check my diagram minimizing ground loop

Sorry for the lengthy explanation - diagram is at the bottom of the page.

I'm rewiring my setup in a few weeks. I had some alternator noise coming through (very slight) but enough to hear if you listen closely. The battery is a DieHard 700cca/120m reserve, and is located in the trunk because the turbo requires the space where the battery once was located. I am considering a HO alternator to mitigate some of the charging issues associated with the battery's remote location, and already have some 1/0 ga.

Anyway, the HU is a Pio Avic D3x and drives only the tweeters and rear door speakers, directly. The rear deck, sub, and front door speakers are powered by two amplifiers.

The thicker red and black wire is 1/0ga. The thinner red and black are 4ga. Brown wire will be shielded, twisted-pair RCA. Green and purple wire are 14ga and come from the amps (red rectangles). Blue wire is line-level directly from the HU and will also use 14ga (except for the tweeters, which will retain stock wiring).

To take you around, here's what I'm considering:
At the battery, 1/0ga to a volt/ammeter, to a 300A fuse/circuit breaker, to a distribution block, which will power the two amps and capacitor with 4ga each, and also go back out to the original junction block located in the engine bay and to the alternator with 1/0ga.

The ground side of the battery will be 1/0ga also and go to a terminal mounted in the trunk (chassis ground) and then directly to the transmission grounding point (original battery ground). This is the part that i'm not sure about. Should I just leave the ground in the trunk and not worry about routing it back to the original trans grounding point? I'm not certain about the conductivity of the trunk interior for use as a ground.

My main concern is preventing ground loop noise through my speakers. The brown lines are RCA pre-amp outputs from the HU that will pass underneath the carpet through the center of the car as shown to prevent noise from the 12V power lines that run along the outside rails. The amps will be grounded to individual chassis grounds (trunk - again, maybe these should ground directly to the battery or ground power line?). Any suggestions here for minimizing ground loop? Could the stock antenna wire be causing some ground loop noise, even when not using AM/FM? Do I need the HU grounded directly to the battery?

I've heard of some Pio HUs that blow pico-fuses that translate the HU chassis ground to the RCA output grounds and people have developed an easy solution by wrapping wire around the outside of the RCA pre-outs and bolting it to the HU chassis.

I can continue to revise the diagram as you offer suggestions, so please spare no mercy:

'03 Nissan Altima

no suggestions?

I would fuse those long-ass cable runs from the alt to the battery, but assuming your resistance readings are all what they should be it should work fine.

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I have never seen so much concern over a ground loop that has not occured yet.  Or has it?  If so is the noise so loud that they can hear it in the car on side of you at a red light?

are you using the factory ground for that D3? this could be the cause of your minor ground noise you have already. if the fuse inside the D3 was blown trust me, you would know it, but a not so good ground on the radio could cause some minor ground noise

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Have you tried turning the gains down until the noise goes away?

DYohn] wrote:

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I would fuse those long-ass cable runs from the alt to the battery, but assuming your resistance readings are all what they should be it should work fine.

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There's a fuse/circuit breaker shown right after the volt/ammeter near the battery terminal.

i am an idiot wrote:

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I have never seen so much concern over a ground loop that has not occured yet. Or has it? If so is the noise so loud that they can hear it in the car on side of you at a red light?

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There was some noise with my previous setup, as I said in the first post. It was minimal, though.

soundnsecurity wrote:

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are you using the factory ground for that D3? this could be the cause of your minor ground noise you have already. if the fuse inside the D3 was blown trust me, you would know it, but a not so good ground on the radio could cause some minor ground noise

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I am using the harness ground, IIRC - I'll have to double check. I should upgrade to a better ground for the D3, perhaps an engine/trans ground point? I will also try that RCA terminal-to-HU Chassis ground mod that seems to work well.

i am an idiot wrote:

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Have you tried turning the gains down until the noise goes away?

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I haven't tried that yet, as gain needs to be at least half way up in order to produce a satisfactory amount of loudness.

digitalbow wrote:

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DYohn] wrote:

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I would fuse those long-ass cable runs from the alt to the battery, but assuming your resistance readings are all what they should be it should work fine.

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There's a fuse/circuit breaker shown right after the volt/ammeter near the battery terminal. .

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OK, but what about between the alternator and the battery?  That looks like a long run of unprotected wire that is connected directly to your source: the alternator.  It needs to be fused at the alt, or at least at your connection block in the front of the car.

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digitalbow wrote:

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[

i am an idiot wrote:

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Have you tried turning the gains down until the noise goes away?

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I haven't tried that yet, as gain needs to be at least half way up in order to produce a satisfactory amount of loudness.

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You need to set your gains properly!!!  Check the Car Audio hot topics forum.

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DYohn] wrote:

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p>OK, but what about between the alternator and the battery?  That looks like a long run of unprotected wire that is connected directly to your source: the alternator.  It needs to be fused at the alt, or at least at your connection block in the front of the car.

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Oh, I see what you're saying - yeah that connection block still has the OEM fuse block. It's fused there - i'm replacing the wire from the alternator to the fuse block w 1/0ga. The run from there to the trunk is fused again closer to the battery.

DYohn] wrote:

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p>You need to set your gains properly!!! Check the Car Audio hot topics forum.

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I suppose the gain for the sub could be tweaked a bit, but as far as the full-range F+R, they're done pretty well. Gain is about half on the amps, with the HU's EQ adding 1 level to bass and high-treble, each.