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.
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.
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 at 09:30 PM.
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.
^ 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)
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.
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
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.
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