Chassis Ground for Amp Hookup?

[mendo]

Originally Posted by mellowtoad

Just want to verify:

'Hot' = 15 - 20 Feet

'Ground' = 11 inches

So, I should go ahead and cut it? I paid a lot for the cord, haha. I'll give that a try and report back.

Cut it.

and to answer you Cube, stop pasting stuff from the internet without all the info.

yes, long wire can be a cause of voltage drop. You can use this formula to find out how much you will realize:

VD=(2×K×I×D)÷CM

VD=Voltage Drop

K=represents the DC resistance for a 1,000-circular mils conductor that is 1,000 feet long, at an operating temperature of 75°C. K is 12.9 ohms for copper

I = The load in amperes at 100% (not at 125% for motors or continuous loads)

D = The distance between the load and the power supply.

CM = The circular mils of the circuit conductor as listed in NEC Chapter 9, Table 8

Using this formula, you will find that in order to see an acceptable voltage drop of less than 3 % if your amplifier draws 50Amp and the wire is 10 feet, you must use #4 gauge CU wire. Yes, you want to make it as short as you can.

as for using the car, You can if you want. But think about shoving that same 50amp load that requires a #4 Cu wire, (the copper part alone inside the insluation is a little larger than a pencil) back through the metal of the body. the current has to go somewhere, CU is much better conductor than the metal of the body. the current is trying to find it's way back to the battery and leaking all over all the rest of the circuits in the car.

the method you copied is ok for very small, low current devices. The cheap ones will still be prone to noise.

it's up to you,

[cubefx]

mendo,

I could post some photos of my 500+ RMS amps in my other cars.
I always did my own installs and never have any noise leak issues. I was always told to keep ground wire under 12". The reason I posting the links is that after yor post I searched but could not find a single reputable reference that would state that it is necessary to run the ground wire back to the battery. Best I could find is that technically you can do it, but there is no point because good ground point is will be as good.

Sorry if my posts above sounded rude, that was not my intention.


Peace.


CUBE


P.S. Posting from the phone sucks. Sorry for typos.

[mellowtoad]

Aggg! I cut the wire and still the same issue. Driving me nuts. I also now have a six inch ground wire. My RCA cables are still long, should those be trimmed as well? If I do, can they be spliced liked normal wires?

[cubefx]

Originally Posted by mellowtoad

Aggg! I cut the wire and still the same issue. Driving me nuts. I also now have a six inch ground wire. My RCA cables are still long, should those be trimmed as well? If I do, can they be spliced liked normal wires?

No, you can not splice RCA wires. Try to route you RCA cable some other way just to see if it will fix the problem. It possible that you have some kind a power wire near it. Also, did you use "Car audio" grade cable? Just want to make sure that you did not used cable for home equipment.

Also, if the cable is too long it will more likely pickup interference. I would also try shorter wire if everything else fails. Again, make sure that you use quality shielded RCA cable.

[mendo]

Originally Posted by cubefx

mendo,

I could post some photos of my 500+ RMS amps in my other cars.
I always did my own installs and never have any noise leak issues. I was always told to keep ground wire under 12". The reason I posting the links is that after yor post I searched but could not find a single reputable reference that would state that it is necessary to run the ground wire back to the battery. Best I could find is that technically you can do it, but there is no point because good ground point is will be as good.

Sorry if my posts above sounded rude, that was not my intention.


Peace.


CUBE


P.S. Posting from the phone sucks. Sorry for typos.

No Worries Cube.

[HGB]

Mellotoad,
if possible and maybe you tried this already, hold the RCA cables and gently move them around and away from other nearby cables while the engine is on. Is there a variance in the whine?
Is the whine on FM, AM and CD the same? Is the whine the same loudness at higher and lower volume settings? Is the amp itself grounded (bolted) to the chassis? Im just curious.
Besides scientific issues, somewhat black magic help sometimes. I don't mean to step on contributions from others, yet when one is stumped all avenues are open.

[mellowtoad]

@HGB - If I move the RCA cables, I get no change at all. I get the engine hum with the cd player/mp3 player/radio on. I also get the same amount when the head unit off period. Changing the volume on the head unit doesn't make a difference, although changing the gain on the amp does.

I also have tried hooking it to every ground I could find. Tomorrow I'll try moving the amp from under the passanger side dash, to under the seat to see if that makes a difference unless you all can make an other suggestions.

[HGB]

1)At this time may I suggest different RCA (phono) cables. Lousy shielding could certainly be an issue.
2) Another thought, sometimes a relay connected to the ignition wire to the radio will trigger the relay when it's turned on. The relay would have a new power source connected to it on the other end. When the relay closes, the amp will be powered by a completely different power source. It gets a bit involved here yet still doable. Just be forewarned and that should be self evident, that no cable connections will be exposed that could ever short out somewhere while experimenting. The sparks that a little 12 Volt battery can produce are quite high as you probably know.

Good Luck,

HGB

[mellowtoad]

SOLVED!!!

My AVIC system has both a RCA Rear Output and a RCA Front Output, as well as RCA Sub Outputs. These three output sets are connected to one connection that plugs into the back of the AVIC. I plug my RCA cables into the correct Output.

I was fildeling around with the back of the unit trying to figure out what was causing the issue, when I found that if I touched the rear RCA cable output to the metal of the AVIC unit, the hum went away. Perplexing, but it works. I wrapped some exposed speaker wire around the head of the rear jack and soldieried it to the unit. Issue resolved.

Anybody know how the hell this fixed this?

Thanks again for everybody's feedback!

[fastturb]

ground loop