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Thread: few questions

  1. #1
    Newbie
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    Dec 2010
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    few questions

    Hello everyone, I haven been busy for a while and didnt have time to work on my carpc setup. I was finally able to spend some time on it. so here it goes. I built a carpc with the following products:
    inteld525 md motherboard
    ssd hardrive for OS
    regular laptop hard drive for everythingelse
    M3 atx power supply
    custom plastic case with 3 fans
    external usb bluetooth
    nternal wifi module

    I am running windows 7 home premium 64bit along with centrafuse 3.6 with nav. I'm very happy with everything and have dialed everything in. my car is a 2000 mercedes and it has a factory bose amp and speakers. i'm very happy with my factory setup and am not planning on changing it at all. I have replaced my factory headunit with the carpc and made a custom harness to convert my factory speaker wires to RCAs. i have the headphone jack on the computer connected to a preamp/line driver and from there to the speaker wires and to the factory amp. I have this static noise that been there since the begining and it doesnt change with the volume up or done or play or pause, its just always there and very noticeable when music is not playing. i tried many different things such as a ground loop, external sound blaster usb sound card and the static is still there. so i finally ran out of ideas and decided to power up the computer with my battery booster(external booster/power source) and to my suprise not an ounce of noise anywher but as soon as i power it through my oem radio power source the noise comes back again. the external sound card didnt help much either. so now that i know that the cause of the noise is the power source(i'm using my oem headunit ACC, power and ground wires) what options do i have. any suggestions are welcomed. thank you for taking the time in adavanced.

  2. #2
    Neither darque nor pervert DarquePervert's Avatar
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    The solution is pretty obvious:
    Run power to the battery instead of from the headunit harness.
    Ground should run either back to the battery or to the chassis.
    Have you looked in the FAQ yet?
    How about the Wiki?



    Under normal circumstances, a signature would go here.

  3. #3
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    i tried that already, i connected the constant and the ground directlt to the battery and just used the remote/acc from the headunit harness and it made no difference. so what could it be my battery type? do i have to get a second battery just for the PC even though i dont have a sound system? what are some solutions to possibly clean up the power before it goes in the pc?

  4. #4
    MySQL Error soundman98's Avatar
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    what amp are you using?

  5. #5
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    My sound system is all factory from mercedes. It has a bose amp and speakers all factory that came on the car. I checked all the different components and its the carpc that is creating the noise. When i plug a laptop or ipod to the stereo jack there is no noise at all super crisp and clear, also when i powerup the carpc with battery booster(the ones they use to jump start cars) there is no noise what so ever. But the second i power up the car pc with a power source from the car(factory stereo power harness, direct connection to the battery, connection to the jumper terminal inside the engine bay) the static noise is there.

  6. #6
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    Left hand rule

    Look to make sure none of your wires run parallel to any of the car wires
    If they have to be close you have to have a significant part of it running perpendicular
    Don't know if you can do a loop around a magnet

  7. #7
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    thanks for the advise, but as i mentioned earlier my carpc is hookedup to my catory setup. i havent ran any power wires or speaker wires or anything. i just simply replaced my factory nav/stereo system with the carpc and ran a stereo jack to regular wire conversion harness to connect it to the factory system. there is no noise in the system, its the caroc that creates the oise once its connected to the car's battery. so something with the carpc powering up with the car battery is not woeking right because it is grounded perfect as well.

  8. #8
    Maximum Bitrate Mickz's Avatar
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    When you connect a PC to a vehicle electrical system you inject noise from the main SMPS (PSU) and from all digital devices in the PC, IE - Clock signals, data, USB, LCD Screen and its SMPS and the list goes on. This creates earth and feed points that have a high RF and digital noise potential difference. These high frequency AC/pulse noise signals can develop across 3 inches of aluminium chassis which is a far, far superior conductor to digital noise than 10 feet of steel vehicle chassis.

    A few people get lucky and have no noise; most of us have to takes steps to ensure a noise free installation.

    You have to reduce the noise developed across cabling and the vehicle chassis to a minimum, especially between the PC audio in/out and the amplifier input. Cable thickness should be selected for “noise reduction” as well as, and not just for its ability to supply sufficient current to a system. A small system with a lot of noise may need heavy cables to help reduce noise.

    To reduce noise, the PC-PSU should have a direct path to the battery positive terminal with a minimum of "8 gauge" cables for a "small PC system". Both negative and positive cables should be run between the battery and PSU. The PSU-PC should be grounded to the vehicle chassis with the shortest thickest cable you can use and sometimes the exact ground point on the PC chassis is critical.

    As you are using the factory amplifier you could try an 8 gauge cable straight from the main amplifier/ground connection to the PC chassis ground. The shielded cables connecting the PC audio out to the amplifier input should be double shielded with the inner shield a foil and the outer full coverage braid. This will reduce ground induced noise potential difference between the PC and the amplifier to a minimum and help eliminate noise induced into the audio leads from other cables. You may be better off making these cables if you know how as you can save a small fortune, and you end up with better cables than the so called "high quality" crap sold in audio outlets, the cable is only around $3.50 a meter for individually screened/isolated lead pairs.

    In many cases doing these things can avoid the need to use horrid ground loop isolating transformers.

    NOTE: The ground you talk about may be “fine for DC”, it may "NOT be fine” for digital noise / AC interference signals.

    Good luck with the system.
    Last edited by Mickz; 02-06-2012 at 05:02 PM.
    GA-Z77N-WIFI, i5-2400S, 8GB, Intel 520 128GB SSD, M4-ATX Modified, 2 Rev Cams, 2 Web Cams
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    T-Screen HVAC control, custom microcontrollers, code and FE. CarPC Project

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