Will an optical link fix my ground loop?

vettejock99 · 02-11-2006, 09:01 PM

All -

I am going to try to approach this alternator whine problem I have in a new way. As many of you know, I've determned at least that it is not my amplifier. However, no amount of grounding, rewiring, or other troubleshooting has fixed my issue which appears to be as simple as an electrical differential existing which is causing electricity to flow from my PC to my amp via the RCAs, causing an obnoxious alternator whine. So, my USB sound card has a TOSLINK optical digital output. If I buy another USB sound card (eg. Audigy NX) which has an optical in (or some sort of other external digital sound processor/DAC) then that should eliminate the ground loop, because it won't traverse the optical link, right?

I know this may seem like a sledgehamer approach but I assure you, I have spent far, far too long trying to isolate this noise from entering my amp, so whatever works now.

Mark

numbers · 02-12-2006, 12:33 AM

An optic cable is indeed the perfect solution for a ground loop, but I don't quite understand your proposed configuration. You need a converter at the amp to feed the optical signal into the analog input of the amp.

nkotch · 02-12-2006, 12:47 AM

You need to elaborate a little more on how you are planning on doing this.

What is your current setup? (carputer, amps, HU, etc....) I know how annoying tracking down a whine can be but there may just be something that you haven't tried yet or a trick or work around that someone may come up with.

vettejock99 · 02-12-2006, 01:09 AM

I would use the optical SPDIF out on my PC soundcard to the SPDIF IN on the Audigy 2 NX external soundcard. The amp would still be connected to the Audigy 2 NX via 3 Monster 3.5mm stereo to RCA cables.

Anyone giving me odds on this working or not?

numbers · 02-12-2006, 02:42 AM

Yup. 0% chance of it working. You still have the same loop through the amp and sound card. The only way it will work is if you run optical out to a digital - analog converter, then rca as short as possible from the converter to the amp.

DarquePervert · 02-12-2006, 06:05 AM

You want to run optical from one sound card to another?
What is that going to accomplish, really?
You still have the analog output to your car audio system, so you've resolved nothing at all.

Now, if you were to get a DSP that will accept the optical link from the soundcard, that would resolve your issue. But that hardware ain't cheap.

vettejock99 · 02-12-2006, 11:14 AM

I don't entirely understand these last two comments, though they are along the lines of things I thought I might hear. I've determined previously that it is not USB sound card, it is somewhere at the actual computer or upstream. How would the loop cross the optical link? The only way I anticipated a loop still exisiting is possibly via the power supply to the external USB sound card or via its USB connector, but I was planing on snipping the power wires within the USB cable if that was a problem or not connecting it at all. Here is a simple diagram, with dashed lines - optical link:

PC (SPDIF out)-----------(SPDIF IN)AUDIGY NX-+RCA-+Amp
Pwr Pwr Pwr
I__________________________I_______Gnd__________I

I would think the optical link would break the loop, as it has no capability to carry the electromagnetical signal. ANyway, sorry it is a crap drawing, and I am probably wrong, I just didn't see the difference between using a second soundcard "backwards" and a DSP.

If the DSP is the route I have to go, can you recommend a model? I know some have popped up on this board, but it seems results are mixed. Thanks for the help guys, at least I am close - one way or the other. I can't take the frustration anymore.

numbers · 02-12-2006, 03:03 PM

You're giving mixed information. If the problem is at the computer or upstream, then it isn't a ground loop. If it's a ground loop, then it is almost certainly the analog cable between the sound card and amp. Either way, your proposed solution won't do any good.

vettejock99 · 02-12-2006, 04:25 PM

Quote: Originally Posted by numbers

You're giving mixed information. If the problem is at the computer or upstream, then it isn't a ground loop. If it's a ground loop, then it is almost certainly the analog cable between the sound card and amp. Either way, your proposed solution won't do any good.

If I plug a MP3 player into the sound card I do not get the whine. That seems to me to rule out the analog cable or the soundcard as the loop. Thus I am trying to sever it at the next point, the computer to the card. I haven't read anything that enlightens me as to why a DSP will work and my solution won't. That said, again, anyone recommend a DSP?

DigitizedLife · 02-13-2006, 09:29 AM

I am using the Radio Shack Catalog # 270-054 Noise Filter and it works well. If you have ground loop or alternator noise this filter removes all of it without harming the sound in any way!

vettejock99 · 02-13-2006, 09:44 AM

Thanks, DL, but I tried them nd they didn't help on my rig....

pip · 02-13-2006, 10:09 AM

Swap your amp for one with an optical in?

nkotch · 02-13-2006, 11:28 AM

Did you have your mp3 player plugged into the car's power when you used it? If not then it's not going to give you any problems because it's not using a separate ground like your computer is.

The problem with running an optical cable to an external sound card is that that external sound card will still be plugged into your computer and will still give you noise....both those sounds cards will share a ground with your computer, so you're not really bypassing the computer. The only possible way it might work is if that external sound card just happens to deal with ground noise better than the one you have in your computer now.

I think the only other choice is what Darque mentioned: some external DSP that could convert an optical signal to analog for your amp. But if you've already tried an audio isolator unit on the rca audio feed then I kinda doubt a different sound card or dsp unit would help.

You might have already seen it but saw this link in another thread:
http://www.epanorama.net/documents/g...oop/index.html

vettejock99 · 02-14-2006, 12:17 AM

I know, that's how I know it is the PC and not the sound card. I also snipped the power wires within the USB cable, but there is still the possibility of a loop.

Anway, that said, I am now looking for a DSP....

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