Subwoofer hum ground loop issue?

[thepiecesfit]

Greetings could use some help. 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. I quickly used a ground lift adapter 3 prong to 2 as a test and the subwoofer is silent. Knowing this is not a safe solution I removed it. The AVR equipment and subwoofer are on a separate circuit. I am using an unbalanced RCA which goes to a RCA wall plate via Blue Jeans subwoofer cable and Belden RG-59 coaxial cable in wall. However, using a separate cable direct RCA end to end has the same effect. I've already tested my outlets and the polarity and ground are all correct in the house. I do not have cable tv coax but do have a cable modem in the other room.

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.

 

[pjug]

A transformer isolator will work. Some won't consider it a hifi solution, but personally I would use this if I had ground loop hum just in a subwoofer: https://www.amazon.com/GL301-Audio-RCA-Noise-Filter/dp/B00CZJYWFI

 

[thepiecesfit]

A transformer isolator will work. Some won't consider it a hifi solution, but personally I would use this if I had ground loop hum just in a subwoofer: https://www.amazon.com/GL301-Audio-RCA-Noise-Filter/dp/B00CZJYWFI

I read those line filters cause a measurable change to the frequency response. Not sure whether audible or not.

 

[pjug]

I read those line filters cause a measurable change to the frequency response. Not sure whether audible or not.

They do, but I doubt that it is a problem. That cheap one I linked says 0.5dB from 20-20000Hz. With just low frequencies probably a good deal better than this. I will search for some measurements with one of these things.

 

[pjug]

Jensen has some info: https://www.jensen-transformers.com/what-is-a-ground-loop/

I have no idea how well the cheapo device would compare to this.

 

[Corock]

This did the trick for me

 

[Speedskater]

a] Belden makes several RG-59 coax cables some are suitable for RCA analog interconnects while other's designed for cable TV are very poor choices.
b] having everything on the same AC circuit is a good plan.
c] run a heavy wire (say 10 or 12AWG) from the source chassis to the sub chassis.

 

[pjug]

Looks like BlueJeans makes one for $50 (or $100 if you need two). Probably worth the extra the money over the cheap one I linked initially:
https://www.bluejeanscable.com/articles/subwoofer-hum.htm

 

[Lambda]

No balanced input on the sub?
1.Cable TV ground loop isolator
2.Try using an extension cord for the sub and go the same way as with your RCA cables back to the AVR and plug it in the same power strip
3.use heavy gauge RCA wire.
4.Try an AC isolation transformer
5.Give up and use an audio isolation transformer

 

[thepiecesfit]

No balanced input on the sub?
1.Cable TV ground loop isolator
2.Try using an extension cord for the sub and go the same way as with your RCA cables back to the AVR and plug it in the same power strip
3.use heavy gauge RCA wire.
4.Try an AC isolation transformer
5.Give up and use an audio isolation transformer

Yes the sub has a balanced input, but the AVR/Pre-Pro does not. Running an extension cord is not an option it's almost 20 feet across the room. I suppose just a matter of finding a device that will accomplish this task without impacting the audio signal. I'll look at the previous recommendations.

 

[Lambda]

Running an extension cord is not an option it's almost 20 feet across the room.

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

Yes the sub has a balanced input,

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

 

[Andysu]

I had a hum that was appearing on my Behringer DEQ2496 that I use in the rack for my Dolby Stereo Lt Rt to boast the signal gain if I wanted to as well as using some audio limiting compression if I wanted to make the Dolby Stereo 4.2.4 matrix playback press against my body or give some extra slam or kick!
The noise I saw was like -80dB and should have been silent and so I tried some Behringer HD400 oh little coil transformers inside the box they could have made the spacing on the inputs/outputs a bit wider if I had to use different jack adaptor connector just saying. Well it reduced that signal noise down to I don't know I can't see it on the DEQ2496 it must have gone well below -100dB and that was when I did this video .... Predator on Laserdisc

 

[thepiecesfit]

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

The speaker cable, subwoofer cable run in the wall and terminated at a wall plate. I do have some Monoprice XLR to RCA cables I suppose I can try. I forgot to reply to one of your other points. Did use a Monoprice Onix RG-6 subwoofer cable to rule out anything in the wall and the hum was the same.

 

[thepiecesfit]

This did the trick for me

View attachment 117425

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

 

[Lambda]

https://www.audiosciencereview.com/forum/index.php?threads/slight-buzz-rca-to-xlr.15174/

I do have some Monoprice XLR to RCA cables I suppose I can try

I hope you understand that the cable needs to be balanced and the "adapter" needs to be at the AVR side?

 

[pjug]

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 is brilliant, except he's got coax in the wall as part of the run. But is the current setup just one mono channel over a single cable, or stereo and having the sub do the summing? If there are two coax cables in the wall then this could make a single balanced cable, if OP doesn't mind doing the summing on the preamp side.

If you just have a mono cable run then I would just get the Jensen mono device designed for low freqs:
https://www.jensen-transformers.com/product/sub-1rr/

 

[Lambda]

https://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

 

[AdamG]

Try this. Disconnect the cable tv box hdmi cord from the AVR. If this fixes the hum, and I suspect it will. You need an HDMI ground lifter.

https://www.amazon.com/Lindy-HDMI-Adapter-Female-41232/dp/B00DL48KVI

 

[thepiecesfit]

Try this. Disconnect the cable tv box hdmi cord from the AVR. If this fixes the hum, and I suspect it will. You need an HDMI ground lifter.

https://www.amazon.com/Lindy-HDMI-Adapter-Female-41232/dp/B00DL48KVI

We don't have a cable box. Though I had thought about screwing in one of those filters where the cable modem comes into the house to see if it would make any difference.

 

[AdamG]

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?