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  • PC Causing Noise, Suggestions?

    First, I have narrowed the problem to the PC: plug in an mp3 player and the noise dissipates.

    I am assuming my issue is with grounding (the psu, motherboard, graphics card, or pc case). I am pretty good at troubleshooting but my technical understanding leans towards novice when it comes to audio (car audio). Therefore, I've come here to download your insights.

    My thoughts on isolating/fixing the issue:
    • I tried grounding the pc case to the psu ground. No difference.
    • I have not yet tried running a ground cable to the battery directly--that will eliminate my psu to body ground point as the source. If ground is issue, yay, find new ground though I anticipate that is not the problem.
    • I would prefer not putting some device inline on the rca/audio cables if there is another solution.
    • I believe the noise is caused by the system fan. If the noise persists after grounding to the battery it will confirm that, right?
    • If it is system fan, would an aftermarket fan do the trick or go with some fanless heatsink and run a (few) san ace h1011 at low rpms wired to the ignition??

    Any suggestions? Is this caused by some ground loop? (I don't understand ground loops)




    Let me know if I left something out or need to clarify... I'm a few beers in.
    Thanks!!

  • #2
    did you try grounding the shield(common) of audio cable? this way you will take both the amplifier's input common and sound card's output common to the same potential level.
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    • #3
      It is probably a grounding issue, that is true. Try grounding your power supply to not the battery at the feet/case of the alternator, or directly to the frame (whichever is closer/more convenient). Make sure to clean the surfaces very well with a wire brush, and keep your ground cable as short as possible. Also make sure you're using high quality RCA cables with solid connections on the PC sound card side as well as the amplifier side. It is not necessarily caused by the fan; there are MANY causes of noise in an automotive setting, as well as in the computer itself. High frequency electronics are, well, noisy, so getting rid of these causes of noise is an iterative process.

      You may also look in to a better sound card (if you're using a cheap one) to eliminate some of these aforementioned noise sources. A high quality sound card can go a long way because often, on-board sound cards are quite poor.

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      • #4
        So I was about to order an aftermarket heatsink and got the idea to unplug the system fan to see if noise persisted--it did.
        So I turned off the truck (with pc on and fan plugged in) and sure enough the noise went away. Looks like it is a grounding issue. I guess it is alternator noise, though increasing rpms doesn't make the noise noticeably worse.

        Is it safe to assume the psu ground is the issue since the noise does not persist when connecting an mp3 player? (and not some other ground?) It would take some effort to move this ground unless I ran a self tapper through the firewall.

        If the psu ground isn't the problem would I need to ground the audio card directly to the body? Or the pc case to body?
        Last edited by mrwesth; 01-21-2013, 10:30 PM.

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        • #5
          I ground everything to the frame, using high quality lugs and brass bolts. Like I said, in an automotive environment, there are plenty of sources of noise, so eliminating any grounding issues you can (right off the bat) might end up saving you hours of headscratching and frustration. It's never safe to assume anything, so start off with an excellent ground to your PSU, and go from there.

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          • #6
            ^ yep. you can also temporarily try grounding the outside ring of the rca's to the same ground wire the psu uses-- in some cases, this can fix noise issues by draining unwanted noise-- it doesn't always work, but it usually only takes a few minutes to try, so it's always worth a shot..

            though from what i can tell, you're using the m4 psu, which is a notoriously noisy psu(see mickz 's work on the lengths required to correct that).. another option that was touched on is to move your ground point. a good first step is to temporarily try grounding the pc to the negative battery terminal-- if that works, then it's indicative that your carpc's chassis ground isn't very good. at that point, you could start trying some other solid points through the car(it's kind of a shot in the dark-- with today's cars using spotwelded sheet metal, some welds aren't as good as they should be, so they have higher resistance then other welds)
            My OLD 2001 Mitsubishi Eclipse GT:
            "The Project That Never Ended, until it did"


            next project? subaru brz
            carpc undecided

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            • #7
              Good information.
              I never considered that the PSU itself could be causing the noise. I will run a temporary ground to the battery negative when I get a chance and go from there.

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              • #8
                just remember that solutions to ground loop problems like this are nearly always going to be a complete shot in the dark--the only consistent thing is the problem... we could recommend 99 different ways of connecting everything to reduce/eliminate it, only for you to make your own solution on the 100th try that is the only one that completely works.

                just try to roll with whatever punches the install dishes out, and try not to loose to much hair, or sleep over it
                My OLD 2001 Mitsubishi Eclipse GT:
                "The Project That Never Ended, until it did"


                next project? subaru brz
                carpc undecided

                Comment


                • #9
                  Originally posted by soundman98 View Post
                  just remember that solutions to ground loop problems like this are nearly always going to be a complete shot in the dark--the only consistent thing is the problem... we could recommend 99 different ways of connecting everything to reduce/eliminate it, only for you to make your own solution on the 100th try that is the only one that completely works.

                  just try to roll with whatever punches the install dishes out, and try not to loose to much hair, or sleep over it
                  Well put!

                  Taking my own thread slightly off topic:
                  Fortunately I have had a number of tech jobs in different fields where a large part of the job was troubleshooting... both new installs and old shoddy work. Needless to say I jumped ship and am in grad school now as the money wasn't worth the hassle. However, I did get a lot of satisfaction from finding the solutions to problems others couldn't.
                  That goes right in line with why I enjoy tinkering with projects like this and the challenge to overcome each hurdle. I think that 90% of my interest in going the car pc route was for the fun of the install (and subsequent tinkering to get it just to my liking).
                  I'm sure the same holds true for many others that take on these projects.

                  Back on topic:
                  I just need a free weekend (ie not pending midterms or research papers to write) and a case of beer and I have no doubt I can take care of the noise issue.
                  However, in the meantime is there a good read on learning more about ground loops? I have at best a rudimentary understanding. Are there any good diagrams of ground loops in a car application? Google searches show some home theater setups and it seems the ground loops there are always caused by two connected devices. Would that be the amp and the carpc--and the loop is through the rca connection? Or could a loop be caused by multiple grounding points from engine block - body - frame?
                  I would love to understand what causes the problem rather then simply troubleshooting until it goes away. 'Cause learning is fun, yo.

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                  • #10
                    I think running 0/1 cable front to back is a waste really. You really only need to run a short piece from negative battery terminal to frame as the frame of vehicle is one big metal cable. Also try an keep wires in direction of flow (it makes a big difference in DC wiring) just my 2 cents SNO

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                    • #11
                      Make sure to upgrade the ground straps from the engine to the body however.

                      And if you have any other heavy battery cables going to the body of the car make sure those are up sized as well. As I mentioned elsewhere most cars normally have a ground strap that almost looks like bolted wire mesh that goes between the engine block and the body of the car.

                      My old cop car had two ground straps from the engine to the frame and had 4 separate ground straps from the frame to the body of the car. 2 of them were from the exhaust pipe to the body of the car. These were all factory installed.

                      Do not rely on the body mounts to pass the ground signal from the engine to the body of the car especially since in most cases the engine mounts are rubber or plastic bushings.

                      You want to use the same type of cable that the factory uses. So if you are replacing the battery cables themselves they are generally quite small from the factory. I think it is common for instance for GM to use 6 gauge wire. In any vehicle I am not running power cables directly to the battery I would always up size the cables to the car its self. So you would want to go to a 4 or 2 gauge wire in those cases depending on the size of your install. The ground strap can be a little harder to find but it is designed to handle high temps, oil and gas spillage. It is simply a copper mesh with connectors on both ends. You can add more of them to add more capacity or get bigger ones.

                      If you know of a good grounding point on the frame you could also run a standard cable from the battery directly to the body of the car away from the engine.

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                      • #12
                        Originally posted by mrwesth View Post
                        Well put!

                        Taking my own thread slightly off topic:
                        Fortunately I have had a number of tech jobs in different fields where a large part of the job was troubleshooting... both new installs and old shoddy work. Needless to say I jumped ship and am in grad school now as the money wasn't worth the hassle. However, I did get a lot of satisfaction from finding the solutions to problems others couldn't.
                        That goes right in line with why I enjoy tinkering with projects like this and the challenge to overcome each hurdle. I think that 90% of my interest in going the car pc route was for the fun of the install (and subsequent tinkering to get it just to my liking).
                        I'm sure the same holds true for many others that take on these projects.
                        i was the same way.. i really enjoyed trouble shooting low voltage stuff at my last job-- i was the best tech they had(many places requested me to service any of their issues instead of just letting the company send out a random tech)... but the money just wasn't there..

                        Originally posted by mrwesth View Post
                        Back on topic:
                        I just need a free weekend (ie not pending midterms or research papers to write) and a case of beer and I have no doubt I can take care of the noise issue.
                        However, in the meantime is there a good read on learning more about ground loops? I have at best a rudimentary understanding. Are there any good diagrams of ground loops in a car application? Google searches show some home theater setups and it seems the ground loops there are always caused by two connected devices. Would that be the amp and the carpc--and the loop is through the rca connection? Or could a loop be caused by multiple grounding points from engine block - body - frame?
                        I would love to understand what causes the problem rather then simply troubleshooting until it goes away. 'Cause learning is fun, yo.
                        simply put, a ground loop is a difference in voltage potential to ground.

                        think of the carpc and the amp as 2 glasses of water, and think of the rca cable as a tube running between the glasses. if you take water out of the 'carpc' glass, water is going to rush in from the 'amp' glass to replace it until the water level in each glass is exactly even. and if you were to remove some water from the 'amp' glass, water will again rush in from the 'carpc' glass until everything is even.

                        that is essentially what is happening with a ground loop, except that one glass is constantly trying to be emptied, and the tube is constantly trying to make up for it.

                        usually a ground loop is caused by different resistances-- either because one device is using a longer wire to reach a shared ground point, or the ground point connection of a device has a higher resistance then another interconnected devices separate ground point..

                        the idea that needs to be accomplished is to get both devices evenly matched, so voltage isn't flowing between them-- that voltage is what is causing the whining.

                        and that is about as far as you should need to know for the methodology to fixing it ground loops are insane little gremlins that pop up whenever they feel like it.. you could just throw a sound system in 'just for a weekend' and won't have a single problem with it no matter how hacked, or i've seen it plenty of times where someone will spend hundreds more then they need to, to make every effort to avoid a ground loop situation, only to end up getting a ground loop..
                        My OLD 2001 Mitsubishi Eclipse GT:
                        "The Project That Never Ended, until it did"


                        next project? subaru brz
                        carpc undecided

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                        • #13
                          So I had a free hour today (had to deal with laptop hdd crash last weekend :shakefist: ) and here is what I tried and found:
                          • Ran 8awg from psu to battery negative -- caused little to no change, perhaps slight noise increase.
                          • Ran 16 from rca ground to psu ground post -- caused the noise to increase.
                          • disconnected psu ground and connected phone mp3 player to rca -- noise eliminated.

                          Does this mean the PSU is the source of the noise? I do have a 400w inverter and 250w desktop psu I could try.

                          I believe there are 2 distinct noises:
                          (1) a low volume but high pitched whine when I rev up , I assume this is the alternator and
                          (2) a static like ringing that cycles on and off lasting 3-5 seconds and going off for a second, I am guessing this is caused by the PSU?
                          The whine is not so noticeable, the ringing is very irritating and only drowned out completely at 50-75% plus volume or driving 60 on the interstate.

                          My other thoughts for the source of the problem:
                          • Something with my two battery setup. The factory amp is connected to battery 1 while the psu/subs are connected to battery 2. But I would think that wouldn't matter with 0/2 connecting the two positive battery posts directly, right?
                          • I guess my last thought goes back to a ground loop. I like the 2 glass analogy and that begs the question here about something I may have neglected to mention: the wiring harness.
                            I know this wiring harness is grounded to a small gauge wire that was for the stock radio. It is perhaps smaller then my rca's ground as I am running 16awg per channel and have a total of 4 channels running to the wiring harness. That means a total of 16awg x 4 grounds running from the harness to the pc.
                            Maybe I should try splicing the wiring harness ground to an 8-10awg and ground each of the rca's at the wiring harness side to the same ground point?

                          Thoughts?
                          Last edited by mrwesth; 02-02-2013, 04:32 PM.

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                          • #14
                            Solved!
                            Finally got around to re-grounding the wiring harness. Ran it to the psu and both sources of noise go away. Appears it was a ground loop after all.

                            Thanks for help and suggestions!

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                            • #15
                              great to hear you got it all worked out!
                              My OLD 2001 Mitsubishi Eclipse GT:
                              "The Project That Never Ended, until it did"


                              next project? subaru brz
                              carpc undecided

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