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HELP: Ground Loop Culprit

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  • HELP: Ground Loop Culprit

    Excuse my noobiness about car audio but I've done the searches and read the FAQs but I can't find a solution to the problem I'm having. I can't find where the ground loop is coming from. When I turned on the ignition, there is a small delay before my PC is turned on. During the delay or when I manually turn off the PC, the whining noise is most apparent. It's definitely alternator whine since it increases when I accelerate. The whining noise is greatly reduced when the PC is turned on.

    So I'm thinking the amp is creating the noise when it's not receiving any audio signal. My amp and PC are grounded at different spots, since my PC is in the front and amp is in the trunk of the car. Ground cables are relatively short. I've tried a ground loop isolator but it's no help. All connections are good.

    Does anyone have any idea on where the source may be and how I can fix this? It's driving me mad.
    02 Accord Coupe EX V6

  • #2
    short grounds really won't make too much of a difference, i would recomend trying to ground the setup in the same place, or run a ground wire back to the battery.

    i am having a very similar issue, i have a post that is probably on the same page as this thread, so look there for some other trouble shooting that you can try (i am planning on rewiring my setup in the very near future, so i have been dealing with it for now)
    My OLD 2001 Mitsubishi Eclipse GT:
    "The Project That Never Ended, until it did"


    next project? subaru brz
    carpc undecided

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    • #3
      From what I understand from your other thread, I think we're actually having the opposite problem. The noise is only present when your PC is on while mine is most apparent when mine is off. I do hear a little hum when mine's on but when it's off, it can get pretty annoying. I was hoping I'm missing something minor so I wouldn't have to do all the rewiring.
      02 Accord Coupe EX V6

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      • #4
        have you tried grounding the shield of your rcas? this will sometimes work to get rid of noise, but in my problem, made it worse.

        my problem is that it will whine only when the factory circuits are energized- carputer on or off-- as long as i leave the key in acc(only the carputer, stereo system on) there is no whine(my main power run is on top of the factory wire loom going to the back of the car, so this could be part of the issue).
        My OLD 2001 Mitsubishi Eclipse GT:
        "The Project That Never Ended, until it did"


        next project? subaru brz
        carpc undecided

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        • #5
          Can you elaborate on what you mean by grounding the shield of the RCA's?

          I believe reason why you're not getting any whine when you are in ACC only is because your alternator is not actually running. Mine is the same way -- if I don't turn my engine on (ACC only) there is no whine. But when my engine is running and my PC is off, the whine is very apparent. And then when the PC is actually on after the SDC delay, the whine is decreased dramatically.
          02 Accord Coupe EX V6

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          • #6
            mine will whine only when the key is to the 'run' position(when the engine computers are getting power), it makes no difference if the engine is on or off, but if it is running, it will also get alternator whine.

            for grounding the shield of the rcas, take a small peice of wire and attach it to the outside metal part(shield) of the rca, and then attach it to the closest ground.

            i ususally do it right on the amps-- with everything running, you should be able to notice a immedeate difference, wether it works or not.
            My OLD 2001 Mitsubishi Eclipse GT:
            "The Project That Never Ended, until it did"


            next project? subaru brz
            carpc undecided

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            • #7
              I will give that a try. Thanks, soundman.
              02 Accord Coupe EX V6

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              • #8
                I am having the same issue with my alternator whine. I have rewired and regrounded every component 3 times and its still there. Having done so many cars I am getting very frustrated that I cant fix my own. I never had an issue with my previous system that had a headunit so I know the computer is the problem I just cant get it to stop. It is especially bad when I tether my phone to go online. I can hear the data stream from the computer in my subs.
                Going to try another ground tomorrow but that will be number 4 and doubt it will fix it. Im figuring its an isolation issue in my pc that is allowing induced noise into the audio out of the computer.
                Google my name if you need to know who I am.

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                • #9
                  how do you deliver power to the PC ?
                  inverter ? PSU ?
                  ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
                  2007 Toyota Tundra Double Cab SR5
                  >"Say what you mean and mean what you say"<

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                  • #10
                    M2-ATX power supply
                    Google my name if you need to know who I am.

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                    • #11
                      I was hoping I didn't have to rewire my whole car since I moved out to an apartment now and I don't have the garage anymore. If you are rewiring your car anyway, do you want to give these possible solutions a try? Or if you already have tried any of it, please let us know which one didn't work. I tried a couple but it didn't work out for me.

                      -Ground PC and AMP to the same point
                      -Mute MIC or Line-In
                      -Make sure you separate power cables from audio cables
                      -Ground touchscreen?
                      -Ground PC chassis?
                      -If you have a metal PC case, make sure it doesn't touch any metal in the car
                      -Keep ground cable short

                      Let us know if any of these work or don't work. BTW, I'm using the OPUS 150 PSU.
                      02 Accord Coupe EX V6

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                      • #12
                        done all of that except the mic mute.
                        Google my name if you need to know who I am.

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                        • #13
                          the m-2 is notorious for noise issues, esp. when it is mounted in close proximity to the rest of the computer components, but should not be be the cause of the data stream interferance. if possible, you could try to shield or movethe m2 a little farther away from the other components.

                          it goes against every audio installers recomendations, but i am starting to plan for rewiring my system, for both power and ground going straight to/from the battery(thats right, i will not be using the chassis for ground) and running all of my stereo, and computer stuff off of this. so far, it is one of the best ways i can come up with to completly isolate the entertainment electronics from any car ecu issues.
                          My OLD 2001 Mitsubishi Eclipse GT:
                          "The Project That Never Ended, until it did"


                          next project? subaru brz
                          carpc undecided

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                          • #14
                            If your going to do that there is a wrong and right way to do it. The wrong way is both lines being the same guage. The right way is if your using 4 guage power use 2 guage ground. Always step the ground wire up one size bigger than your power. The reasoning for this is the resistance you are going to create on that ground wire being so long can cause a fire or heat up your components to the point of destruction. I always explain it to people like this. The power is a thick milkshake and your wire is the straw. If you have a bigger straw the easier it is suck up the milkshake, too small of a straw and your face turns red and head wants to explode. Your head is the equipment struggling to get the current it needs. The ground is the same way only the straw is full of milkshake and your blowing it back in the cup. Bigger the straw easier to blow the milkshake out, too small and same result as before.
                            Google my name if you need to know who I am.

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                            • #15
                              thanks for the reminder! i almost completely forgot about it- i knew that is how it had to be, and i remember thinking that i had to do it that way, but it just completly slipped my mind as i started looking at wire (trying to keep the overall cost down)...
                              My OLD 2001 Mitsubishi Eclipse GT:
                              "The Project That Never Ended, until it did"


                              next project? subaru brz
                              carpc undecided

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