Problem with feedback/humming - Help!

[Jtrx11]

Hey all,

Been dealing with this problem and am a bit stumped for answers, hoping someone here can make a suggestion for me. Here's the story:

I recently put together a new desktop computer and installed a Creative Sound Blaster Audigy SE card. I then connected the the line in from my Sony STR-DE 197 receiver to the sound card into line in port (green).The receiver is then connected to two Cerwin Vega At-15's.

Here's the problem... After installing all of the drivers and getting the sound working, I found that when turning the receiver volume up past anywhere near half, I get a humming/buzzing noise with or without any actual audio output. I have tried messing with the computer and device volumes to find a configuration without the hum... to no avail. I then tried plugging into the onboard sound and found the same problem.

The strange thing is, I have been using this speaker/receiver setup for quite some time on my PowerBook G4 laptop (plugged directly into the headphone jack) and can turn the receiver up all of the way and get virtually no feedback.

My next step was to try using an external sound card to eliminate the buzzing on the desktop, figuring maybe there was some sort of interference caused by the proximity of the processor to the audio port and the analog signal (could this even be a problem?). I plugged my USB M-Audio Sonica Theater 7.1 sound card into the desktop and connected the receiver... same exact problem. Just to see, I then tried connecting the external sound card to the PowerBook and again found NO interference.

So it seems that the Sonica external card is clearly not the issue since it functions on the laptop. Since the built in, external, and sound blaster cards ALL get this feedback problem on the desktop, it seems like there must be some sort of problem of interference from the computer itself. Anyone had this issue or know how to solve it? Thanks!

*By the way... sorry if this was posted in the wrong part of the forum

 

[Adam]

Welcome to the forum!

That might be a ground loop issue. You can check out two articles about that here and here.

Is the desktop plugged into the same set of outlets as the receiver?

 

[Jtrx11]

Thanks Adam,

The desktop IS plugged into the same power strip as the receiver... should I try putting one on a different set of outlets? EDIT - tried plugging in a different outlet, no dice...

Based on the articles it does sound like it could be a ground loop problem. They don't give very clear instructions on how to diagnose and fix the problem though... at least for someone who isn't up with this stuff. Any guidance?

One other point I didn't mention - The humming sound is based only on receiver volume, even if the desktop system volume is at absolute zero, the loudness of the humming will change based on receiver volume setting.

 

[TLS Guy]

Thanks Adam,

The desktop IS plugged into the same power strip as the receiver... should I try putting one on a different set of outlets? EDIT - tried plugging in a different outlet, no dice...

Based on the articles it does sound like it could be a ground loop problem. They don't give very clear instructions on how to diagnose and fix the problem though... at least for someone who isn't up with this stuff. Any guidance?

One other point I didn't mention - The humming sound is based only on receiver volume, even if the desktop system volume is at absolute zero, the loudness of the humming will change based on receiver volume setting.

This is a ground loop for certain. It is caused by a potential between grounds.

I bet your laptop has a two pin plug and was likely connected to the Internet via radio.

Cable, telephone and satellite grounds are a common cause of problems.

Please do this.

Pull the Ethernet cable from you computer. If hum is still present, then disconnect the coax from any cable system, or satellite system, that may be hooked up. If the hum is still present, then for test, lift the ground from your computer, with a ground break. I bet the hum will be gone after you pull one or several of those. After that reconnect the cables one at a time and see which connection causes the ground current to flow, that is inducing the hum.

When you have that information, please report back, and I can tell you how to solve your problem.

These ground loops are common. Unfortunately people have a hard time understanding their cause and elimination.

 

[Adam]

Two things just came to mind, and it might not be a ground loop:

1. What volume do you have the computer set at? The output from your sound card is dependent on your computer volume, and if that is set really low, then your receiver is having to amplify a very weak signal - and the underlying hum might be near the level of the audio signal that you actually want. Try turning the volume on the computer up (and, consequently, the volume on the receiver down)
2. On a related note, plug a pair of headphones into that output jack on your sound card and see if you hear the hum on the headphones.

If you hear the hum on the receiver, but not on the headphones, then it's more likely that it is a ground loop.

 

[PENG]

I then connected the the line in from my Sony STR-DE 197 receiver to the sound card into line in port (green).The receiver is then connected to two Cerwin Vega At-15's.

Did you really mean you had connected the sound card's line in to the receiver's line in? I thought you are supposed to connect the sound card line out to the receiver line in.

 

[Jtrx11]

Hey guys,

Figured it out... I completely forgot to mention that I had a television connected into the receiver's video inputs - unplugging these fixed the disturbance... amateur I know. Since I never had a problem with feedback before, I didn't think that that could have had anything to do with the problem and didn't think to check. Thanks for the help guys