Socket7

So I've had my system fully functional for about a week now, and I'm beginning to be slowly driven mad by what i THINK is a ground loop in my head unit.

I've got my amp and LC7 in the trunk. They share a common ground which is less then 0.1 ohm resistance to the negative battery terminal. The LC7 has an option to use an auxiliary input source. When the LC7 is using the aux input, the sound is crystal clear. I couldn't ask for better sound without dropping $250 on an EQ.

When i switch over to the head unit input. I get alternator whine. Badly. It comes out of every single speaker in the car, and becomes louder when I turn my gains up. It does not matter if it's the amp gain or LC7 gain, the result is the same. This leads me to believe that the noise is being generated inside my head unit, and passed through the speaker outputs where it's then amplified (along with the signal) by the LC7 and then my amplifier.

My question now is, how the hell do I stop this? The LC7 has different grounding modes, Isolated, Grounded, and 200 ohms, but changing these jumpers does not seem to have any effect on the noise. I also tried running a dedicated ground wire from behind the head unit and grounded it to the trunk along with my amp and LC7, but this did not work either (maybe the wire gauge was too small?).

I'm at a loss at this point. Have any of you had a similar experience when upgrading the stereo and keeping the OEM Bose head unit? More importantly, how did you solve it!

canaryrx8

iTrader: (3)

bad rca's maybe? Could try grounding at the battery as well maybe? one other thing I've seen is rca's being too close to other rca's/signal wire

Socket7

I doubt it, but thats easily testable, and I haven't done so yet. If it was creeping in on the RCA cables, then theoretically, adjusting the gains on the LC7 should not effect it. Only adjusting the gains on the amp would make it worse. I'll try at lunch.

I have tried running a dedicated cable from the head unit to the LC7 in case it was coming in through the wiring harness, but no dice. It's gotta be getting into the signal from inside the head unit is my gut feeling.

Socket7

Ok, I went out and monkeyed around in the trunk. Took the front and rear RCA cables, pulled them out of their hidey holes and connected them directly to the amp. Same noises, and it's also coming from the front and back speakers. So it's not the RCA cables. I was able to change some settings on the amp to get rid of some other noise i was having, which is cool, but it's done absolutely nothing to take care of the alternator noise.

canaryrx8

iTrader: (3)

hmmm, perhaps a ground somewhere then? Most of the cases I've run across in past installs with noise were crappy signal cable, power wire to close to signal cable, and bad/weak ground. If it's none of these things or you've already tested for them then it's probably time to start fiddling with the head unit (?) Maybe try taking it out of the dash and seeing if you can kill the noise unplugging stuff from the back of it etc. with the car running? Just throwing stuff out there, maybe it'll trigger something you haven't though of

Socket7

I'm really tempted to run a 10 gauge power and ground wire from the back of the head unit to the battery, but that means taking the head unit out.... AGAIN.

rollerbldes

You can try a ground loop isolator, I'm not sure how exactly you would wire it.. But I can think of ways you could retrofit the radio shack one.

You could also pick up a few ferrite beads and try to work those into your wiring. There is no guarantee that this will work though.

Socket7

Ok. So here's what I think is going on. The stock head unit and Bose amp both ground to the dash, behind the head unit. The amp and LoC are both grounded in the trunk of the car. The difference in ground potential is causing my alternator whine. (different ground reference voltages == noise)

What I'd like to do is unbolt the ground wire from the dash and connect it to some 10 gauge wire that grounds in the trunk. The problem with unbolting it is that there is no way I'll ever be able to reach the ground to work on it back there.

This leave me with the option of cutting the ground from the J-01 connector and soldering it directly to the 10 gauge wire. Also a pain in the *** to do, but far more possible then the other options. I'm hesitant to do this as I'm worried that something might break (I can't think of a reason for it to, it's just a ground wire, but I'm paranoid about my baby)

Do I try and get behind the dash with a spanner or do I pull the head unit again and ground the HU direct to the trunk by cutting up the wiring harness even more?

firebirdude

iTrader: (3)

Have you tried grounding everything to a completely different location in the trunk? I know you said you metered it..... but hey.... you've tried everything else and I've seen crazy things happen.

Go with more gain on the LC7 and less on the amp.

Tigerfootball

I feel your pain. Using the Rockford Fosgate 3Sixty.1, I have to keep it set so that the supplied volume/bass **** be the main volume control because with is set to allowing the radio to be the main volume ****, the whine was too bad. With it set to allowing the 3Sixty to control the volume, the whine is VERY low, but still there. I have tried everything. Let us know if/how you solve your problem and I am sure that will probably solve mine as well.

Socket7

The last time I had my head unit pulled I actually soldered a wire onto the ground line coming out of the HU connector. I just tried grounding the LC-7 through it and I'm still getting the noise. I also went through and tried the different grounding settings in the LC-7 Grounded, Isolated, and 200Ohms. All sounded exactly the same.

So to recap.

LC7 and amp grounded in the trunk. = alternator whine. Changing LC-7 jumpers has no effect.

Amp grounded in trunk with LC-7 grounded to head unit = Same whine. Changing LC-7 Jumpers has no effect.

Running an alternate set of signal wires away from any interference from head unit to LC-7 = Same whine.

Using the aux input instead of the head unit for any of the above combinations == no whine at all.

I'd run the whole goddamn amp through the test wire I put in, but I don't think that 14 gauge wire is going to be enough to ground an amp of any kind.

Gain adjustment doesn't really help much. I started with the gains on the LC7 being almost maxed out (according to the install instructions you're supposed to turn them up until the maximized light flickers, and it never did). All it really did was stress the inputs on my amp and make it run hot. They're set to a little over 50% right now. I'm not adverse to playing with them, but having fiddled with this for over a month now, I can tell you that any gain adjustment is not going to be a fix for this problem, and using it as a band-aid would seriously effect my ability to use my system to its full potential.

jstkilntim

Where are your LC7 input signals coming from. Bose HU or amp?

Socket7

Connected through the head unit itself. Bose amp applies a gross EQ curve and I'll have none of it, thanks. Bose amp is actually completely disconnected at this point.