Hum from PC to PrePro - Ground problem?

[adk highlander]

I have my computer tied into my prepro to play internet radio and iTunes. The computer is about 50ft away and I have a long RCA cable that runs the distance. I am using this instead of digital because my prepro will only uses analog sources for the 2nd and 3rd zones. For some reason there is a major hum now. (This is a new computer) If I plug my iPod or another source into the cable there is no hum so it must be from the computer. Is there a way to ground the pc or does anyone have another suggestion?

thanks.

 

[mtrycrafts]

... If I plug my iPod or another source into the cable there is no hum so it must be from the computer. thanks.

What kind of cable is that 50footer? Perhaps it is picking up something?
What do you mean by the above? Meaning that you unplug the computer and plug in the ipod to that 50ft cable?
Your computer has a 3 prong cord on it, right?
You may try an experiment by using an extension cord on the computer power and run it to an outlet by the audio gear/processor and see if it still hums.

 

[TLS Guy]

Ground loop

You have a ground loop. This occurs when there is a small voltage between grounds. Try and use the same electric power point for both systems. This may no solve it. Computers are notorious for ground loop problems. If the above does not work, then try a ground break on one of the systems to test it. This is not the safest long term fix, bit if it works you have proved it is a ground loop. The safest permanent solution is an isolating transformer.

Take a look at this pdf.

http://www.cinemasource.com/articles/gnd_loop.pdf

 

[adk highlander]

Thanks guys.

The 50ft is a spliced AR and radioshack cable.

mtrycrafts, I did mean that if I plug other sources (the iPod or portable CD player) into the cable I do not get the hum from that cable. It does have a 3 prong and I will try other outlets to see if that makes any difference.

TLS, thanks I will take a look at the article. This did not happen when I was using this computer in the theater and only now is happening after moving it to my office.

 

[TLS Guy]

Different grounds

The whole clue here is that you moved the equipment and are using different grounds. Trust me there is a potential between the grounds of your current set up. That is the cause of your hum.

 

[mtrycrafts]

Thanks guys.

The 50ft is a spliced AR and radioshack cable.

mtrycrafts, I did mean that if I plug other sources (the iPod or portable CD player) into the cable I do not get the hum from that cable. It does have a 3 prong and I will try other outlets to see if that makes any difference.

TLS, thanks I will take a look at the article. This did not happen when I was using this computer in the theater and only now is happening after moving it to my office.

That eliminates a cable issue of that long length and is the computer and a different circuit outlet. Hopefully that extension cord experiment will shed some good light on this.

 

[adk highlander]

I solved this issue after buying a ground loop isolator. I was about to buy one from Impact Acoustics for 80 bucks but found one for just 6 that offered the same specs. Well not having a ton of case right now I went with the 6 dollar one and it worked like a charm.

Joe Cornwall posted this article recently about connecting your PC and HT and he covers these devices in the article. Just wanted to let people know that there are cheaper alternatives and they do work. http://www.audioholics.com/tweaks/connecting-your-system/connecting-home-office-theater

The one I bought was from raptor.