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Thread: Finding good ground to prevent Ground Loop

  1. #11
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    Quote Originally Posted by Matthew230
    I tried running everything to the HU ground, neither that or a Isolator solved my problem.
    I'm surprised the Isolator didn't work.

    Ground Loop is a total B1TCH to get rid off. So glad it hasn't been on a problem on my current car. (Although we'll see what happens when I bung this laptop in!)

  2. #12
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    Quote Originally Posted by lookinco
    Since ground loop is caused by difference of resistence, then if I measure different ground points and get similar resistence measurments, therotically the ground points should be good to not cause any ground loop..right?
    No. That's about the most unscientific thing I've ever heard!!

    Connect the grounds of all your audio equipment to the same place on your chassis. (And if possible make a new ground point).

    In my car I bolted my ground cable to part of the boot. A short 4 gauge cable leads to a distribution block and everything audio related in the vehicle takes it's ground from that distro block. My headunit is powered by cable that runs to the back off the car from the dashboard.

  3. #13
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    So would you recommend me to run a big fat cable from the dash to the trunk and ground the headunit and everything together as well as computer and amp? But I thought the ground cable should be as short as possible?

    I thought in order for a ground to be good there should be as little resistence between the grount point and the negative post of the battery. Let's say i have 2 ground points A and B. When I measure the resistence between battery and point A i get 0.3 ohm, when I measure between point B and battery i get 0.4ohm. When I measure between point A and B, I get around 0.3ohm as well. So would I have ground loop trouble if I hook up headunit to point A and computer to point B.

  4. #14
    Low Bitrate Prem's Avatar
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    Ground loops.... What a pain in the ***....

    I also have a ground loop problem. Fortunately for me I have used a ground loop isolator which has fixed most of my problems. I still have background noise from within the pc though.

    Quote Originally Posted by Engram
    Ground Loop Isolators (excellent bits of kit) are actually 1 to 1 transformers. For anyone that's studied electronics you'll know that only AC can pass over a transformer, not DC. That's how the isolator filters the noise back out.
    But just to point out that any coil has a frequency response range and you WILL loose top (treble) and bottom (bass) frequency response (to some degree...). Some people who run top end audio equipment will tell you that an isolator is the worst thing you can do. But I believe that it is a case of horses for courses. I haven't got the 'be all and end all' of audio systems so an isolator suits me fine.

    In my quest to find my ground loop problem I went to the extent of running my carpc on one battery and my amp on another battery (totally isolated). Everything was fine. I then connected the grounds of the two batteries together which then caused the wretched noise to come back.

    I am therefore left with one conclusion:- Somewhere there is a ground loop in my pc......

    NOW WHAT DO I DO???? Back to the isolator.

    As for resistance testing ground points. What is more interesting is measuring the voltages (usually mV) between ground points.

    Ground loops.... What a pain in the ***....

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  5. #15
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    You never said what you get when you hold the probes together?

  6. #16
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    Mr Perfectionist, you did not quite understand my post correctly. Maybe I again wasn't clear enough...

    The statement I made "Granted, a spot weld can handle hugh amounts of current, but because it is a small juncture, it has a higher resistance" is correct in comparison to a solid piece of metal, or a a full length weld, which is what I was trying to state. Sure, it is a minute difference, but it is there. That also makes my other statement "the point being made is that due to spot welds, there is less electrical connection between body panels and chassis, therefore more resistance, therefore, higher chance for ground loop" correct, even though once again it is minute (extremely minute even).

    I completely agree with you that likely the body is not properly grounded to the battery, however, my conclusion is still correct: grounding to the "frame", whether it be pressed or "monoque" is likely a better option than using the body panels.

    Say I'm wrong about the welds causing ground loop, fine. But don't mess with my point: using the frame is most likely better than the body. The site I was reading is dedicated to high end audio. They measured output preformance and made comparisons of output versus ground points in various vehicles. There was always a gain in sound pressure levels when using the frame for grounding, as opposed to any other location. I'll post it if I can find it again.

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  7. #17
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    When I put the two probes together it reads 0.2 ohm
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  8. #18
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    Quote Originally Posted by lookinco
    When I put the two probes together it reads 0.2 ohm
    So basically these resistances are negligible. Don't worry about them.

    I've always wondered why they say "use a short ground cable". It must be to do with power loss. After all the vehicle chassis is acting as a conductor so what's wrong with adding a bit of cable to it as well. (Other than an overall increase in resistance and therefore less power for amps).

    Choose a ground point in your boot/trunk and attach everything that needs grounding to this point. That includes running a ground cable from your headunit back to this point.

  9. #19
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    I think Ohm measurements suck and are inaccurate, I had a noise on my system (alt. whine). So I got my ohm meter, checked my grounds and all showed 0 oHms (well 0.2, whatever)
    Added an additional ground wire to my Opus and ran it to the "main" ground point, noise still there. I then tried several other locations, all the points that read 0 oHms, noise still there. I then left my pc and music on (with the whine) and just touched the ground wire all over the place until I found a spot that caused the whine to clear.
    Point is: even though all these places (except the last place) read 0 ohms, apparently those "0 oHm" grounds weren't any good.
    A voltage drop test is much more accurate, (my 2 pence)
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  10. #20
    Variable Bitrate HummDinger's Avatar
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    When grounding your computer use equally as thick grounding cable as you do power. Also power your computer or inverter directly from the battery. Do not hook it up to any accessory plug or wire in your car. Next get your self a silent or quiet power supply designed for in car use. USE Propper high quailty wiring, I can not stress this enough.
    I had the line noise problem for 1 year and was just starting to get use to it, then I decided to re-wire when I changed out computers. I used an amplifier wiring kit (high quality oxygen free cables, 10gauge) hooked my inverter up directly to the batt and walla, no line noise.
    Yes, I use an inverter. Just a cheap one I picked up at the hardware store for about $50.00. I still use the 200 watt 12V PSU but with a power brick since hooking it up directly to the batt is not really recommended. I also use the $69.00 power controller found on ebay to control the shut down and startup procedure for the computer and inverter. All works great and I could'nt be happier.

    Line noise has allways been a major topic and the answer is allways a good ground, correct wiring and enough power to your system IE thick enough cables.
    You can still have something if you have nothing

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