Loud hum from subwoofer

[mmaatt747]

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.

Does anyone have any suggestions?

 

[VincentP]

Do you hear the hum without any audio input connected to the speakers?
Does it persist while playing audio?
Is the power input filtered?
Is the power input earthed?

Depending on which country you are in, mains is usually 50 Hz or 60 Hz. These frequencies are in the range of the sub so any interference from mains will produce an audible hum.

 

[mmaatt747]

Thanks for the reply. I'm in USA and it does persist while playing audio. If it helps, the hum immediately goes away when I disconnect the cord from the Ceres speakers. And while it is still connected to the sub, if i touch the end of the cable the sound comes right back.

I doubt the power input is filtered since I'm only using a standard surge suppressor. Also, both power cords for the Ceres speakers and the sub only have 2 prongs... no 3rd prong for grounding (which seems crazy to me)

 

[jsmithepa]

Try no surge suppressor. Reverse one or both of the plugs (unplug, turn 180, re-plug) if able. Got a plain power strip? try that, plug both into the same power strip. Do you know how to test for wall plugs proper ground wiring?

If none of these work, is not unheard of faulty electronics (Ceres).

 

[americanaudiophile]

There may be a ground loop because the AC grounds are connected together. Try a 3 to2 ground lifter on the sub power cord. You can also try an audio ground isolator on the audio input of the subwoofer.

 

[mmaatt747]

Try no surge suppressor. Reverse one or both of the plugs (unplug, turn 180, re-plug) if able. Got a plain power strip? try that, plug both into the same power strip. Do you know how to test for wall plugs proper ground wiring?

If none of these work, is not unheard of faulty electronics (Ceres).

Thanks for the reply.

I tried with no surge suppressor and got same hum. I did try a different outlet in my house and it improved a little. Also, reversing the one plug that I could (Ceres speakers) improved it a little as well. But unforatunately there is still way too much hum.

Another thing I just noticed is that if I touch any metal screws or other ports on the Ceres speakers, it greatly increases the hum from the sub.

I'm thinking maybe I don't have good ground wiring in my house? I'll do some searching online.

 

[mmaatt747]

There may be a ground loop because the AC grounds are connected together. Try a 3 to2 ground lifter on the sub power cord. You can also try an audio ground isolator on the audio input of the subwoofer.

Thanks for the reply. I'm going to look into the ground lifter and audio ground isolator now.

Another thing I just noticed is that if I touch any metal screws or other ports on the Ceres speakers, it greatly increases the hum from the sub.

 

[mmaatt747]

There may be a ground loop because the AC grounds are connected together. Try a 3 to2 ground lifter on the sub power cord. You can also try an audio ground isolator on the audio input of the subwoofer.

I just ordered this isolator.