PC --> Stereo Connection - Noise

I’ve been trying to connect my PC to my stereo reciever, but have been experiencing a strange noise problem. First, the details:

Motherboard - ASUS A7N8X-E Deluxe
NVidia nForce2 onboard soundcard

Denon AVR-1404

  • The noise is a constant, low humming sound.
  • The noise occurs when I use the standard stereo RCA connection (red & white), and also when I use the digital coaxial connection.
  • The cords are only 10 feet or so.
  • The noise occurs even when the receiver is set to an input channel other than that for the PC.
  • The noise occurs even when the PC and monitor are turned off!
  • I’ve tried this with two different stereo receivers, and experienced the same effect on both.
  • The noise occurs even when both devices are plugged into the same power bar (I thought it might be ground loop problem, but from what I’ve read, this should only occur if each device is plugged into a separate outlet)
  • I don’t think it’s a halt-idle problem, as the noise doesn’t change when music is playing, when the mouse is moved, or when Digital Input is turned on in the nVidia Control Panel.
  • I tried reinstalling the nVidia drivers, to no effect.
  • I tried changing various settings (e.g. muting unused inputs, etc.), to no effect.

Any suggestions?

Are you connecting to an amplified or line-level output of your computer?

Also, have you tried connecting another device to your stereo using the same cables? Say, for example, a walkman or CD player?

The first thing I would try is unplugging all the input cables from the receiver. If the hum doesn’t go away, the receiver may be picking up hum from a nearby power source. In this case, try moving the receiver. It’s also possible (but not likely) that the speaker wires are picking up hum - this would be most noticeable with very efficient speakers.

If unplugging the input cables does make the hum go away, the cables themselves could be the problem. Are they shielded? If not, replace them with shielded cables.

You say you’ve tried plugging the PC and the receiver into the same power strip. Even if you do this it’s possible to get a ground loop if one or both plugs is two-pronged. If this is the case, try reversing one plug in its socket.

In any case, from the symptoms you describe it seems very unlikely that the problem is with the PC itself. I wouldn’t look at any hardware or software settings - this would probably be a waste of time.

Try turning it down on the PC side to about 10-20% of maximal volume.

cheap cables?

We’ve got the same motherboard…what do you think of it? Mines been kinda quirky, though it could just be that I’m not really an expert in that area.

I’ll be curious how this turns out since I may want to do the same thing someday.

Thanks for the input guys,

  • I’ve tried 2 different outputs from the PC, the line out (split to stereo RCA via a splitter cable) and the S/PDIF (digital coaxial). Both of those should be line-level, right?

  • Both amps work fine with other input sources (mp3 player, CD player, etc.)

  • I haven’t totally ruled out cheap cables, but I’ve tried many different combinations of cables and the hum seems fairly consistent.

  • PC volume makes no difference.
    Further details:

  • Today there was a pulsing sound behind the hum

  • When I unplug one of the RCA jacks, the hum gets twice as loud.

I’m sure it’s the PC, but what could be causing a buzz when it’s turned off? (power supply?) I’ve got a bunch of electrical stuff in the room (TV, receiver, PS2, alarm clock, lamps, etc.), but turning the power bar off doesn’t seem to affect it.
Any more guesses?
Omniscient: It seems like a pretty cool board, though I had one other problem so far. I originally had a stick of 512MB Kingston Hyper DDR RAM (PC3200). When I first bought it, it ran wicked fast, but kept randomly hanging with no warning. Turns out it was the RAM (after months of debugging). I took it back to the store and they replaced it with a stick of PC3700, and now it runs great. Don’t know if the RAM was incompatible with the board, or maybe with the CPU (Athlon XP 3200 Barton) or video card (MSI Radeon 9800). Regardless, it works fine now, with the exception of the annoying hum.

How about magnesium? As I understand it, the buliness at either end of most computer audio cables (Headphone jacks, male at both ends) is magnesium rings. Howsabout useing such cables, or something?

It’s still worth checking out. A few years ago, I was dubbing a few LPs to WAV format. With my computer hooked up to a receiver I had that low 60 Hz hum, even though both were plugged into the same outlet strip. Connecting a wire from a case screw on the back of the computer to the ground terminal on the amp cured the problem.

I’m no expert, but if there’s hum when the connection is via digital coax I don’t see how it can be anything other than a ground loop. Interference on a digital signal won’t show up as hum the way it does on an analog signal, but rather as that kind of digital distortion warble.

Okay, so I’m starting to think maybe it’s ground loop afterall. I’m wondering if I should spring for one of these isolators on eBay - Which of would work best (if any)?

Other interesting stuff:

This site has tons of info, but nothing that really shows me what I need to buy.

This looks like the cadillac model of S/PDIF cables, but it doesn’t mention anything about ground loop.


I bought a ground loop isolator on EBay for $1.99, and it seems to eliminate 95% of the noise. They really should make these things standard on cables. Thanks for the advice folks!

I want to point out that most people dislike the frequency attentuation of a ground-loop isolator (the frequencies that are affected depend on the design of the isolator purchased). Some isolators are much worse than others. If you find after awhile that you dislike the way music sounds, I encourage you to go back and try to fix the ground loop problem. I missed this thread the first time but if you would like to keep trying, post again and I can think of a few more ways to troubleshoot this.