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Thread: The quest for no noise

  1. #21
    Variable Bitrate
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    Jul 1999
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    Greensboro NC
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    Post

    AaronCake: You'd be amazed at the number of trucks they drive off the assembly line (and I do mean drive) with big red tags reading "Warning: No Brakes"

    Most of the trucks from this plant spend more time before there shipped out, in the maintence shop than they do on the assembly line, and with that kind of rate you can imagine how many problems end up driving out the door unnoticed.

    Catlas

    P.S. Just makes you feel safe to be on the road doesnt it?

  2. #22
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    Oct 2000
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    Bakersfield, CA USA
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    Cool

    Rifken and all,

    I know no fighting we are all here to help each other.

    Okay a couple of things I would like to share. I have since done another install so this makes a big total of two for me now.

    Upon the first install on my Tahoe I had just a little bit of an alternator whine when the engine was running and nothing when the engine was not. The solution for me at the time was to install a Radio Shack 20 amp noise suppressor that solved the problem for me.

    Note: Just today I did rewire the Tahoe so that the audio and video wires were separated to the other side of the vehicle. I did remove the Radio Shack noise suppressor and I still had that same whine. So for now the suppressor is here to stay until I can figure what to do next. Now one thing that might be having an effect on the Tahoe is the fact that I have a dual battery system with a battery isolator so it is possible that it has something to do with it as well. I will keep everyone posted.

    The second install I have completed is in a 2000 Toyota Corolla. This install consists of the computer and a radio with audio inputs and a ten key keypad again with an inverter. This car had a major hum with and without the engine running. I noticed that if I grounded the computer to the car chassis that about 70% of the noise disappeared. So off again to the local Radio Shack. This time I purchased a ground loop isolator that goes inline with the RCA plugs from the computer to the car Radio. This also solved a portion about 90% of the noise disappeared so I thought okay well lets ground the computer to the chassis again and walla I would say that 100% of the noise is gone at least to my ears I hear 0 noise.

    What I would like to know and please forgive me if this has been answered previously is what causes ground loop. The only thing that I can think of is that the inverter when converting the DC to AC produces the problem. What I am not understanding is why this happens in the Toyota but not the Tahoe.

    I have a lot to learn but I am having fun doing it.


    ------------------
    MP3 - DVD - GPS
    Chevy Tahoe

    [This message has been edited by Tekati (edited 11-05-2000).]
    MP3 - DVD - GPS
    Chevy Tahoe

  3. #23
    Bj
    Bj is offline
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    Aug 2000
    Location
    Perth W.A Australia
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    Noise, oh noise. I'm an electronics engineer by trade, and a lot of my jobs require fixing ground loops in audio systems.

    The reason an inverter causes noise is because it has a transformer in it. This isolates the 12V side of the inverter from the mains voltage (240 or 110V) side. So neither the active or neutral of the inverter's power socket are tied to ground (or negative of your car).
    The AT/X PSU also has a transformer in it which isolates the mains voltage side from the computer voltage side.

    So when you hook it up to your puter power supply, you get a double isolated effect, which means your 12V car ground is now two transformers away from your computer ground.

    By connecting a wire from the car 12V ground directly to the motherboard ground, you bypass all of the isolation and the car 12V ground is now the same as the computer ground.

    Now what you have is the equivelent to a DC DC power supply where the grounds are at the same potential.

    However this can still cause ground loop noise because the amplfier in your head unit, (or sub amp bolted in your boot) also suffers from this same effect. Because your amp has the same ground as your mp3 player, and they are not tied to the same ground point, you get a voltage potential across the ground wires which will be induced into the audio section of your head unit amp.

    The ONLY way to stop hum (either on DC DC or Inverter) is to isolate the RCA's from your sound card to the head unit input. The Kenwood head unit I have has isolated aux inputs already, so there is no hum, but If your's isn't isolated you will need a ground loop isolator.

    Putting a HUGE supressor on your positive rail isn't going to stop it, as the noise from your altenator or igntion is only induced into your car stereo because It shares the same audio ground as it's power ground. By isolating these, you fix the problem.

    Good amps like Alpine, have isolated audio inputs already to prevent this problem. That's why you won't get hum using a tape adaptor, as it's an isolated input.

    The moral of the story is.............

    ISOLATE YOUR AUDIO GROUNDS FROM YOUR POWER GROUNDS.
    BjBlaster! Car MP3 & Carputer!
    bjblaster.com

    "The solution to one problem is only the beginning of another"

  4. #24
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    Feb 2007
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    fantastic post....

  5. #25
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    Mar 2004
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    holy crap batman!

    this has to be the oldest revival of a thread I've ever seen on this forum....and all to post "fantastic post"?

    amazing!
    Jan Bennett
    FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

    Please post on the forums! Chances are, someone else has or will have the same questions as you!

  6. #26
    Constant Bitrate
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    "What's old is new again", so they say.
    "It's a blessing . . . and a curse."

  7. #27
    Maximum Bitrate LinuxRacr's Avatar
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    I'm glad someone revived this, as it is just the stuff I need to read to fix my alternator whine issue...
    My Car: 2001 Mazda MP3
    My OLD Carputer project: Here
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    Current build! Here
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