that conductor needs shielding, no?

 

[raindance]

No.
View attachment 117462
if the receiver is a proper differential amplifier this is totally sufficient!

Cold = Noise
Hot = Signals + Noise

The receiver Amplifies the differential. aka Hot-Cold=signal=

(Signal + Noise)-(Noise)= Signal

Interesting! So what are the chances that the sub has a differential input stage?

 

[pjug]

Interesting! So what are the chances that the sub has a differential input stage?

That is a good question. Personally I would just buy the Jensen subwoofer isolation thing. Looks like it will be transparent if you look at the specs and graphs.