I'm getting terrible alternator whine on my USB soundcard if I run it from the main 12v car supply, but it's OK if I run it from the PC 12v power supply.

I take this to indicate that the noise comes from within the main power lines, and the Opus cleans it up before distributing it.

However I would like to run the s/c directly from the car so I can have it turned on without the PC (so line-in from the radio will play, even if the PC is off).

To this end, I've just bought a noise suppressor:





Unfortunately it didn't come with any instructions, so I'm after a bit of help.

My assumption is that the red wire goes to the battery, the black wire is connected to ground and the yellow is the "clean" power supply for the sound card. Am I correct?

Also, should it go close to the battery, or close to the PC, or does it not matter?

I'm getting quite a lot of FM interference in the car since installing the CarPC - the main power supply cable runs the length of the car - if this contains a noisy power supply, can it radiate EMI throughout the car?

Thanks

Ian