[alesak]

Hi guys,

I was having this wierd problem: when moving the mouse in windows, scrolling, reading from HDD, rendering anything with GPU etc... variable high-frequency noise came from my speakers. Not headphones, only speakers. I thought my onboard sound card was dying, so I got new USB sound card, which did not help one iota.

I ruled out problems with drivers: this issue happened even in BIOS. When I was holding any key, it made a noise. Disabling onboard sound or some fancy Gigabyte motherboard features(C1 nad EIST) did not help.

After a lot of painful googling, I tried using cheater cables. After some messing around, I found that disconnecting only my PC from ground solves the problem. Also, connecting PC to power socket with different ground solves the problem.

How is that possible? Common wisdom is that everything should be on the common ground, i.e. common power socket, so that ground loop hum doesn´t happen. What could be wrong here? I´ve got metal case, my PSU is pretty good and connected to MOBO(GA-EP35-DS3) in usual way and mounted on the case with screws that came with case.

[Bobnova]

Makes me wonder how groundy that ground really is.

[alesak]

How exactly do I measure that groundilessness of my ground?

[Diggrr]

There are AC/ground plugs that can check a live plug by simply plugging them in. The three neon lights in them will show you if you have a faulty ground.
Backup method: Turn off the breaker to that circuit. Double check that it's turned off. Use a multi-meter set to read Ohms and check between the ground pin hole and the two power holes one at a time, between the neutral (white wire/longer of the two slots) and ground should be very low resistance (if any) because they usually are connected at the breaker panel.

You should also do a visual inspection of the ground cable. Follow it from the breaker panel all the way outside. It's a large uninsulated twisted copper cable. It should go outside to a ground steak, or on the inside to a metal water pipe coming into the house from the city water (NOT gas!! seen that once). Check to make sure connection points are solid and not corroded or green.

My Belkin surge protector/power strip has an indicator light that glows red with a faulty ground. That's a good option as well.

[Diggrr]

BTW, if any of these things result in finding a problem, get a licensed electrician to handle them. You could move your computer to another power plug, but the problem will still remain.
Waking up dead will suck.

[alesak]

Thanks a ton!

Originally Posted by Diggrr

Waking up dead will suck.

Especialy if there will be zombie-hunters around.

[bmwbaxter]

If switching to a different plug helped, then no need to check your main ground. Sounds like you have an open ground somewhere. So shut off the power and check all the outlets on that circuit to ensure they are all wired up correctly. If you don't feel comfortable doing it yourself don't! No point putting yourself in any risk you don't want.

[alesak]

I guess I will try plugging my junk into different outlets using different power strips, to see where the mistake is.

Also, if the ground is open, doesn´t it mean that cheater cable should have had no effect? Since open ground means no ground(AFAIK).

[johan851]

Also, if the ground is open, doesn´t it mean that cheater cable should have had no effect? Since open ground means no ground(AFAIK).

Maybe. There could be a long run of wire that's picking up some noise, though. Or it could be physically connected to some other appliances that are also dumping noise to ground, like a refrigerator. It may connect to who-knows-what, but never connect to ground.

[larrymoencurly]

Ground loop problem? Ground Loop FAQ

If it's not a ground loop, I'd try an AC line filter that consists of both capacitors and chokes. It's possible the amplifier for the speakers doesn't have one, but if your computer power supply is super cheap, it may not have one, either. To find out, get a portable AM radio operating off batteries, tune it to a weak station, and and hold it near the computer while only the computer is turned on (turn off amplifier, printer, even monitor). I had a cheap PSU that would drown out stations even when it was 20 feet from the radio, but a good PSU caused no audible interference even when the radio was only 3 feet from it. Some surge protectors and I believe all APC backup power supplies contain decent line filters. Unfortunately most of them have the filter between the whole unit and their power cord, not between each outlet on the unit, so they won't block inteference when everything is plugged into them.

[johan851]

The Tripp-Lite ISOBAR power strips have good filters between pairs of outlets and they're nice units for the price. I'd recommend those highly.