BUZZ when connecting turntable to PC

[raveon]

Hello out there.

I have a problem with noise when I connect my phono preamplifier to the soundcard in my pc.

Let's start with the signal chain:

Turntable>phonopreamp (NAD PP2)>Behringer UB802 mixer>soundcard (M-Audio 2496)

The problem is, that I get a buzz-noise, when I record to the HD.
According to Adobe Audition 1.5 (AA) this buzz is about -54dB. I can reduce the buzz to -84dB with noise reduction in AA, but I would much rather prefer not to. The less manipulation with the original signal the better.

When I pull out the cables from the turntable to the phonopreamp the buzz disappears (yes I do have a connection frem the turntable chassis to the the ground plug on the preamp).

The buzz also is absent, when I feed the mixer into my stereo setup. Even with the volume turned all the way up - with my ears close to the speaker - there is no buzz, just some hiss.

Connecting the mixeroutput to the soundcard on my laptop generates no buzz either, so I guess it is all a matter of grounding or groundloops.
The pc is not grounded - just live & neutral - but as far as I know: in the PSU there are to smallvalued capacitors, one from live and one from neutral connecting to the pc chassis, which is the signal ground too. That could be the problem? Or am I wrong?

Any suggestions to solving this irritating problem will be very appreciated.

Regards

raveon

"keep on rockin' in the free world"

[Geek]

Two things come to mind:

- AC pickup from your house wiring. In the colder months, more current is drawn because of heaters and festive lighting. This causes a greater AC magnetic field everywhere. Try re-orienting your turntable (rotate it, or move it about the room with the volume up and no record playing and look for a position of minimum hum). Try re-orienting the lay of your cables too.

- Ground loop. Do you have a way of lifting the ground to your soundcard from your phono pre without breaking the signal?