Ground loop with an external USB card?? Help! (LONG)

**vettejock99** · 12-13-2005, 12:59 PM

Anyone want to take a crack at this perplexing problem? I have been running my carpc for a couple of months now and it works well except……I have this alternator whine that is driving me crazy! Anyway, I have been trying to troubleshoot this using some sort of logical approach, and as best I can tell, the problem lies with my USB sound card, which I bought because of the great recommendations it received from other carpc owners (and it does sound awesome when the whine isn’t there!).

So, I have a Shuttle-type AMD64 Sempron w/Nvidia 5200, Audigy 2 NX USB, SIR-ALP1 Sirius receiver, wireless card, USB Bluetooth dongle, and Xenarc touchscreen running off of a 400W Coleman inverter. It feeds into an Audiobahn 6601X 6-channel amp which is then wired back into my factory harness to output to the 6 factory speakers on my Chrsyler 300C.

Here is what I’ve tried and what I know, starting with the USB sound card connected, but the Sirius disconnected to minimize possible sources):

1) engine off, no whine, sounds AWESOME, even with the cheapo factory speakers
2) engine on, whine present, remove RCAs in to amp and no more whine (this means the amp and speakers have no loop, anyway)
3) plug in RCAs, whine present again. NOTE: changing cables (I have Monster cables 3.5mm to RCA) doesn’t help. When plugging in, if only 1 cable (pair of RCAs) feeding any two channels is present, I hear a LOUD hum in amp….sound drops to the standard high-pitched whine when 2nd RCA pair is plugged in. Is this evidence of the ground being worse until the 2nd pair permits additional flow THROUGH the amplifier? Dunno, I’m EE challenged…)
4) All RCA ends plugged in, I next remove the 3 3.5mm ends from the Audigy 2 – no whine. I plug them into 3 turned off mp3 players I have just for grins to see if it is some strange electrical ghost – STILL NO WHINE. Looks like it is the PC or USB adapter…. Plug it back in to USB adapter, whine returns….
5) Screw wire into outside of case of PC where it also screws into PSU and ground to car…..no improvement. Screw 2nd wire into chassis of PC and then to same ground as before – no improvement.
6) Disconnect Audigy 2 NX from PC and disconnect power from USB sound card as well. WHINE STILL PRESENT! As best as I can tell, this is a plastic case, and it is not making contact with anything metal that might be an alternative ground, so what the heck????

I don’t know what to do next, folks. I guess I could try ground loop isolators but I didn’t want to because a) I want to figure this out, b) I understand they can adversely affect sound quality, and c) I would have to buy THREE of them to cover the 3 RCAs used to drive my 6-channels.

Does anyone have any other ideas? FWIW, I have also previously plugged the 3.5mm jacks into the onboard sound of the PC motherboard (it supports 6-channel, just not powerful enough for good loud sound) and the whine was there, so it almost seems to me that it is something about the amp flowing current back through any device plugged into it with more than one cable…..I know, I don’t know jack about this, maybe it is just more likely that the PC has some ground issues too which I’ll have to address later, but I can’t see how. I have been testing with the PC sitting on cardboard as I’ve removed the mounts while I troubleshoot this grounding issue.

Okay, enough for now – any help would be HUGELY appreciated!

**vettejock99** · 12-13-2005, 02:47 PM

BTW, I have also pretty much ruled out the inverter as the cause, I think, because a) the whine is there even when the Audigy has no power plugged in and b) if I plug it all into an extension cord from the house instead of the surge protector plugged into the inverter, it is....still there.

**Will Albers** · 12-13-2005, 03:23 PM

Originally Posted by vettejock99

1) engine off, no whine, sounds AWESOME, even with the cheapo factory speakers.
2) engine on, whine present, remove RCAs in to amp and no more whine (this means the amp and speakers have no loop, anyway) -incorrect assumption. You need to use grounding plugs (RCAs where the inner and outer cables are shorted) plugged in to test if amplifier is causing noise
3) plug in RCAs, whine present again. NOTE: changing cables (I have Monster cables 3.5mm to RCA) doesn’t help. When plugging in, if only 1 cable (pair of RCAs) feeding any two channels is present, I hear a LOUD hum in amp….sound drops to the standard high-pitched whine when 2nd RCA pair is plugged in. Is this evidence of the ground being worse until the 2nd pair permits additional flow THROUGH the amplifier? Dunno, I’m EE challenged…) -unsure on the one vs two plugged in, my guess is it is cutting the differential by 2 when you plug in both lowering the given noise compaed to all on one. Not surprised by this though.
4) All RCA ends plugged in, I next remove the 3 3.5mm ends from the Audigy 2 – no whine. I plug them into 3 turned off mp3 players I have just for grins to see if it is some strange electrical ghost – STILL NO WHINE. Looks like it is the PC or USB adapter…. Plug it back in to USB adapter, whine returns….
5) Screw wire into outside of case of PC where it also screws into PSU and ground to car…..no improvement. Screw 2nd wire into chassis of PC and then to same ground as before – no improvement. -Hmm, this fixed mine
6) Disconnect Audigy 2 NX from PC and disconnect power from USB sound card as well. WHINE STILL PRESENT! As best as I can tell, this is a plastic case, and it is not making contact with anything metal that might be an alternative ground, so what the heck???? -my amplifeir does this as well when power is off on the PC. I get your whine... it goes away when the computer turns back on. Im sure it has to do with how the SB cards handle their output when there is no power. again, not surprised.

I don’t know what to do next, folks. I guess I could try ground loop isolators but I didn’t want to because a) I want to figure this out, b) I understand they can adversely affect sound quality, and c) I would have to buy THREE of them to cover the 3 RCAs used to drive my 6-channels.
-try them and asee if they adversely affect the sound. You may not notice

Try snipping the ground on the USB cable. You are experiencing a difference of resistance through your grounding. Sounds like the amps signal is grounding through the signal wires, through the audigy to the USB cable and into the PC. Make sure everything is grounded to the same point. I have read of people on this forum having luck with this.

My amplifiers have a switch for floating or common grounding. This is a great tool to have for situations like this. I'm guessing your amp does not. Do you have the amp physically mounted to metal? try unmounting it.

Tried a set of headphones?

**vettejock99** · 12-13-2005, 06:29 PM

Originally Posted by Will Albers

Try snipping the ground on the USB cable. You are experiencing a difference of resistance through your grounding. Sounds like the amps signal is grounding through the signal wires, through the audigy to the USB cable and into the PC. Make sure everything is grounded to the same point. I have read of people on this forum having luck with this.

My amplifiers have a switch for floating or common grounding. This is a great tool to have for situations like this. I'm guessing your amp does not. Do you have the amp physically mounted to metal? try unmounting it.

Tried a set of headphones?

Thanks for the input. My amp is mounted to the metal bottom of the trunk via screws through the carpet, and it is grounded there about 18-24" away with some 8 gauge cable (I think it is 8 gauge, maybe 10). I hadn't tried unmounting it yet because there was no whine with the inputs totally disconnected, but I can try it.

I haven't tried headphones from the USB instead of going into the amp, I can try that.

Regarding the ground wire on the usb, where is that? Do you mean the prong on the power adapter for the USB sound card? This card only has the 2 prong configuration - in fact I thought that too might be exacerbating this problem...

**3onDubs** · 12-13-2005, 07:58 PM

Originally Posted by vettejock99

Regarding the ground wire on the usb, where is that? Do you mean the prong on the power adapter for the USB sound card? This card only has the 2 prong configuration - in fact I thought that too might be exacerbating this problem...

The ground wire on the USB wire runs through the USB cable from end to end. You'll have to open up the cable and find which wire is the ground wire out of the bunch and snip it (i believe). I think there was a thread on how to do this, but I'm not sure.

**Will Albers** · 12-14-2005, 07:23 AM

unmount the amp. That may be your problem

**vettejock99** · 12-14-2005, 03:48 PM

Originally Posted by 3onDubs

The ground wire on the USB wire runs through the USB cable from end to end. You'll have to open up the cable and find which wire is the ground wire out of the bunch and snip it (i believe). I think there was a thread on how to do this, but I'm not sure.

FWIW, I did cut the negative wire on a USB cable and it didn't help. I then cut the positive wire and still no change. I cannot easily try the headphones due to the layout of the car, but I can try that later. It will also take a bit of work to dismount the amp, but I will have to try that next I suppose.

I think we're on the right track, though. What you've said at least seems to reflect what I suspect is happening, anyway. These suggestions are great - thanks! If I eliminate the whine I will post it here for the sake of those to come

**vettejock99** · 12-16-2005, 02:37 AM

As an update, I unmounted my amp - While is still there. So........I go and buy 3 ground loop isolators and......whine is still there.

Anyone know what I should try next?

**Will Albers** · 12-16-2005, 10:08 AM

We still need to determine if the sound is your amplifier or computer. Did you get a pair of headphones?

**Darmie** · 12-19-2005, 01:41 AM

Hi. Darmie here.

Not that I have a car computer in the miata, but ran into a problem with a new amp where I had the same noise that you are having. Did everything, I thought, then, I took some wire, wrapped it around one of the ground rca wires near the connector, and grounded it to the car. whine went away. Studying reviled that sometimes the alternator will present an RF signal that the cables can pick up and when you ground out the ground wire, it does not allow the cables to pick up the radio frequency of the alternator.