Loud hum from subwoofer

[mzattage]

I purchased these Ceres C4.5Bt speakers:



http://www.newegg.com/Product/Product.aspx?Item=9SIA18T3MJ5032&cm_re=ceres-_-9SIA18T3MJ5032-_-Product



I connected a powered subwoofer to the Sub Out port on the back of these speakers. But I get a REALLY loud hum from the sub. I thought it might be the sub so I tried another powered subwoofer and it does the same. The Sub Out port is a 1/4 stereo jack port. So I'm using the adapter that came with it that changes it from a 1/4 in. headphone jack to RCA and using an RCA cable to connect them to my subwoofer.



I read on their troubleshooting guide that a hum can be cause by a ground loop and that you should connect the power of the sub to the same power as the speakers. But they are so that is not the issue. I'm using a short RCA cable that is not running near any power cables so that's not the issue either.

If it helps, the sound immediately goes away when I unplug the cable including the adapter from the sub out port. Then if I touch the end of the adapter with my finger while it's still connected to the sub, I get the same hum.

Does anyone have any suggestions?

 

[WaynePflughaupt]

The Sub Out port is a 1/4 stereo jack port.

No, the sub output is a mono (T/S) jack not stereo. You should be using a cable like this (assuming your sub has RCA inputs).

​

Regards,
Wayne A. Pflughaupt

 

[mzattage]

Oh interesting I did not realize that. However I am actually using the adapter that came with the Ceres speakers. It's this one.

So I am using a single RCA cable with two male ends. One end to the subwoofer and the other end into this adapter.

Before I saw your response I actually tried using another adapter. It was the same as above but instead of converting to RCA it converts to standard 3.5mm stereo.

Then from this stereo adapter I used a normal stereo RCA cable (red/white) and ran it to the Line In (Filtered) RCA jacks on the sub (whereas with the other cable it ran to the single RCA unfiltered input).

This got rid of the hum... but now the sound is VERY quiet. Maybe because as you said it is a mono OUT on the Ceres speakers

 

[theJman]

Another thing you could try is to use the original adapter and cable, then put one of these on the subwoofer power plug. Sometimes that will eliminate a subwoofer hum associated to a ground loop.

 

[mzattage]

Another thing you could try is to use the original adapter and cable, then put one of these on the subwoofer power plug. Sometimes that will eliminate a subwoofer hum associated to a ground loop.

Thanks Jim. I should have mentioned both the Ceres speakers and the powered sub have 2 prong plugs. I have ordered this isolator hoping that might solve the issue.

https://www.computercablestore.com/analog-and-digital-ground-isolation-transformer-rca-mf-3

 

[theJman]

Be sure to come back and let us know if it solves the problem. I'm curious to find out how that device works in a situation like yours.

 

[mzattage]

Be sure to come back and let us know if it solves the problem. I'm curious to find out how that device works in a situation like yours.

Yeah will do. Based on the package tracking it should arrive on 12/22.

 

[mzattage]

Be sure to come back and let us know if it solves the problem. I'm curious to find out how that device works in a situation like yours.

Well no luck... the sub gets no signal at all with the isolator.

 

[theJman]

Look on the bright side; the hum is gone at least...

Is it possible that one's a DOA? Not getting any signal suggests that may be the case.

 

[mzattage]

Look on the bright side; the hum is gone at least...

Is it possible that one's a DOA? Not getting any signal suggests that may be the case.

haha that was my thought when I first plugged connected the isolator! No hum yay!! Then I quickly realized it was isolating ALL sound. Anyway they are shipping me a replacement today. I will update once I receive it.