Need help eliminating audio hum on htpc/receiver

[HeXploiT]

I'm running an htpc with a sb audigy out(old analog to rca inputs on receiver) through a home audio receiver to my home speakers and I'm getting a lot of hum. I plugged the pc and amp into the same outlet which didn't help any. I then ran a ground directly from the wall outlet to the receiver/amp casing which cut out half the hum but there's still too much hum and it's annoying to the point that it gives me a headache. I thought that a ground to the amp would fix this but apparently not. It is a small ground wire though...would a larger gauge wire help?
Anything else I can do to eliminate the noise?

Btw I have disabled the mic under Vista but it made no difference.

 

[Modelworks]

Start by disconnecting everything from the receiver except the speakers. Connect only the pc to it and see if the hum is still there. If it is then I would get a voltmeter and set it to AC. Place one probe on the pc case and the other on the ground connection of the outlet , there should be little difference, 10mv or so. If that is ok, then put one probe on the pc case and the other on the receiver case. Again there should be no voltage showing . Next measure between the outside of the rca inputs on the receiver to the pc case . If all of that shows no voltage then I am stumped because that pretty much covers all the ground points.

Normally on a receiver the amp is isolated from the wall AC by a transformer. Some of the newer receivers don't do that and use switch mode power which can lead to ground loops. The reason you measure the outside of the rca jacks on the receiver is because some amps have those at a different ground potential than the receiver case to prevent noise.

If the receiver has a powered sub, disconnect that also for the test. You want the only thing plugged in on the receiver side to be the amp itself.
If that solves the problem then start reconnecting things to the receiver till you find the culprit.


If you don't own a voltmeter you can pick one up really cheap for under $15. It just needs to read AC and DC , nothing fancy.


If none of that works you can use a car audio ground loop isolator, but they can change the clarity of the sound. http://www.radioshack.com/prod....jsp?productId=2062214

 

[HeXploiT]

Alright thanks for taking to time to post that Modelworks. I'll pick up a voltmeter when I get the chance this week and follow your steps.:thumbsup:

 

[Noubourne]

Most likely, you just need to unplug your cable/sat from the wall, and the hum will stop. By far the most frequent cause is improperly grounded cable/sat wiring. Lots of cable guys ground it somewhere other than where all your power is grounded, causing the 60hz ground loop hum.