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  • Grounding question

    Searched around for this but didn't find the specific answer I was looking for. I'm pretty new to this, but I have installed a computer in my car. Everything is working fine but I get a background noise through the speakers when using the computer. Now, from what I've read in other threads this must be a grounding issue. My inverter is grounded to the battery and then an extension cord runs from the inverter to the computer in the trunk. Do I need to ground the computer seperately? Or is it grounded already since it gets power from the inverter?

    If I need to ground ym computer seperately, how would I go about doing that?

    Any help would be well appreciated. Thanks.

  • #2
    Lots of info on here having done a In fact maybe too much information?

    I think that if you can the PC case should be grounded by running a wire to a ground point in your car. Where one is depends on what make/model your car is. This run should be as short as possible so find a close one.

    What does the sound sound like? If it is mechanical mouse/disk noises then you may be getting internal interference on your onboard audio. Much less likely with a PCI card though. Many use an external USB sound card to avoid interference from the PC.
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    • #3
      Yeah, i searched for grounding and some other terms and it came up with over 14 pages of threads, most of them don't deal with what I'm asking specifically here.

      Anyway, the sound is like a buzzing sound, but it varies sometimes in pitch. I know it's not audio intereference because I can hook up my portable CD player to it and everything works fine. This leads me to believe that it is a grounding issue.

      Why do I need to ground the case? There is no electrical connection being made to the acutal PC case, so there should be no reason to ground it, right? You obviously don't need to ground it in a building.

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      • #4
        In a building it's grounded by the third prong on your ATX PSU. But a ground on your pc would help to get rid of any lingering charge, which could cause your hum. I switched RCA cables and haven't had a ground problem. I just used a common ground between my amp and ITPS.
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        • #5
          extension cord to back is gonna cause some interference. Your running AC power all along your car, i just hope your auidio cables are at least on the other side.
          Id say run the power cables from the battery to the back and make the AC power cord as short as possible. Keep distance between intvertor, PSU and mobo as short as possible.

          A changing pitch wine is usually caused by alternator wine. You should buy some better shielded audio cable or buy an external usb sound card and run USB wires to the front and as short analogue audio wire as possible, thats the best solution.

          Good chunky wires as short as possibly along with grounding invertor, PSU, mobo and case to the same point will help.
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          • #6
            This old chestnut...

            I've had noise with every install i have done, its a pain...

            Most noise i have got rid of quite easily, but this one was a bugger to solve..

            The time i had noise the same as your getting i ended up having to move the inverter to the rear of my car (where my carputer was located), no matter what i tried with this one i could not get rid of it any other way...

            Not sure why this was, i just think inverters must create a lot of noise, which when added to the power cable running the length of the car got picked up by the RCA's...

            I tried much better shielded twisted-pair RCA cables, this did next to nothing, i earthed everything in sight, used noise suppressers...and still made no difference.

            Moving the inverter to the boot cleared up all the interference when the PC was running, but i still had some noise for the first 12-15 seconds until my PC booted up, i tried everything to clear this, but had no luck...(It wasnt a major problem, i got around this by putting a timed relay on my amp, which only turned on my amp after 20 secs).

            Just make sure you earth everything with the earth cable being as short as possible...

            On another install i had some constant noise, which was simply fixed by adding a little earth strap from the mobo to the case chassis...

            Hope this helps, if not good luck...

            Daz

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            • #7
              Inverters create a huge amount of noise because of two factors, one, its more of a squarewave and squarewaves produce a large amount of harmonics, and two, the DC chopper a inverter uses to produce AC is like a RF generator that gets transmitted thoughout the car.

              I started off with an inverter in my car but switched to a DC-DC because of the noise.

              You might want to build a metal box around the inverter and ground the box, that will block alot of the RF noise, but not much can be done about the output squarewave, unless you place large caps on the output, hoping to turn the stepped signwave into a pure signwave.
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              • #8
                Ok, I attached a wire to my case via one of the screws that holds the PSU in the case and ran the wire up to where the inverter is grounded. Almost all of the noise was eliminated. Now background noise can only be heard if I turn the volume up really loud (so loud that I probably would never turn it up this loud due to fear of blowing my speakers out). I may go out this weekend and buy a noise filter thing from radioshack or somewhere to get rid of the rest of the noise.

                I want to thank everyone who has been replying to my questions. I'm new here and having a place like this to come to with my questions is really awesome. Everyone here seems nice and wise in the ways of these topics. Thanks.

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                • #9
                  Originally posted by Telos
                  Ok, I attached a wire to my case via one of the screws that holds the PSU in the case and ran the wire up to where the inverter is grounded. Almost all of the noise was eliminated. Now background noise can only be heard if I turn the volume up really loud (so loud that I probably would never turn it up this loud due to fear of blowing my speakers out). I may go out this weekend and buy a noise filter thing from radioshack or somewhere to get rid of the rest of the noise.

                  I want to thank everyone who has been replying to my questions. I'm new here and having a place like this to come to with my questions is really awesome. Everyone here seems nice and wise in the ways of these topics. Thanks.

                  In the past, I have found that more than 99% of noise can be elminated by using a single ground point for all the componenets in the audio path. Its sounds ugly, but in extreme cases, I have even solved it by securing a decent size ground wire from the chassis of the radio and connecting it to the same grounding point as the amplifier.

                  Most of the time you hear "Use a short ground" is to eliminate resistance in the ground lead from causing a (ever so slight) voltage drop in the reference ground of the unit. That is why you always want at least the same gauge ground wire as the power wire, and a common grounding point. By using multiple points to ground to along the chassis of the car, the resistance in the chassis of the car itself (It is a conductor, but does have resistance) can cause a slight voltage difference (aggravated by accessories like headlights, wipers, turn signals, etc) and throw any audio equipment's ground reference out of whack. Also, make sure you amplifier's chassis is not screwed directly to the metal of the car. There can be enough of a voltage difference from the point it is grounded to the point it is mounted to throw to reference off.

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                  • #10
                    Just personal experience: have m10000 via, with on board sound:
                    grounding case: 75% removal of noise
                    using a $13.00 ground loop isolator from walmart: another 20% removal

                    And that's with a wired FM transmitter

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                    • #11
                      using a $13.00 ground loop isolator from walmart: another 20% removal

                      Is that what they are called? I have a horrendous buzzing from my set up, grounding the PC case to my inverter helped tone it down a bit (from unbearable to very very annoying)

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