I tried everything, can't get rid of this ground loop

intense · 07-09-2005, 01:28 PM

Car: 330ci BMW

Battery location: Trunk

PSU: Opus 150 - 10 gauge wire over 5 feet direct to the battery - wire resistance to terminal = 0.1 ohms (basically 0)

AMPLIFIERS: 3 amps, 1 crappy jensen amp for the rear, 2 nice esx amps for front and subs - 8 gauge from each amp to a T block and 4 gauge right to the -'ve battery terminal - wire resistance to terminal = 0.1 ohms (basically 0) - ground length (5 feet)

WIRING: OPUS and AMPS have separate wires

PROBLEM: I get a constant ground loop buzz in the rear speakers through my crappy jensen amp. My quality ESX amps do not have this buzz. On my JENSEN amp I can hear either the CPU fan or Hard disk spinning on boot up and when I move the mouse it makes a additional scratching sound in addition to the constant buzz.

WHAT I HAVE TRIED:
1) unplugging the line input to the card and muting everything in windows.
2) measured all resistance to make sure it was the same across all wires.
3) running my jensen amp off a portable cd player and house power adapter has no buzz.
4) I tried running my computer into my earphones to try and isolate if it was my soundcard that was putting out the buzz or if it was a combination of amps and soundcard. The earphones had no buzz making me think it is a combination of computer with amplifiers, which confirms the ground loop theory.
5) I have tried running the jensen amp, with the ground loop problem, being powered off the car 12 volt but feed a source from a portable disc man running on its own batteries. No ground loop or buzzing.
6) Update: ESX amp testing. I tried the ground loop isolator on the ESX quality amplifiers and there seems to be no change in the audio except for a slight dampening of the fq range. So it would seem that the ESX amplifier ground techniques are far superior to that of the JENSEN's. Outcome was that it sounded better without the filter.

My thought processes is this. At first I thought my soundcard might be passing noise to my amps through the 3.5MM jack ground. But my earphone test should have picked up any ground loops. So, I think it has to do with the soundcard seeing two separate ground paths back to the battery. 1) the soundcard is grounding back to the battery through the opus's ground. 2) then the soundcard now also has a ground back through the RCA's on the amps in the trunk, which then follows a different ground wire back to the battery. So now the soundcard sees 2 different ground paths and by using both paths it somehow picks up noise in the process (I don't see why since both ground wires have the same resistance). This could be causing some weird feedback loop that can only be explained by the crew of the star trek enterprise. The only problem is that my esx amp is not affected by this ground loop. So the only thing I can think of is that the ESX amps already have some form of a ground loop Isolator built in and the JENSEN does not.

To try and fix the above problem I have used a ground loop isolator, which breaks the ground connection between the rca's from the soundcard to my amplifiers. This FORCES the soundcard to be grounded back through the opus and for the amp to use its OWN ground wire. This stopped the ground loop on my JENSEN amp to the best of my ability to hear anything.

I am almost 100 % sure this is the problem now. Let me know if this makes sense or please share any other ideas.

Thanks
CL

intense · 07-09-2005, 04:52 PM

Updated:

z0rz · 07-10-2005, 01:57 AM

So are you still getting the buzz after your update? It sounds like you have tested it thorughly and here are the only suggestions (that won't help you) that I can give:
1. Post this on sounddomain.com
2. Try powering your Jensen amp from a battery charger and your opus from the car battery (try it with the car running and not)
3. Buy a quality amp

That's about all I can think of. Good luck with your problem.

intense · 07-10-2005, 09:58 AM

The buzz is gone with the ground loop isolator. I was always under the impression that they were not a proper fix for ground loops and more of a band-aid. However, I think in my case it is necessary for my JENSEN amp because it uses poor grounding tactics.

If you think of how a regular head unit works, this also needs to be grounded to the battery, so the same issue exists no matter what your installing. There will always be multiple ground paths back to the battery and theoretically there should be nothing wrong with that. It is just important that the resistance path back to the battery is less than about 0.5 ohms no matter what you ground to.

So if every manufacture has to deal with this issue, I now believe it is just poor ground loop isolation and noise suppression in 2 areas. The major area is my JENSEN amp; it just has horrible grounding on the RCA jacks. The minor area; most head unit manufactures probably use different grounding techniques than a pc soundcard would use, since head units are designed for car environments and computers are not.

Oh, I tried your suggestion #2 in my first post and thought about doing #3. However, the ground loop isolator provides a proper RCA ground for my jensen amp, which I think fixes my problem. So I am just going to use that instead of buying a new amp.

Thanks for the comments.
CL

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