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Thread: Engine noise... only from computer! help?

  1. #1
    Constant Bitrate Pseudo Nim's Avatar
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    Engine noise... only from computer! help?

    Hey all,

    I'm experiencing the ubiquitous engine noise problem. However, I know my system is fine b/c if I use a PDA or an iPod to play, there's no noise; as soon as I plug in the PC, things go bad.

    I've run a fatass 8ga ground wire from the PC to the chassis and another, thinner, ground cable as well. The two grounds may theoretically be bad, but it made no difference in sound when I hooked them up (I had it on while doing it).

    I've tried wrapping the PC in aluminum foil COMPLETELY to kill EM interference, but it made no difference. A long time ago (before I grounded everything - but as I mentioned, grounding seems to make no difference) I tried an external USB sound card - didn't make things better (was, in fact, worse).

    I'm totally lost for ideas. Anybody have any suggestions?

    Cheers,

    -pN
    Doko ni datte, hito wa tsunagatte iru...

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  2. #2
    Variable Bitrate numbers's Avatar
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    Sounds like most likely a ground loop isolator would make it go away.

  3. #3
    Constant Bitrate stapan's Avatar
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    Its either a ground loop or electromagnetic interference.

    here are solutions for each.

    ground loop-

    upgrade the vehicle grounds. start with the main negative cable from the battery. you want a good ground path from: the frame, the body, and the engine.

    upgrade/add the power supply ground and grounds for the amps (if any).

    important: where and how you ground makes a huge difference. the wire gauge is secondary. where did you ground? the floor pan is best; some parts of the chassis are just poor ground spots. make sure you grind the ground point on the body completely free of paint and anything else (it should be shiny metal). for cable, I like 1/0 welding cable from weldingsupply.com. alternatively, if in a bind, wal-mart sells cheap 2 and 4 gauge battery cable.

    make sure your ground cable connectors are securely crimped or soldered.

    emi-

    route your audio cables (most importantly, any RCA cables) away from any power cable, including any power cables for PC or amps. also try and route these away from EMI hot spots (other wiring like for a/c, radio, cig lighter, etc.) generally avoid locations with a lot of other wires.

    a ground loop isolator may work, also. but many of the above suggestions are completely free and would eliminate the real source of the problem. hth good luck

  4. #4
    Variable Bitrate numbers's Avatar
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    Upgrading grounds doesn't make ground loops go away. It upgrades them.

    The two problems mentioned are basically the same.... or I should say that they are related. Interference is the root problem. It's what causes the noise. When you have a ground loop, it makes it extremely likely for interference to be picked up. Thus, removing the ground loop won't always necessarily kill all the noise, but it very well may.

  5. #5
    Constant Bitrate stapan's Avatar
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    Quote Originally Posted by numbers
    Upgrading grounds doesn't make ground loops go away. It upgrades them.

    The two problems mentioned are basically the same.... or I should say that they are related. Interference is the root problem. It's what causes the noise. When you have a ground loop, it makes it extremely likely for interference to be picked up. Thus, removing the ground loop won't always necessarily kill all the noise, but it very well may.
    right... a bad ground isn't the most common source of noise or anything like that..

    oh yeah, and lets forget about differences in electrical potential too.. its all about INTERFERENCE

  6. #6
    lez
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    no point offereing suggestions just yet not enough information has been given.

    IE:

    PSU used

    wired to where

    audio used

    amp used

    how is audio/amp connected

    does engine rpm affect it.

    is it their with igniton off/onn/engine running

    type of noise
    Lez, more widely known as flez1966

  7. #7
    Variable Bitrate numbers's Avatar
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    Quote Originally Posted by stapan
    right... a bad ground isn't the most common source of noise or anything like that..

    oh yeah, and lets forget about differences in electrical potential too.. its all about INTERFERENCE
    You gave upgrading grounds as a fix for ground loops. It isn't. Simple as that. Bad grounds are another cause entirely. Lets try to keep the arguing to a minimum and the good information to a maximum. I'm not out to call bs on anyone. I'm just doing what I can to remove the sarcasm from "if I read it on the internet it must be true."

    Now having said all that... if you plug some headphones into the computer and don't get any noise, you can bet it's a ground loop. It probably is.

  8. #8
    lez
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    lol unless its a pc psu side ground loop!

    sorry couldnt resist.

    come on guys lighten up and lets help not squabble
    Lez, more widely known as flez1966

  9. #9
    Constant Bitrate Pseudo Nim's Avatar
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    Hey all - thanks for the suggestions. Just to give more info:

    PSU - M1-ATX
    Wired to: I split the wires coming from the car radio and ran the +12/+12switched from there along the center of the car together with the audio cables to the computer (see note about RCA cable routing below). Ground is to the car underbody, though I didn't sand the area.

    Amp has its own wiring (directly to battery) & RCA cables, routed separately from the computer RCA/power cables. Grounded to the same location as the PC.

    Noise/static is present with engine on, RPM makes it get worse; with engine off, still SOME noise is present: if I turn up the HU volume very high (60-70% and higher) I can hear hard drive access being echoed through the speakers and some random, though faint, crackling.

    Type of noise: high-pitched whine + some static (in case of hard drive, sounds more like crackling).

    Now re: wiring. I thought RCA routing might be an issue, but when I took a diff RCA cable (hard to take mine out, hehe), and just connected it to the PC->HU and held it up in the air, it had the same effect, the noise was not different in the slightest. Also like I said, if I use a non-grounded device like an iPod, there's *no* noise.

    Note 2: When I tested with the iPod, I had the computer ON, and used the RCA cable from the computer, so the path of the audio signal is EXACTLY the same as from the PC. I.e., I don't think it's EMI from the power wires.

    From what I'm hearing, a ground loop isolator is a band-aid fix, isn't it? I mean, my system itself has no problems, since everything EXCEPT the computer has no noise in it - the CD, external AUX devices, etc. Hence, the problem must be in the computer - what do I do with it, though?

    Cheers,

    -pN

    Quote Originally Posted by lez
    no point offereing suggestions just yet not enough information has been given.

    IE:

    PSU used

    wired to where

    audio used

    amp used

    how is audio/amp connected

    does engine rpm affect it.

    is it their with igniton off/onn/engine running

    type of noise
    Doko ni datte, hito wa tsunagatte iru...

    My BMW 335xi install
    My Subaru Impreza install (now retired...)
    Realtime audio freestyle hiphop battles online - www.letsbeef.com!

  10. #10
    Variable Bitrate numbers's Avatar
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    Sand those grounds. It's just good practice one way or the other.


    Plug some headphones into your computer and listen carefully because any noise will be much quieter on headphones than on amp'ed speakers. Any noise you hear in the headphones is probably noise that you will have to live with. If you don't hear the noise, then you will probably be able to get rid of it. The problem is not likely actually caused by your computer - just by the disagreement between your computer and amp. The short version of the story is that car audio manufacturers suck and can't get their **** straight so we have to have gain adjusters and ground loop isolators and whatnot to make everything play nice together. Some could argue that a ground loop isolator is a bandaid solution, but it is a necessary one. Think you can take out your sound card and figure out how to lift it's audio ground from it's power ground? Didn't think so. Even I haven't attempted that one. Unfortunately ground loop isolators are here to stay until manufacturers learn some common sense.

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