Humming sound from speakers when connecting via Coax

[engelkie]

Here is my setup:

Product & firmware version: Mede8er MED500X f/w v1.2.2
Audio: Coax output > Logitech Z5500
Audio setting: SPDIF Passthrough / Night mode OFF
Video: HDMI output > Samsung 50" Plasma
Video setting: 720p 60Hz,16:9
Media Source: Internal HD


Whenever I connect my Logitech Z5500 to the Mede8er via coax, the subwoofer starts humming. It is quite loud. Seems there is some feedback coming from the Mede8er? Maybe the transformer used in the power adapter?

Any help would be appreciated, because my Xbox is connected via optical to the Z5500, otherwise I would have gone the optical route.

[Insomniac]

I have my coax running to the digital input of my A/V receiver and I get no feedback whatsoever.

Is there any difference if you remove the optical cable or is the feedback still there?

Have you tried another coax cable?

Is it a good quality audio cable or are you using one of the thin cables from the RCA stereo cable set?

Is the feedback a constant hum or only during certain operations / movies? If only during movies, what audio channels are included in the respective problematic containers?

Is the hum still prevalent if you connect the optical cable (for trouble-shooting purposes)?

Is there any other electrical cable running in parallel with the coax audio cable?

[engelkie]

Thank you for the response. Here are my answers to your questions:

Is there any difference if you remove the optical cable or is the feedback still there?
Feedback is still there.

Have you tried another coax cable?
Yes

Is it a good quality audio cable or are you using one of the thin cables from the RCA stereo cable set?
It came with the speaker set. It is quite thick and is gold-plated.

Is the feedback a constant hum or only during certain operations / movies? If only during movies, what audio channels are included in the respective problematic containers?
It is a constant hum. As soon as the coax makes contact with the Mede8er it starts humming, even during the Mede8er's boot sequence. If I plug the cable out or power down the Mede8er the humming stops.

Is the hum still prevalent if you connect the optical cable (for trouble-shooting purposes)?
With the optical cable there is no humming and the sound is beautiful.

Is there any other electrical cable running in parallel with the coax audio cable?
No. The Z5500 has a connection console that is standing close to the Mede8er.

[ricardo]

just a quick one

If you physically move your mede8er away from everything does the humming change in pitch or reduce or does it stay the same

Cheers

[Insomniac]

- is there a power line running in parallel with the console wiring back to the speaker's amplifier (sub)?

[engelkie]

@ricardo - Moved it around a bit, but didn't have an effect.

@insomniac - No, they go separate ways.


Also noticed that the humming has a beat to it... At 1 second intervals, the humming gets a bit louder for a split second. It's like someone banging a drum.

I now went as far as unplugging all the other electrical equipment and leaving the Mede8er and the Z5500 plugged in on the same wall socket... But it still hums 

Looks to me like I'll have to revert to the optical connection and then let the XBox output via the TV speakers.

[ricardo]

@ricardo - Moved it around a bit, but didn't have an effect.

@insomniac - No, they go separate ways.


Also noticed that the humming has a beat to it... At 1 second intervals, the humming gets a bit louder for a split second. It's like someone banging a drum.

I now went as far as unplugging all the other electrical equipment and leaving the Mede8er and the Z5500 plugged in on the same wall socket... But it still hums 


Looks to me like I'll have to revert to the optical connection and then let the XBox output via the TV speakers.

Looks like the interference  is coming from the mede8er.

It could be a faulty circuit its funny that it does not come though the optical cable it could be something on the Coax output.

If I was you I would take it back and get a new one your unit might be faulty.

Cheers

[engelkie]

Looks like the interference  is coming from the mede8er.

It could be a faulty circuit its funny that it does not come though the optical cable it could be something on the Coax output.

If I was you I would take it back and get a new one your unit might be faulty.

Cheers

I think it is the Mede8er's power pack. It is a step-down transformer, thus it can cause the noise on the electrical circuit. But that does not mean it is faulty.

The optical doesn't generate the noise, because the optical cable doesn't conduct electricity. When the coax is connected, it completes a ground loop, thus the sub picks up the noise.

I'll see if I can find a ferrite choke to insert between the power pack and the Mede8er... Anyone know where I can buy some?

[engelkie]

I solved it!

Thanks everyone for your help!