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  • Sound Feedback Issues

    Hello,
    I apologize in advance if this is the wrong section, but my question sounds like a newbie one to me. This is my first project so i thought i would show what I've done and ask for help. The car is a fully built 93 mazda miata turbo. Here are my specs so you know what your advising on:

    Specs:

    Jetway C7 mobo 1.5 ghz
    M1-ATX PSU w/ startup-shutdown controller
    Low profile case
    RAM - Kingston DDR2-533
    a 40 gb laptop drive
    Xenarc 7" touch screen

    Now I installed the PC and it runs fine.. sound is run through a 1/8" to RCA split into my headunit. I am experiencing awful feedback from the PC at this point. I thought possibly this was a grounding issue so I checked all grounds. My main power and ground are coming from the battery, with the acc off my fuel pump line. I have also grounded the case and the metal "mounting board" inside the case to the car body (seat bolt). I have been experimenting by only "partially" putting in the 1/8" creating a "mono" effect, and this completely removes the feedback. Is this an onboard sound issue? I have read multiple threads on "ground" loop, but I believe I certainly grounded properly. Any help would be useful. I will be going to radio shack to attempt the "ground loop isolator" tomorrow.

    Pic of my installed product fiberglassed into the dash:


    The PC:


    Here is the car:


    1.63L - GT2871 - MegaSquirt- ~2k lbs.

  • #2
    acc off the fuel pump is probably a problem. why not use the one from your radio harness?

    Comment


    • #3
      You call it feedback, but it sounds like some other type of oscillation. Possibly some kind of missmatch between yr HU and computer audio out.

      I had a hiss in my system only on one of the amps, so I did buy the Radio Shack grnd loop isol. It worked perfectly, and I did an exhaustive A/B test to determine if insertion of the isol affected my audio quality - no degradation that I could hear...

      Seat bolt grounds are a no-no. There is paint, grease, undercoating, sound deadening material on, around, and under those bolts. I suggest that you could drill another hole near the seat bolt if it works best for you - make sure that you grind the area very well to the bare metal before mounting the bolt. Do your best. Now you have a wonderful excuse to buy a Dremel tool with all those neat little attachments...

      Sometimes "over-grounding", by putting grounds to everything in sight to different grounding points can create a voltage differential between grounds - a ground loop. Maybe remove some grounds, leave only the basic ones.

      best of luck and blessings.
      Happy CarPC'ing!

      Comment


      • #4
        Couple things to try:

        Get that acc off the fuel pump motor line!

        Anything that is attached to a running motor of any kind will be "noisy". It may just be an acc line, but noise can enter into a system in a multitude of ways.

        Grounds:

        Try to run them to a common ground. Grounding the case is a good idea, just make sure it's a good ground.

        Try grounding your RCA's. just jumper a wire to ground from the shell for now.

        A ground loop isolator may work, but you will loose sound quality as a result. If a GLI can remove the noise, ou can alos remove it by proper grounding. Sometimes just moving the ground a few inches fixes the issue. You have to experiment a bit.

        You also have to be carefult to route RCA's away from potential noise sources such as power wires and electric motors. If you must cross power wires, do it at a 90 degree angle.

        Power and signal wires should never be run parallel due to induced voltage/current concerns.

        Volume:

        Since you're running the volume into a head unit, you have a multitude of volume controls, from winamp (or whatever media player you're using), system volume and HU volume. If you have the sytem volume turned way up and then turn up the HU volume, you'll be amplifying noise as well as music. Try your system volume at no more than half and then turn up the HU to see if the noise is still a problem. Try a couple different combinations between the volume controls.

        9 times out of 10, this kind of problem lies in the install itself though.......

        Good luck
        For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.
        Leonardo Da Vinci

        Comment


        • #5
          I respect what the car audiophiles say about GLI's, but I'm tellin' you - I listened carefully and there was zero change in audio quailty after inserting GLI.

          Perhaps there's an unheard, but nevertheless important audio quality that GLI's remove or interfere with. If so, being in a science field, I'd be interested in evidence of problems cause by GLI's...maybe in another thread.
          Happy CarPC'ing!

          Comment


          • #6
            Originally posted by brucedog View Post
            ..

            Seat bolt grounds are a no-no. There is paint, grease, undercoating, sound deadening material on, around, and under those bolts. I suggest that you could drill another hole near the seat bolt if it works best for you - make sure that you grind the area very well to the bare metal before mounting the bolt. Do your best. Now you have a wonderful excuse to buy a Dremel tool with all those neat little attachments...
            The car is completely gutted, it is a track car w/ 300 rwhp The grounds are on solid metal that I sanded with the air grinder.

            Originally posted by greatwhite View Post
            Couple things to try:

            Get that acc off the fuel pump motor line!
            ..
            Since you're running the volume into a head unit, you have a multitude of volume controls, from winamp (or whatever media player you're using), system volume and HU volume. If you have the sytem volume turned way up and then turn up the HU volume, you'll be amplifying noise as well as music. Try your system volume at no more than half and then turn up the HU to see if the noise is still a problem. Try a couple different combinations between the volume controls.

            Good luck
            I relocated the acc to the stero acc line... no dice. I then went out to radio shack and picked up a GLI. I ran out of patience for the day since I had my damn 4 hr CISSP examp today. I am not overly concerned with the sound quality, the car is superloud and it would just be nice to be able to hear the music without feedback I will brief on the GLI after the install.
            1.63L - GT2871 - MegaSquirt- ~2k lbs.

            Comment


            • #7
              Originally posted by brucedog View Post
              I respect what the car audiophiles say about GLI's, but I'm tellin' you - I listened carefully and there was zero change in audio quailty after inserting GLI.

              Perhaps there's an unheard, but nevertheless important audio quality that GLI's remove or interfere with. If so, being in a science field, I'd be interested in evidence of problems cause by GLI's...maybe in another thread.
              I agree. I have a high output alternator that always seems to cause noise. I used GLIs from Best Buy. The manufatuer is called Install Edge, and they guarantee that there will be no loss of sound and a 3db gain. I use one for the front, rear and sub with no issues at all. Sound quality is not affected at all! So if you go with a good GLI, its all gravy. If you go with a cheapy from RadioShack, well there are no quarantees.
              Nirwana Project, the Android/Win 7 hybrid system!

              1X Ainol Novo Flame Tab
              4X MK808b
              3x Perixx Touchpads
              3x 7 inch Screens
              1X 7 inch motorized Screen
              1x Win 7 PC

              Comment


              • #8
                GLI from radio shack installed... noise is now gone! Great advice!
                1.63L - GT2871 - MegaSquirt- ~2k lbs.

                Comment

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