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Static Induced in 3.5 mm Audio Extension Cable

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  • Static Induced in 3.5 mm Audio Extension Cable

    Hi all,

    I'm currently putting my first carputer in, and things are actually going pretty smoothly. To get audio to my system, I've installed an equalizer/processor unit up front that takes RCA red/white connectors and then outputs RCA connectors to my amp. I split the audio coming from my onboard audio to an RCA cable. Things sound pretty good in the system until I introduce my 20 foot 3.5 mm audio extension cable. The carputer sits in the trunk and the equalizer/processor is up front, so I needed to run a cable from the carputer (trunk) to equalizer/processor (front). So long as there is music playing from the carputer, things sound decent. That silence between songs is filled with buzzing though. Even if I turn the volume on the equalizer/processor to 0, there is still buzzing. As soon as I disconnect the extension cable, the buzzing goes away at both high and low volumes. When I plug an iPod up to the equalizer/processor up front with a nice short cable things also work well without the buzz.

    Am I doomed to suffer from the buzz of a 20 foot cable? If I got a USB sound card and mounted that closer to the equalizer/processor might I have better luck? Should I mount the PC up front to keep those runs short? Any ideas I haven't thought of?


  • #2
    I'm a newbie, but you are using a thick cable(like home theater RCA type), I guess it should have better shielding.
    did you run this cable next to some power cables? maybe you can try re-routing this cable, see if it helps.
    I would try grounding the cable too, maybe it would help(outside metal sleeve of the cable to chasy of the car).


    • #3
      I'd get a quality shielded 3.5 to RCA cable, and make sure you don't run it (or any audio cables) next to your power cables.
      1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.


      • #4
        it's called a ground loop

        you have 2 devices drawing power from 2 different sources with different ground potentials, and the audio cable is connecting the 2, causing the hum, as the device with the higher ground potential tries to use the audio cable for a ground....

        there are tons of guides all over on how to trouble shoot this(i have replied to a ton of threads on here, and i think there is a sticky as well, not to mention all the car audio sites that also go over it)-- check those, and let us know how it works out
        My OLD 2001 Mitsubishi Eclipse GT:
        "The Project That Never Ended, until it did"

        next project? subaru brz
        carpc undecided


        • #5
          Winner goes to ground loop. I plugged in an ipod and got static free musical entertainment. Along the way, I found out some fun FYI's:

          1.) Even when I ran the audio cable outside of the car (I had 20 feet of it), the static was still there. Gave me a hint that the problem wasn't completely related to proximity to power lines.
          2.) When I selected the other input on my equalizer (with nothing connected to the other input) I could turn the volume all the way up and hear the music in the static. Kind of cool. Really weird.
          3.) The ground for my PC isn't making the best connection with the chasis. When I wiggle it around the static pops and sometimes goes away.

          Oddly, during testing, I disconnected the audio cable from my computer, plugged in some different cables to test quality issues, and replugged the audio into my computer. There was no sound coming from the computer and my lilliput up front started freaking out and scrolling wildly, before selecting a non-existant file on my computer. I quickly turned off the car to try and prevent any permanent damage, and when I rebooted, the audio was SUPER faint. I checked all the cables. All plugged in. Checked all the audio options (that I could think of) on the board. All turned up. Somehow my audio has now been cut to a slim picking of what it used to be. I'm running Centrafuse, and when I re conducted the experiment, the audio paused iPod style when the cable was disconnected, and when I put the cable back in Centrafuse said it was playing the song, but the track timer wasn't progressing. Pressing pause and play didn't help, so a quick restart of Centrafuse got the song playing again, but still at super low volume. I think I might have upset the poor onboard audio. I'll be bench testing the rig tonight to see if I can't get it working, but it's a little disconcerting that I might have fried a board so easily.

          Moral of the story, I'll be reattaching my ground for my PC, but also will probably be looking into an external or at least PCI based sound card. The mobo sound might just not cut it.

          Thanks for the help.

          Suggestions are always welcome


          • #6
            another solution if reattaching the ground doesn't fix it:

            I'm going to be running my audio wiring to and from the amp in the trunk of my car so what I plan to do for optimal shielding is use the existing ground points along the wire path and strip the insulation from the ground wires to make contact with either aluminum tape, or foil covered by electrical tape. This will provide a consistent ground along your audio path, won't require the purchase of new, expensive wiring, or a needless soundcard.

            for clarification: I'm adding new ground wires to each ground point and stripping insulation from THEM, not hacking up the existing wires.


            • #7
              maybe it would be a good idea to use video component cable or digital coax cable from monoprice. they should have much better shielding.


              • #8
                The shielding doesn't help for ground loops.

                One solution is to break the shield at one end - usually the target end - but that's covered in ground loop solutions.


                • #9
                  Buy a cheap USB sound card. Trust me I am very experienced in killing ground noise in a vehicles audio system and sometimes you just can't kill the ground noise only mitigate it to where it is barley noticeable. When the situation arises that calls for noise free setup I resort to a USB sound card. USB sound cards are purely digital and use a digital to analog converter to convert the audio signal for use by more traditional audio setups. If you take this approach it will exclude the PC as a ground noise culprit. This will though not eliminate other sources of ground noise.


                  • #10
                    Just to update everyone:

                    The biggest point of noise in my system was actually my m4 power supply. It was a junker, and I picked up an Opus that works significantly better. All the suggestions in this thread were hugely useful (most importantly the SOLID ground connection), but check that power supply if you are still getting weird noise. It was the key for me.

                    Happy carputing everyone


                    • #11
                      Not unsual...

                      Fairly well described in power supplies with minimal radio interferance? especially by Mickz in later pages.


                      • #12
                        good to know you got it figured out! thanks for updating the thread.
                        My OLD 2001 Mitsubishi Eclipse GT:
                        "The Project That Never Ended, until it did"

                        next project? subaru brz
                        carpc undecided