grounding problems; static sounds in my monitors

[jkvd]

Hi there,

I'm having some problems with unwanted signals in my monitor speakers.
This is my setup as it is now:

- ungrounded pc
- firewire interface powered by pc
- unbalanced audio connection (no balanced options) to powered monitors (grounded

I know this doesn't look like a great solution, but grounding both the monitors and the pc gave much more and a different noise. The cpu fan speed affected the sound of the intereference. Just grounding the pc gave the same effect.

Changing the volume on the softmixer of the interface didn't affect the volume, so I guess there's just some static energy in the interface's case that travels on the ground of the unbalanced audiocable to the monitors.
You'd say that the interface is grounded through the computer that has grounded power connection, but that gives the worst signal.

Anybody any clues to the problem and the solution?

Jaap

 

[dgatwood]

Hi there,

I'm having some problems with unwanted signals in my monitor speakers.
This is my setup as it is now:

- ungrounded pc
- firewire interface powered by pc
- unbalanced audio connection (no balanced options) to powered monitors (grounded

Disconnecting the power line ground on a computer is never acceptable. They were not designed to operate in an ungrounded environment and do not comply with FCC interference regulations when you use them that way. No matter what, that is not the correct way to solve the problem.

When you use them in this fashion, 100% of all the noise the computer generates is being dumped through the shields of your audio connection and transmitted to the device at the other end. If the case of the next device isn't grounded solidly, it then turns into a giant antenna. Oh, and most devices' case grounds suck, so this pretty much happens every time you hook an ungrounded computer up to any audio device at all whatsoever.

I know this doesn't look like a great solution, but grounding both the monitors and the pc gave much more and a different noise. The cpu fan speed affected the sound of the intereference. Just grounding the pc gave the same effect.

Are you grounding both the computer and the speakers from the same power outlet? You need to make sure that the ground really is common between them, which means putting them on the same circuit (at least).

Changing the volume on the softmixer of the interface didn't affect the volume, so I guess there's just some static energy in the interface's case that travels on the ground of the unbalanced audiocable to the monitors.
You'd say that the interface is grounded through the computer that has grounded power connection, but that gives the worst signal.

Two things: make sure your outlet's ground is solidly grounded. Assuming you check the grounding at the breaker box and at the grounding rod outside and it looks sane, there's probably something else wrong, like a lousy computer power supply that isn't grounded properly.

Fortunately, this is usually relatively easy to fix with ground bussing. Take an unused audio jack on each device (or a metal case screw or...) and fasten a wire to the ground of a plug/spade as needed to hook up to it. Be sure to use a heavy gauge wire---say 10 AWG. Connect all of these together. Then take a power plug and fasten a wire of a similar gauge to the ground pin on that plug. Attach this wire to the bundle of grounds.

NOTE: not all screws are viable for grounding purposes. Painted screws are bad, as are screws that don't go into the frame of the device. A painted screw might be okay if it screws into bare case metal, though.

A good place to ground a computer is the metal plate on the back of a PCI card (NOT the screw at the top of an empty slot). In particular, I get a good ground by slipping a spade under one of the screws on a VGA connector (between the screw and the little extender nut that's built into the card).