Optical vs. Coaxial and subwoofer hum

[habman6]

Hello,

My computer setup is simply a digital out signal from the motherboard to my receiver, and speakers. Recently my motherboard died so I had to replace it. Previously I was using an optical toslink to connect my motherboard to receiver and everything was fine and dandy. However, now my new motherboard only has a coaxial digital output, and there is a loud hum coming from the subwoofer. I have read that coaxial cables are able to transmit any sort of grounding issues whereas the optical cables do not - is this correct?

I have tried fixing the grounding issues but I keep falling up short. My next idea is to try to get an SPDIF bracket to attach to my motherboard that allows for optical out.

I just want to know if there are any other ideas before I go out and spend the money for it.

Thanks

 

[Adam]

You're correct - an optical cable with no metal will not generate a ground loop.

To help us come up with ideas, what have you tried already to get rid of the ground loop?

Here are two articles from Audioholics on ground loops, one from 2007 and another one from 2009.

 

[habman6]

You're correct - an optical cable with no metal will not generate a ground loop.

To help us come up with ideas, what have you tried already to get rid of the ground loop?

Here are two articles from Audioholics on ground loops, one from 2007 and another one from 2009.

Thanks Adam.

First I tried troubleshooting to see exactly which connections produced the hum. I managed to narrow down the coaxial connection from the motherboard to the receiver as the critical factor in producing the hum. If all components are plugged in, and the coaxial cable is not connected, then I do not get a hum. I tried using a directional cable for the subwoofer, but that did not work. I also tried different (multiple) outlet configurations to try to get the components from "fighting" for the ground.

Logically, the only thing that had changed was the optical vs. coaxial connection, which led me to believe that this may be the source.

I searched some fixes online but most involve cable tv signals (which are irrelevant in my case), or purchasing some expensive parts. I'm fairly certain it is the optical vs. coaxial issue, but I just wanted to double check

 

[markw]

Try to find a coaxial to optical converter. These should be plentiful and reasonably cheap. Hopefully, this will break the connection.

http://www.cabletrain.com/catalogsearch/result/?q=coaxial+to+optical+converter

There are others available from other sources. Google is your friend.

 

[TLS Guy]

Hello,

My computer setup is simply a digital out signal from the motherboard to my receiver, and speakers. Recently my motherboard died so I had to replace it. Previously I was using an optical toslink to connect my motherboard to receiver and everything was fine and dandy. However, now my new motherboard only has a coaxial digital output, and there is a loud hum coming from the subwoofer. I have read that coaxial cables are able to transmit any sort of grounding issues whereas the optical cables do not - is this correct?

I have tried fixing the grounding issues but I keep falling up short. My next idea is to try to get an SPDIF bracket to attach to my motherboard that allows for optical out.

I just want to know if there are any other ideas before I go out and spend the money for it.

Thanks

Lift your computer ground with a cheater plug and that will stop your hum.

 

[habman6]

Try to find a coaxial to optical converter. These should be plentiful and reasonably cheap. Hopefully, this will break the connection.

http://www.cabletrain.com/catalogsearch/result/?q=coaxial+to+optical+converter

There are others available from other sources. Google is your friend.

Thanks, that's exactly what I ended up ordering from ebay.

Lift your computer ground with a cheater plug and that will stop your hum.

I have been reading that this is not safe, and definitely not recommended. I'll try the other method first.

 

[TLS Guy]

Thanks, that's exactly what I ended up ordering from ebay.

I have been reading that this is not safe, and definitely not recommended. I'll try the other method first.

It is perfectly safe. The equipment will ground through the shield. A system must have ONE ground and one ground only, or you invite loops. I make it the practice to ground just one piece of equipment, like the preamp or power amp, and ground everything else to that. The shield of the cables is a perfectly good ground conductor, in fact they are heftier conductors than the ground wire in the mains cable.

As you know a lot of equipment does not have a three pin plug. The reason is ground loop avoidance. The gear will ground as soon as it is connected.

The larger and more complex the system, the more important it is to have one ground.

 

[habman6]

So changing the connection to an optical cable worked flawlessely. However, now I have a different problem. Every so often I'm getting a bit of white noise interference out of the left channel. Nothing about my setup has changed, so the emergence of this is quite spontaneous. Usually when I put my receiver on "direct" mode then any and all interference is lost, but this persists even then. Any ideas?

 

[TLS Guy]

So changing the connection to an optical cable worked flawlessely. However, now I have a different problem. Every so often I'm getting a bit of white noise interference out of the left channel. Nothing about my setup has changed, so the emergence of this is quite spontaneous. Usually when I put my receiver on "direct" mode then any and all interference is lost, but this persists even then. Any ideas?

Sounds as if you have a noisy IC, tramsistor or cap in the left channel that is bypassed in direct mode.