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Thread: Fixed Ground, How to fix screech?

  1. #1
    Newbie Red_Beard's Avatar
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    Fixed Ground, How to fix screech?

    I just fixed my ground loop problem. Grounded it straight to the chassis. No more alternator whine.

    Now, I've had this problem all the while, its a little more peculiar. This sound starts approximately when the mini gets to mac os x. Its a sorta screech. Does NOT change with engine speed. Never changes. Sometimes goes out then comes back. Really unsure what this is.
    Any idea?

  2. #2
    Fusion Brain Creator 2k1Toaster's Avatar
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    does it go away if you mute the music, or does it remain?
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  3. #3
    Newbie Red_Beard's Avatar
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    Mute the music on the Mac, yes.

    Oh, forgot to mention.
    When I detach the monster cable to the mac mini it stops.
    If I hook that same cable up to a ipod or mp3 player, sounds better than the mac mini, no noises.

  4. #4
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    try running another cable directly to your amps, outside of the car, then to the mini. This will tell you if its the cable. It could be a bad cable or just bad routing through the car.

  5. #5
    Newbie Red_Beard's Avatar
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    I don't have any amps hooked up at this point.
    Bad routing? What would you say bad routing would be? I didn't do the GREATEST job routing it. It just gets there.

    My cable, hm possibly. My positive line is a little iffy now that I think of it.

    I couldn't buy any 16ga wire from the Shack so I bought 12ga. Here's the setup basically:

    Code:
    +     -  positive terminal
    --    -  16ga wire
    //    -  the fuse
    ==    -  12ga wire
    [ ]   -  the unit
    
    
    +---//=========-----[   ]
    so it goes from 16ga to the fuse, up to 12ga, then when it gets close to the unit, it goes back to 16ga. You think this could be it?

  6. #6
    CarFrontEnd Creator iamgnat's Avatar
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    Is that wiring from the battery to the power supply?

    If so, 12ga wire is not nearly enough. You should be running 8ga at a minimum. Anything less is running the risk of a fire hazard. Since you are talking Radio Shack for the wire, I assume you are using from fuse from them to? Nothing from them is fit to be in the engine bay of your car. If this is really the PSU wiring you have set up you need to go disconnect it and go have a good Car Audio shop rewire it for you.

    -dave
    My pathetic worklog.
    CarFrontEnd (now it's own sub-forum!!!!)

  7. #7
    Newbie Red_Beard's Avatar
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    Even for the CarNetix P1900? It comes with 2 16ga positive inputs, so I figured it can only accept that much input.

  8. #8
    Newbie Red_Beard's Avatar
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    From the CarNetix Manual:
    Attached Images Attached Images  

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    I mean the actual monster cable audio cable.

    To troubleshoot any audio problem just follow the flow of the system.
    1st test the source, hook up a pair of computer speakers to the computer's output. do you have the noise now? If yes, then the problem lies within your computer, either swap the computer or try to use a different audio output. USB audio outs are not that expensive, you could try one of those if the computer is the problem.

    2nd. if the noise is gone when you listen through the computer speakers then the computer is good, so test the audio cable. Run a different audio cable from the computer to wherever the other end of that monster cable goes. just run it loose and not tucked in to the car. If you have noise with the new cable then your monster cable is probably not the problem. If the noise goes away, try running the temporary cable alongside the the monster cable and see what happens. If the noise comes back then, you should seek out a different path through the car from the computer to the destination and your monster cable is probably okay.

    If the noise is still there in the temporary audio cable, then the sound is entering the system after the Monster Cable. What is the monster cable running to?

    The things you describe with your positive cable shouldnt' have anythign to do with this noise if you can still hear the noise using an ipod since the ipod is not powered off of that line, but I agree with Dave on his recommendations.


    Let us know.

  10. #10
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    Quote Originally Posted by Red_Beard View Post
    Even for the CarNetix P1900? It comes with 2 16ga positive inputs, so I figured it can only accept that much input.
    You could have power cables the size of your thumb, a piece of gear will only pull as much power as it needs. Think of it as if you had different glasses in front of you that were full of water and each had a different size straw in it. The smallest one would probably not get the job done, but having a straw that supplied more water than you need wouldn't drown you, you only drink as much as you want. It's a flawed example but I'm too tired to be creative.

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