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  • noise investigation

    After wiring everything into my vehicle, there is noise which I anticipated. Right now I need to investigate where my noise is coming from. Here is what I have right now:

    2 OPUS with 8 gauge wire right from the Battery
    a ignition control wire turn on the power inverter and trigger the OPUS
    a common ground in the trunk where i grounded EVERYTHING together

    Right now I am using TV out from my carputer. The RCA goes into a AV switcher, which then go to my headunit and other LCD screens. Other components connected to the AV box includes a PS2, and a VCR.

    If I connect my computer through the AV box, I get alternator whine. If I bypass the AV box and go straight from computer to headunit it has no noise. So I am sure it is not the RCA cable that is picking up the noise.
    Also since I get no noise with just the computer and headunit, I am sure it is not my computer making the noise.

    So I guess it is my AV switcher that is causing the noise ?

    Here is how my electrical system is wired. One opus feed power to the computer, and the other OPUS feed power to the AV switcher, two video amp, and 2 Xenarc 7" LCD. They all have the same 12v source and same ground. Is there any way i could try to stop the AV switcher from picking up noise ?

    Another thing I tried is to put a ground loop isolator between my AV switcher and headunit and that didn't help either.

    Anyone know what my problem is ? Any solution ? Could it be a bad AV switcher ?
    Honda Lagreat Carputer Project. Mobile Entertainment
    http://www.mp3car.com/vbulletin/showthread.php?t=33936

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  • #2
    Well the only way you get elecrical noise is through the RCA's or them being cheap and unsheilded.you must have some of the RCAs to close to one or more power sources.
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    • #3
      All the RCA are monster cable which are not cheap. With the same cable all at the same location, when I plug it into the AV switcher it has noise and when I just use a connector to connect both cable together it has no noise.

      If the RCA are picking up noise, then shoudln't there still be noise whether I plug it through the AV switcher or not ? mind you that the cable are exactly where they are as I did not move them.

      That's why I believe it's not the RCA.

      edit: I just used a ground loop isolator in between the computer and AV switcher, all noise are gone. What does this mean ? Does it mean it's the cable from my computer to AV switcher picking up noise ? bad ground ? or what ? I am trying to fix the problem thus not having to use a ground loop isolator.
      Honda Lagreat Carputer Project. Mobile Entertainment
      http://www.mp3car.com/vbulletin/showthread.php?t=33936

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      • #4
        Can you try using one Opus for the PC and AV (this might mean not using any screens or other components) to eliminate the possibility that the Opus' are causing it. Ground loops are a pain to track down.

        Did you also try and put the ground loop isolator between your PC and your AV?

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        • #5
          Ground loop may not be the issue here. What you need to look for is.


          1. Your audi cables should be at least 10" away from your power cable.

          2. VIDEO AND USB CABLES GENERATE A LOT OF NOISE!!! Watch out. If you run them next to your audio cables it could be a problem.

          3. Try to disconect your components one by one to find out where the problem is coming from.

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          • #6
            I don't think it is the OPUS. At first I only used one OPUS for the computer and the car's power for other video components. It created the same noise with the AV box and none without it.

            I moved the AV box front the front of the vehicle to the trunk with all new wiring to the OPUS. Same noise with the AV box and none with it.

            One funny one is that when I plug in other source such as VCR and PS2 into the AV box it doesn't have alternator whine. There is only alternator whine when I switch it to computer. However if I bypass the AV box and go from AV box straight to headunit there is no noise AT ALL.

            I got a noise filter from radio shack and hooked it up to the AV box, no change.

            Right now I have a ground loop isolator between the computer and AV box, which eliminated ALL the noise.

            What might cause the problem? Is it my computer actaully making noise? But there are no noise from compute to headunit. I am really confused here. I have tried everything I read on the forum such as grounding the case, psu, motherboard, sound card,,etc etc etc etc and still no use.
            Honda Lagreat Carputer Project. Mobile Entertainment
            http://www.mp3car.com/vbulletin/showthread.php?t=33936

            Full Spec for mods check out:
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            • #7
              People have a pretty poor misconception about noise radiating into RCA cables and in the greater majority of the cases it just doesn't happen. It especially doesn't happen to the point where alternator whine is prevalent at low volumes like what happens with a ground loop (which is a direct injection of noise).

              There is a mismatch between your PC and the AV unit which the ground loop isolator fixed but tracking down the true source of this can sometimes be a pretty tricky task.

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              • #8
                I've got some bad alternator noise

                Noise, on everything. I have a head unit going with 5 rca's to a 5 channel amp. i have noise on the pc, the radio or the cd. I am sure this is a ground loop. How the heck am i supposed to fix this>? Should I ground the head unit at the place the amp is grounded? I get mixed versions of what a ground loop is. Can anyone explain in laymans terms? THanks.

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                • #9
                  Originally posted by lookinco
                  After wiring everything into my vehicle, there is noise which I anticipated. Right now I need to investigate where my noise is coming from. Here is what I have right now...........
                  I would try powering the av switcher with the same PSU ( because of the ground) that powers the sound source.

                  check this: http://www.mp3car.com/vbulletin/show...613#post274613
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                  • #10
                    ^ Did you read the thread at all? I already mentioned that and he said he tried it and it didn't help. He also mentioned a ground loop iso between the PC and AV fixed it.

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                    • #11
                      Originally posted by MrPerfectionest
                      ^ Did you read the thread at all? I already mentioned that and he said he tried it and it didn't help.
                      Yes I did, and just to be sure, I read it all again. He never said that he had the av switcher and the pc powered by the same source.

                      Originally posted by lookinco
                      One opus feed power to the computer, and the other OPUS feed power to the AV switcher,
                      One in each OPUS

                      Originally posted by lookinco
                      I don't think it is the OPUS. At first I only used one OPUS for the computer and the car's power for other video components. It created the same noise with the AV box and none without it.
                      One in the Opus and other directly to bat.

                      Originally posted by MrPerfectionest
                      ... He also mentioned a ground loop iso between the PC and AV fixed it.
                      Yes, but he also said:

                      Originally posted by lookinco
                      Right now I have a ground loop isolator between the computer and AV box, which eliminated ALL the noise.

                      What might cause the problem? Is it my computer actaully making noise? But there are no noise from compute to headunit. I am really confused here. I have tried everything I read on the forum such as grounding the case, psu, motherboard, sound card,,etc etc etc etc and still no use.
                      Witch I presume means that he is curious enough to try to find the real problem.

                      My sugestion is that till now, is PC had two grounds. One from the rca connector on the AV Switcher and other from the Opus. Thats why the ground loop isolator only solved the problem when between the computer and AV box.
                      Ikea Case. Epia M10000.M1-ATX. 512 Mb. 2,5" 80 GB HDD. 7" Lilliput. BU-303 GPS. Sony Joystick.
                      Status -->
                      Lilliput Installed (not indash yet..)
                      BraveCar 2.5

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                      • #12
                        Do you have another AV unit that you could use to test to see if it is AV Switcher. I know that you said that other componants work the AV Box but it is worth a try.

                        Try grounding things in a different location.

                        Try unplugging all inputs from the AV box and take the RCA from the computer and touch the chassis of the AV Box. If you hear the noise then it is comming from your computer.

                        Check the ground on your computer. Is the computer in a metal case. Ground the computer to your PS if not. The best ground location on the via is the screw hole next to the PS/2 connectors.
                        -Jesus- King of Kings Lord of Lords

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                        • #13
                          Thanks for everyone's input. Everything has the same ground point. The two OPUS, computer case, AV switcher, inverter, all the screens. I rewired everything to the same ground point and 12v source. One OPUS for the computer, one OPUS for AV parts. Both OPUS get the same 12v source, same trigger, and same ground.

                          I tried to plug sources into the headunit and into the AV switcher, they all make NO noise at all. The only time I have noise is when I have my computer go through the AV switch into the headunit. If I bypass the AV switch then there is no noise also.

                          Like I said right now I have ground loop isolator in between the PC and AV switcher which eliminated all the noise. So my guess is the noise IS coming from the computer.

                          I will try to ground more things to see if it eliminates the problem. My system is a Shuttle in a shuttle case with a OPUS for shuttle and another OPUS secured on top of the shuttle case. I have tried grounding the case by attaching a groun wire to one of the case screw, but that didn't help.

                          Still confused...
                          Honda Lagreat Carputer Project. Mobile Entertainment
                          http://www.mp3car.com/vbulletin/showthread.php?t=33936

                          Full Spec for mods check out:
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                          • #14
                            It is possible that your AV switch is actually picking up the noise comming from another source through the ground wire attached to the AV switch. You say that when you bypass the AV switch, you get no noise, right? I would check your vehicle for loose ground straps. You van will have several. They usually attach from the engine/trans. to the body and frame, and also from frame to body. 1 of them may be loose, have fallen off, or has corrosion and making poor contact. Another thing to think about is the length of the ground wires you currently have. Shorter, the better. If you have too many ground wires running all over just to tie them together, this could cause problems too. Each electrical device you add to your vehicle should have it's own ground wire, of a decent gauge size, and be as short as possible (under 24" is prefered).

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                            • #15
                              I have tried the AV switch with just the computer plugged in. Before I rewired everything, there actaully was noise coming from other sourceand some static on the video. However after I rewired everything that problem was gone.

                              The AV switcher is right beside my computer which is right beside my ground point. The ground wires is 8 gauge and is less then 2 feet long.

                              I will check the ground strap tomorrow.
                              Honda Lagreat Carputer Project. Mobile Entertainment
                              http://www.mp3car.com/vbulletin/showthread.php?t=33936

                              Full Spec for mods check out:
                              http://www.hondashowoff.com/profile.php?id=3766

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