Gnd loop..a potential solution

**Matthew230** · 10-29-2004, 05:33 PM

Good evening,

I have built and installed everything to perfection, except for my noise issue, (high pitched tone, alternator whine, mouse and HD activity noise)

I have taken it apart and tried to identify the source of the noise with a plethora of different tests. It comes down to the noise being present when the PC is switched on and the audio lead is plugged in, even with everything else disconnected.

I have it running through the audio feed from the CD changer, though have tried it with other sources such as portable CD player and it runs fine.

I tried a ground loop isolator, but I couldn't hear the music, just made things worse.

I obviously lack the technical expertise to solve this issue, as I have spent many hours trying.

So my new solution - Add a digital output to my sound card, hopefully this will send out a clean sound then further down the line a digital - Analouge converter.

Will this work? Or is there any other solutions to my noise that I haven't thought of ????

Many thanks for everyone's time and help.

Matthew

**Grayscale** · 10-29-2004, 05:36 PM

i had to unground my motherboard from the case, sounds silly i know but yeah. optical isolation would definately work though.

**Matthew230** · 10-29-2004, 05:37 PM

Originally Posted by Grayscale

i had to unground my motherboard from the case, sounds silly i know but yeah. .

How did you do that ??

**zPilott** · 10-29-2004, 06:51 PM

I thought about that too, but the D/A converter is the hard part

**Grayscale** · 11-02-2004, 07:00 PM

Originally Posted by Matthew230

How did you do that ??

It's a custom case I made, so didn't have to worry about metal touching it or anything. I just put slices of balsa wood between the case and the standoffs and the panel that touches the ports i used a simlar technique to keep it from grounding.

**sq_geek** · 11-20-2004, 01:13 PM

Grayscale, did the isolation of the motherboard from PC case make your noise go away 100% or just only help reduce the noise?

What I don't get is how is the motherboard or PSU grounded to the PC case? I don't see any wires connecting into the metal case, but my voltmeter clearly shows my case is indeed grounded.. Any idea how?

I'm thinking it would be easier to block the case from being grounded rather than building a noise-resistant case...

**netboy** · 11-20-2004, 02:02 PM

First of all isolate where the alternator whine is coming from, amp, rcas or computer. Unplug the rcas from the computer, if the whine goes away then the noise is coming from your computer, if you still got whine then unplug the rcas from the amp. if your whine goes away then it is coming from your amp, if it is still there then it is coming from your amp. Do this then let us know so we can further help you.

**Matthew230** · 11-20-2004, 02:16 PM

Originally Posted by sq_geek

Grayscale, did the isolation of the motherboard from PC case make your noise go away 100% or just only help reduce the noise?

What I don't get is how is the motherboard or PSU grounded to the PC case? I don't see any wires connecting into the metal case, but my voltmeter clearly shows my case is indeed grounded.. Any idea how?

I'm thinking it would be easier to block the case from being grounded rather than building a noise-resistant case...

If your case is metal and your PSU is screwed into it with metal screws, then there's your ground. The motherboard is also grounded via the ATX wire.

**Cat Monkey** · 11-20-2004, 02:18 PM

Originally Posted by sq_geek

Grayscale, did the isolation of the motherboard from PC case make your noise go away 100% or just only help reduce the noise?

What I don't get is how is the motherboard or PSU grounded to the PC case? I don't see any wires connecting into the metal case, but my voltmeter clearly shows my case is indeed grounded.. Any idea how?

I'm thinking it would be easier to block the case from being grounded rather than building a noise-resistant case...

tis grounded via the spacers

**sq_geek** · 11-21-2004, 02:06 AM

Originally Posted by Matthew230

The motherboard is also grounded via the ATX wire.

What ATX wire? I pulled my PSU (DC-DC) out entirely and left the wires hooked up -- it made no difference...

Originally Posted by Cat Monkey

tis grounded via the spacers

I thought it might be. Is that both on top and bottom? (Would adding a red felt washer which came with the case help or would I need one on each side of the motherboard mounting hole?)