Anybody have any input on "floating grounds" and GM vehicles?

[SavantStrike]

So, I just got finished doing a long awaited install in my Buick, and I'm getting absolutely horrendous noise out of the amp. I'm 99.99 percent sure it's a bad ground, because it sounds just like it (engine noise in the audio, etc).

I'm going to run the ground to a better location on the chassis, which is all that should be necessary, and I'm also going to ground the head unit to the amplifier (because I ran an extra 16 gauge wire to do just that when I installed it, and while I'm sure some might think 16 isn't enough, 16 gauge is rated for 13A at 110v and 20A at 12V, so it's more than enough for a 10A head unit that will never see any load)

But when talking to a friend who is a weekend warrior type mechanic he told me I need to run a dedicated ground back to the battery because I've got a GM vehicle. He tells me that GM doesn't always tie the grounds to the same spot on the car, and the chassis isn't grounded. And if I don't do this, I'll damage the electronics in the car over time.

Is there any truth to this. Honestly it sounds pretty ridiculous that GM wouldn't ground the chassis of the car (even more so because I'm getting 14.4 volts in the circuit I have right now. What could very well be the case is that there is just enough potential between the ground on the factory head unit and the ground at the amp that I'm getting the behavior I am right now.

Google searching brings up some incredibly old standard where only one wire was run to speakers and the ground for the speakers was tied to the chassis of the car (which is not what I have here any ways).

[truthsayer]

Never hear of gm chassis not being grounded, I have to call bs on that. All my gm vehicles chassis was grounded. I also wouldnt ground HU to amp. Give HU it's own ground.

[SavantStrike]

Never hear of gm chassis not being grounded, I have to call bs on that. All my gm vehicles chassis was grounded. I also wouldnt ground HU to amp. Give HU it's own ground.

Well the entire concept of having no ground on the chassis of a car seemed really stupid to me from the get go. And pretty dangerous to boot.

I can give the HU it's own ground instead of grounding it to the amp, but that's what it has now, admittedly tied into the factory harness with a ground that goes who-knows-where. Grounding it to the amp would mean there is no electrical potential between the amp and the HU, so the RCA outputs should stop acting like giant antennas and picking up electrical system noise.

I can try it both ways.

[ChevyBoy95]

frame is ground in that vehicle....

i would try grounding the RCAs or a better HU ground.

Ground your front battery to the frame, then ground the rear battery to the frame as well.

edit: no real point in grounding the HU to the amp btw.

I would try the RCAs first, usually a big thing.

And what hu do you have?

[SavantStrike]

No rear battery, very small amp.

Head unit is a Kenwood KDX-X597, I don't think I have the blown pico fuse issue that pioneers suffer from. There was a snafu when I first powered up where the factory amp and my aftermarket amp were trying to drive the same speakers (the price I paid for splicing into the factory harness), but I had no issues when I hooked up a completely different source up via RCA's to the amp.

So, I've either got a bad HU, or I've got a bad ground. The ground on the amp in the rear may not be good either, although I'm getting fairly low resistance. I'll check it with an ohm meter tomorrow.

[SavantStrike]

Well, it was a bit of a pain, but I did further testing and narrowed down the problem to either the head unit, or the power to the head unit.

First thing I did was take off all the RCA's on the amp side and jump the remote so it was on. No sound (and no noise), but the amp light showed that it was on. Next I took the only thing I had handy - a DVD player, and put two RCA's from the DVD player to the amp - I ran this with two different CD's, one with a 10 minute silent track, and one with audio on it. The 10 minute silent track did have a bit of hiss (which is to be expected since the outputs from the player were the equivalent of running a head unit at max volume). No unwanted noise though. The audio CD sounded fine, although really loud (of course because there was no volume control on the DVD player).

Then I took the DVD player to the front of the vehicle, and I hooked it up to the RCA's that were previously run to my head unit, and hooked up a pair of them at a time to the amp in the back. Again, I tried the blank audio test CD as well as the music CD. The behavior was the same up front as it was in the back. So this means all of my RCAs are good.

I tried grounding the head unit to the amp in the back (to avoid the possibility of a ground loop) and there was no improvement. I pulled the harness I had installed my head unit with and put in the old harness that tied into the old factory amp, but did not reconnect the factory amp. Still a lot of noise from the head unit.

So, the RCA's are good, they aren't picking up any noise, and the amp in the back is also good. If the ground to the amp is bad, it's not showing up as noise, but it might affect power handling. I need to find a good spot on the chassis to ground to and run an ohm meter between the ground terminal on the amp and the chassis. A bad spot on the chassis (Painted bolt) to the ground on the unit shows 1.1 ohms (which may actually be fine seeing as the bolt I shorted to was painted - this is the one I shorted to to check resistance, not the one the ground is under).

The noise is definitely coming from the RCA outputs on the head unit. I've got an RMA in and and will be receiving a new head unit tomorrow (man I love the vendor I went with). If another head unit is noisy, then the only possibility left is that the factory harness is providing dirty power, although that would be odd as the unit runs fine until I start trying to use the RCA's.

First step is to eliminate the issues with the head unit, next step is to determine if the ground I have is going to be adequate to carry current efficiently.

[n8ball2013]

More than likely your head unit will be the issue.

[SavantStrike]

It was the head unit all along. I also had a bad amp in the back, specifically, the subwoofer channel was bad, the other four were fine. It's not my electrical wiring either - that all seems to check out, but I haven't yet metered it when horsing the equipment, so I suppose there could be some voltage drop (unlikely though, as I'm only running 500-600 watts RMS including the mids and highs). Around 12.5 volts at the amp with the car on accessory and right at 14.4 volts when the car is on and idling.

Everything works as it should, no pops, no hiss (at all), no noises, just clean audio - or at least as clean as the components I selected will allow for. The sub is tuned a bit lower than I had anticipated - probably due to the port being so close to the walls of the enclosure (which was a risk I knew I was running going into this with my models), and as a result it's a bit quieter than expected, but I have not really adjusted my gains at all yet. It would always be nice to have a DD-1, but it would cost about just about half of what my install is worth.

I'll start a build log soon and space out the posts as I get time to fill them in. It's tame by the standards of this forum, but it's clean work and looks pretty nice. A pity I didn't take pictures when I did the doors, that was a lost opportunity.