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Thread: What all needs to be grounded???

  1. #1
    Variable Bitrate
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    Aug 2003
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    375

    Exclamation What all needs to be grounded???

    Ok, here's my setup:

    Car Battery -> (+) Distro Block -> ITPS -> PC -> (-) Distro Block -> Chassis
    Car Battery -> (+) Distro Block -> Amp -> (-) Distro Block -> Chassis
    Car Battery -> Ignition -> Amp/ITPS Switched Turn-on

    Right now the distro blocks power both my ITPS and my Amp. I have one for + and one for -. Everything is grounded and powered off of the Distro Blocks.

    When my computer is ON (whether I'm playing music or not), I get noise - not too loud, but loud enough for me to hate. It's basically white noise aka system noise. When I use my keyboard or touchscreen it seems like it changes slightly.

    When my computer is OFF and unplugged from ITPS, but my Amp is ON, it still makes noise.

    When my Amp is ON, but I unplugged my RCA cables from my PC (OFF and unplugged anyways), it went away and is completely silent.

    So it seems somehow my PC is generating noise even when off. The only explanation I have for that is if it is not coming from the PC itself (don't know how it could, as it's on the amprack on not sitting on wires), would be:

    1. Coming from the +5v wire which I have plugged into the PC's PSU and running up front to my USB hub and slimline DVD, even though it is powere off at this time, it still could act as a "noise antenna"??? but I think since my PC was off, it is not connecting the +5v to the sound card, so how can sound "jump" across when the PC is not on?
    2. Coming from USB, Keyboard or VGA cables which also run through the door sills (although on opposite side from my 4awg power cable, but still there are other wires in there so it could be something else) up to the front as well.


    YOUR THOUGHTS?????? PLEASE HELP! FOR THE LOVE OF GOD!!!

    Thanks in advance,
    Kevin

  2. #2
    Newbie
    Join Date
    Jul 2004
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    Brazil
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    If it is white noise, it's probably the floor noise level of the sound board output. Check the Signal/Noise ratio (SNR) of the sound card (or on-board sound) - if it's less than about 86db, you will notice some white noise.

    Try to mute Line-In, CD-Audio and everything on the windows mixer except wave-out. A lot of times white noise comes through the line-in input.

    If you get squeaking sounds when there is hard-drive activity and stuff, it probably is interference in the sound card from within the computer. In that case, try another sound card...

    But I don't know why you get white noise with the computer off... Isn't it the alternator whine (varies with RPM)? If so, the cause may be ground loop, you can try to isolate the ground wire (shield) from the RCA cables on one side (either at the computer or at the amp side) to see if the noise lowers. You can try also to use better quality rca cables with better shields.

    Anyway, if you are willing to spend a little, get an USB sound "card" and an USB extension cable and put the sound card right next to the amp - that should solve all of the above problems and give you the best quality sound.

  3. #3
    Constant Bitrate jpelzer's Avatar
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    I know that when my +12 line got disconnected from the battery (the fuse physically cracked, doh!), my computer shut off (obviously) and then I got this ungodly aweful racket coming from the speakers... Basically, grounding the sound card (a usb dealie) without power caused a loop to form.

    Put I don't know about when your computer is on...

  4. #4
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    Quote Originally Posted by sq_geek
    Ok, here's my setup:

    When my computer is ON (whether I'm playing music or not), I get noise - not too loud, but loud enough for me to hate. It's basically white noise aka system noise. When I use my keyboard or touchscreen it seems like it changes slightly.

    When my computer is OFF and unplugged from ITPS, but my Amp is ON, it still makes noise.
    I have this same exact problem. I have an inverter, that goes to the PC PSU. No OPUS or anything like that. Once you plug all of that in, it makes noise from the soundcard, even when the PC is off, but the inverter is on. You can hear noise from the PSU when its plugged into the inverter. I've cleaned up the ground on the car chassis for the inverter, but it didn't seem to help.

    I'm beginning to think that there isn't any real smooth solution to this, other than to stop using the inverter to power my PC (I still need it for the LCD PSU), and use an OPUS, or get a USB soundcard, as it seems they are able to filter through the noise. The inverter and PC just don't get along as electrical devices, and I'm wondering if using an inverter to a PC is bad for it in the long run?

    This really ******* sucks to deal with, I've already spent a lot of money already, and simple plans should just work right... If I had no problems like this, I would have already been done with my carputer.

  5. #5
    Variable Bitrate
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    Aug 2003
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    Well, the inverter makes sense, and the other scenario about the sound card being grounded also makes sense, but in my case nothing is grounded..

    The sound card's SNR is 108db, so that's not it, anyways it's when it's off, not on.

    Anyways, I'm going to go through in the next day or so and unplug each component (keyboard, usb chain, vga, +5v power for usb, and itps power on signal wire, to see which it is.. clearly one of those is picking up engine noise and sending it through to my PC and into my amp...

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