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Thread: The hiss of death... damn you electricity!

  1. #1
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    The hiss of death... damn you electricity!

    Hello All,

    Thanks to anyone for their time in responding to my questions. I am in about month two of my carpc project. Had everything put together but not permanently so (car is still torn apart) in case I needed to revise anything. Good thing I left it this way because I am experiencing some awful hiss and whine. I put in a ground loop isolator between the sound card and amp and it made it tolerable but was still getting major hiss before windows started and minor hiss afterwards. I went out and bought a new sound card hoping it would cure the hiss before windows but no dice. To further troubleshoot I hav disconnected just about everything now and as a test used an old school iriver h300 with line out and the audio sounded crisp and clear, no engine whine or hiss.

    I have the below equipment:

    2010 vw golf 2.5
    quad 7850 amp
    zotac intel culv mobo
    creative 5.1 usb sound card
    16&14 gauge wire throughout the car
    m3-atx 90 watt ps
    scc1 sirius sat radio
    mini touch 700 screen


    1.) I have read that ground cables are only supposed to be about two feet but are all supposed to go to the same point, since for most installs these seem to be contradictory are most setups not grounded properly?

    2.) What is the best way to splice multiple cables together, solder and electric tape? Those snap in multi connectors or something else?

    3.) Does the gauge of wire matter for the ground? Will too heavy of a gauge cause it not to work as well?

    4.) I currently have two power wire one is constant 12v ignition off or on and the other is only 12 v when ignition is on. I am running the lcd screen and comp off the constant 12v and the amp and sat radio on the switched 12v. Anyone see any problems with this?


    5.) Should all of the below have a separate ground that goes to the same point (battery terminal?)
    Mobo (grounded by power supply?)
    case ?
    audio cables?
    lcd screen?
    amplifier? (has a slot for the ground wire)

  2. #2
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    Since I connected the mp3 player and was able to get clear sound I think it's safe to say the issue is coming from the PC. Whether it be because it is grounded poorly or because the psu is putting out a lot of noise. I am going to try powering the pc tonight via and ac connection outside of the car and hopefully will tell me if the issue is from the power going to the pc or maybe a grounding issue.

  3. #3
    Constant Bitrate kolton5543's Avatar
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    Seems like it is a very bad ground loop. Maybe the ground loop isolator is a lemon or just not of good quality. Also, yes, the size if the ground wire does matter. No, it cant really be too big. Remember. Your power can only be as good as your ground.

  4. #4
    Newbie jontheinstaller's Avatar
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    Run a ground wire to your Rca on the PC and see if it goes away

  5. #5
    And then I was mod. Tidder's Avatar
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    Quote Originally Posted by jontheinstaller View Post
    Run a ground wire to your Rca on the PC and see if it goes away
    My thoughts exactly. All 3 of my installs have had electrical noise fixed by grounding the audio ground to the car somewhere. Ground loop isolators are shoddy at best, I've never had one work for me.
    Tidder

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  6. #6
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    Quote Originally Posted by Tidder View Post
    My thoughts exactly. All 3 of my installs have had electrical noise fixed by grounding the audio ground to the car somewhere. Ground loop isolators are shoddy at best, I've never had one work for me.


    Tiddler,

    With your grounds were they grounded all to the same point or to different good grounds? I have sanded down the paint in the middle "backbone" of the car and was connecting a ground there but only got more noise when the isolator was connected and only a little less without the isolator.

  7. #7
    And then I was mod. Tidder's Avatar
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    Sorry for the late response. My first install all my grounds were to different points. My last install, all my grounds in the trunk were to the same point. Amp ground and CarPC psu ground were the same. I actually ended up grounding my audio ground to the casing of my head unit after trying to ground it in the trunk to the same point and having audio noise. I would suggest just experimenting as much as you can. It doesn't seem like there is one answer that fits all.
    Tidder

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  8. #8
    FLAC PhilG's Avatar
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    I am running the same sound card as you are and I have no noise issues when levels on the PC are all maxed out and volume is controlled within the audio system. I have experienced some significant hiss and pops when the PC volumes are turned down which I assume it's caused by a poor S/N ratio when the PC is outputting too low of "pre-out" voltage. So I'm not sure how you would accomplish leaving the PC volume high without some kind of hardware after the PC to attenuate the volume but that is my experience.

    I have also experienced a couple of times where the "line in" which the SAT radio is connected to has not muted and noise from the SAT radio translator has created some interesting sounds. I have no idea what was happening in those instances but unplugging the sat radio 3.5mm plug from the X-fi card eliminated the noise at that time.
    I have never had any form of alternator whine, just hissing in certain instances.
    My 2007 Ford F350 Work Log located HERE

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