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

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

    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!

  • #2
    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.

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    • #3
      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?
      Take my advice: Do not try to build a system that includes EVERY feature. Start with the basics, build it to a bug free state, and THEN add on.

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      • #4
        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...

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        • #5
          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.
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          • #6
            unmount the amp. That may be your problem
            Take my advice: Do not try to build a system that includes EVERY feature. Start with the basics, build it to a bug free state, and THEN add on.

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            • #7
              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

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              • #8
                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?

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                • #9
                  We still need to determine if the sound is your amplifier or computer. Did you get a pair of headphones?
                  Take my advice: Do not try to build a system that includes EVERY feature. Start with the basics, build it to a bug free state, and THEN add on.

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                  • #10
                    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.
                    My first computer install 2001 SS camaro
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                    My latest project. Much better. 2003 Mazda Miata
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                    • #11
                      There is a problem we come across every once in a while. Blown ground or grounds on the head units. What leads me to believe you may have this problem is that you get a loud hum when both your RCA plugs are not connected.

                      Blown grounds on source units are caused when the power grounding on the amplifier is poor or gets interupted for some reason. At this point the amp gets it's power ground through the RCA sheilds and the source unit. Now since the current draw from the amp can be hundreds of amps the foil on the printed circuit boards in the source unit can not take that kind of load and what happens is that the copper foil on the pc board of the source unit burns and creates a open circuit. If the RCA outs on the source unit have seperate paths to ground on the Printed circuit board then lift one or the other and you get a loud hum. If both are blown you get low output or very loud hum or whine, all depending on what ground paths are left available.

                      You can tes this by using a multimeter and checking for continuity first between the grounds on the RCA jacks on the source unit. You should get a short circuit indication. Next check the continuity of each RCA jack ground to a known good chasis ground. Even if the RCA ground on the source unit is isolated from chasis ground most amplifier audio grounds are not. Again you should have a near short circuit indication between RCA and chasis ground. If you do not have this indication in any of these tests it means that the grounds on the source unit have opened up and that needs to be corrected.

                      Another way to test this is to use a different source unit, such as a walk man or such. If the wnine goes away then the problem is in the sound card.

                      If you find that the grounds are blown then before replacing or repairing the unit, you need to thoroughly check the ground path from the amp to the battery and make sure that it is and remains a solid connection.

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                      • #12
                        on my system for what ever reason, when i went from 8 AWG to 2 AWG for the main power to the trunk, i got rid of my alt wine,
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                        • #13
                          Originally posted by accentsound
                          There is a problem we come across every once in a while. Blown ground or grounds on the head units. What leads me to believe you may have this problem is that you get a loud hum when both your RCA plugs are not connected.

                          Blown grounds on source units are caused when the power grounding on the amplifier is poor or gets interupted for some reason. At this point the amp gets it's power ground through the RCA sheilds and the source unit. Now since the current draw from the amp can be hundreds of amps the foil on the printed circuit boards in the source unit can not take that kind of load and what happens is that the copper foil on the pc board of the source unit burns and creates a open circuit. If the RCA outs on the source unit have seperate paths to ground on the Printed circuit board then lift one or the other and you get a loud hum. If both are blown you get low output or very loud hum or whine, all depending on what ground paths are left available.

                          If you find that the grounds are blown then before replacing or repairing the unit, you need to thoroughly check the ground path from the amp to the battery and make sure that it is and remains a solid connection.
                          I think you may be on to something here. Today I finally got a chance to do more testing. I had unscrewed the amp from the carpeted trunk floor, and I took the PC off as well to try to eliminate the mounts as the ground problem. Noise still there. I reassembled, using rubber washers whenever I could - noise still there. So, I did the headphone test and - I cannot hear the whine. It is tough with the headphones because at any given time I can only get center/sub, front l/r, or rear l/r, so it is not as "loud", but still, I think it was gone.

                          Then I plugged the MP3 walkman in again. Again - it was gone....but wait, maybe not! Seems like I can faintly hear the noise in this scenario....again, it is harder to tell because of the whole 2/channel limitation, but it does seem like it is there.

                          If so, does that mean that basically a) the amp ground is bad or b) it has the short condition you mentioned? It seems to work "fine", but the very first time I turned it on the amp shop which had installed it hadn't connected the ground (they didn't tell me, they were waiting for me to decide where exactly I was going to screw the amp down). Not good, but I powered off and got it connected securely to an unpainted portion of the chassis.

                          Would most custom/high-end sound shops have the piece of equipment you mentioned? I know most of the Circuit City-type shops say their multimeters can't help them with this. I am ready to pay a shop to tell me exactly how to fix this.......everything else works beautifully but this high-pitched whine is killing my hearing.

                          Thanks for this very valuable info!

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                          • #14
                            I used to work for a high-end audio shop, and therefore have seen my fair share of customers coming in with the dreaded "alternator whine". From a very basic standpoint, first ensure that the power and ground cables to the amplifier are of adequate capacity. With an amp if this size, you should be using *at least* an 8 AWG conductor on *both* power and ground. They should both have good connections at each endpoint, and the power wire should not be run near any vehicle wiring, if at all possible. If I remember correctly, your 300 has the battery in the trunk, no? This would obviously work to your advantage here. Also, try to avoid running the signal cables (RCA's, RCA-to-1/8" adaptor) near any vehicle wiring. Your 2-channel tests make all the sense in the world - it's hard to determine how much whine you've got when you have only 33% of the system running. Although I've never worked with the Audiobahn equipment, I don't know that it's known for sound quality - it may not have sufficient noise-cancelling and grounding as the higher-end amps do.

                            FWIW, I have *never* had to use ground-loop isolators, noise-filters, etc. to rectify a problem - IMHO, they're merely band-aids for the underlying problem. Start with the basics - maybe plug the Audigy into a laptop running on battery. If that's not an option, maybe run it off a PC that's not in any way attached to the car. Maybe pick up a couple 1/8" stereo Y-adaptors so that you can get all six channels plugged in to one device.

                            In short, if it were mine to do, I think I'd try swapping out components and substituting things one at a time until the problem goes away (after ensuring the power/RCA requirements first). You seem intelligent enough to tackle this - don't let it get the best of you.

                            Alternator whine is a pain in the *** to find in the first place, and the complexity added with a PC just exacerbates the whole scenario.
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                            • #15
                              Originally posted by Daley
                              I used to work for a high-end audio shop, and therefore have seen my fair share of customers coming in with the dreaded "alternator whine". From a very basic standpoint, first ensure that the power and ground cables to the amplifier are of adequate capacity. With an amp if this size, you should be using *at least* an 8 AWG conductor on *both* power and ground. They should both have good connections at each endpoint, and the power wire should not be run near any vehicle wiring, if at all possible. If I remember correctly, your 300 has the battery in the trunk, no? This would obviously work to your advantage here. Also, try to avoid running the signal cables (RCA's, RCA-to-1/8" adaptor) near any vehicle wiring. Your 2-channel tests make all the sense in the world - it's hard to determine how much whine you've got when you have only 33% of the system running. Although I've never worked with the Audiobahn equipment, I don't know that it's known for sound quality - it may not have sufficient noise-cancelling and grounding as the higher-end amps do.

                              FWIW, I have *never* had to use ground-loop isolators, noise-filters, etc. to rectify a problem - IMHO, they're merely band-aids for the underlying problem. Start with the basics - maybe plug the Audigy into a laptop running on battery. If that's not an option, maybe run it off a PC that's not in any way attached to the car. Maybe pick up a couple 1/8" stereo Y-adaptors so that you can get all six channels plugged in to one device.

                              In short, if it were mine to do, I think I'd try swapping out components and substituting things one at a time until the problem goes away (after ensuring the power/RCA requirements first). You seem intelligent enough to tackle this - don't let it get the best of you.

                              Alternator whine is a pain in the *** to find in the first place, and the complexity added with a PC just exacerbates the whole scenario.
                              Sorry I haven't updated this thread in a while. The advice has been helpful, and I'll be buying a multimeter today. I actually took the car back to the Circuit City that did the amp install (they have been very, very cool, but although they get a few car-Xbox installs, a carpc is definitely a step for difficult for them). The guy spent several hours tracking every wire and seperating the signal wires from the power to run tests, and the whine is still there. The gauge is fine, the grounds seem good, but it's still there. I think it must be the amp, so I am going to buy a new one, I guess. If it isn't that, I don't know what to do...

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