Thread: Proper grounding question

Is the video coming from the PC or DVD player when you notice the noise? My understaning (and config) is that your audio source and amplifier should have a common ground, and that the ground wire should be as short as possible (usually the shortest run is to the chassis and not back to the battery).

I'm not sure about the gauge of the ground wire, but it's usually the same as the positive lead. Regardless, I doubt the gauge of the ground wire would cause noise.

The noise is present on both the dvd player and PC. I think I'll try just one ground point at the battery and remove the chassis ground points and see if there is any change. I could upsize the ground wire but I think 10ga would be sufficient based on the fact it is larger than any of the power wires I have feeding the equipment.

I redid all my ground point to the chassis, removed the 10ga, and ground loop isolator to try and do this the correct way. Whine still there...If I bypass the video switcher and amps the system is dead quiet playing through the PC. I measured the ohms between the battery and the ground point, at the PC it is 0.02, at the video switcher and amps it bounced between 0.02-0.03. When pluged in with the amp or the videoswitcher the noise is there. Its about the same individually or with both hooked up. So I bought a power line filter...no difference. The audio quality also sounds bad. I put the ground loop isolator back on and it's much better now and the sound quality is back the whine is noticably less than when I started. I guess the ground at the switcher needs to be exactly the same as the PC ground? I give up for now trying to do it the "right way".

When trying to figure out the sound quality thing I figured out that the mini jack to RCA plug adaptor that came with my sound card are wired backwards...or I am. I ran red to red all the way through and tapped the hu wiring for the right channel, and white to white for the left. When going through the sound card test I found that the red on the adaptor was actually the left channel. Is this standard? I was thinking it was standard for red to be right ...they both have an "R" in them

I believe alternator whine is usually due to a ground loop. What I found strange was that it only occured when you played a video. Loop isolators will help reduce audio system noise caused by a ground loop, but probably won't help alternator whine and only serve as a work-around for the real problem.

During my project I'm learning how important a common ground location is for all equipment that connects to each other with signal cables (audio, video, etc..). I put all my equipment as close to each other as possible and then created a central grounding point. Since you probably have a good set of signal cables coming from the PC (audio and video at least), I would definitely make sure the PC and amp have the same ground. Good quality power cable should reduce the resistance.

As for RCA, left is white and right is red last I checked.

Originally Posted by dune

What I found strange was that it only occured when you played a video.

The noise is there for other sources as well it just is more noticable when playing videos. With the PC going directly to the HU I can turn the volume to max (with nothing playing of course) and there is no noise whatsoever. When the vehicle is running there is no whine either. Plug in either the amp or switcher and turn it clear up I hear all sorts of background noise and the alternator whine comes in when the vehicle is running. You have to have the volume up above about 60% for this to start to be noticable. I'm positive its a ground loop issue between the PC and the other components. I wonder if I were to run a #4 gauge from all the ground and tied to the PC if that would work. If it doesn't get any worse than it is now I'm not messing around with it anymore...the wife and kid are about to leave because of the amount of time I've put into my project the last week or so.

Originally Posted by dune

As for RCA, left is white and right is red last I checked.

Thanks I was thinking I'd lost it. If I find another adaptor around here I'll try switching it and see if the adaptor I have is really switched or if I just f'd up and got things switched when I spliced into the HU. Either way its an easy fix just flip the connections at the PC and peel the colored tape off the RCAs back there

Fixed the f'n alternator whine . I was playing with the audio controls and muted the line in while a video was playing and the whine went away. So after some messing around I figured out it was the XM direct causing the problem. I put on some high quality RCA's and it was still there. I attached the drain line on the RCAs and I got this high pitched skreech for a second when the computer came back up? So I undid the drain line, and grounded the xm direct case, no more whine. So I hooked up the drain line again and sqreech returned. I don't know what the deal is with that but it's an easy fix, just don't hook it up. I took the ground loop isolator out and the sound quality improved too.