olddog

iTrader: (2)

I have finally completed my audio install but am still getting some alternator noise which i only hear when music is low. i can tell it is alternator noise cos it rises and reduces with the RPM level.When i turn audio off on my deck(eclipse unit has the ability to just turn audio off and leave nav on, it stops but when i mute music, it is still there. Also when i pull out the RCAs from the amp it also stops.
I have searched and changed the RCAs and all grounds are to frame(i think). (the trunk i used the bolt which holds the shiny metal thingy down (the one that keeps the carpet in place) and in front, i used the frame which the stock cd changer was bolted onto in the glove(i had to extend wire to that location.
BTW, before adding amp, i powered the speakers with the a/market unit and there was not noise.
from all this, i have 3 questions,

1. (Weird thing first) I joined the ground wire and the parking brake wire from the unit together(so i can watch dvds on the move and hoping to ground them at the same spot) and even when i don't connect these two to any ground source, the unit still functions as though both wires were grounded i.e dvds can be viewed while driving and unit functions. Isn't the unit supposed not to function if not grounded? or is the ground pulling its "ground from the parking brake wire it is co-joined with?

2. Can a/market installers tell me where they grounded their units to in front( i could barely find any frame when unit is pulled out in front) and where they also grounded their amps to in trunk.

3.also has anybody had any luck with alternator noise filters or ground loop isolators?


sorry for the long story guys and thanks for any inputs or advice given.

GS FONZy

iTrader: (6)

1. the unit is grounding from the metal braket that holds it in place and there is nothing wrong with both ground in that spot. mine are the same way, unit ground, parking brake and bypass flasher.

2. my amp is grounded just a few inches away fron where it's located in trunk. i circuled the ground on pic and i just used a very short self tapping screw to ground in to body.

3. the problem i often see with engine noise has to do with cheap rca cables. i have my power cable, remote and rca cables running in the same location and i have no problems with engine noise. get some moster rca cables and that should take care of that problem.

olddog

iTrader: (2)

thanks man.
i got some ground loop isolators and hooked them to the speaker RCAs going into the amp and the noise disappeared.
when i hook my amp to its proper location, i will make the ground shorter and see if that was the cause.
thanks

TurboES300

Mine is grounded in the same spot..looks like he beat me to it...enjoy the system!!!

engin_ear

iTrader: (1)

You definitely had a ground loop (multiple, different ground paths), unfortunately. If the ground loop isolators took care of it, you're good to go! The ground path via the shield of the RCAs was different from the ground path of the amp ground in the trunk. This usually causes these kinds of problems.

One thing to note - your system is not very complex (basically headunit + amp(s)), so ground loop isolation at the amps worked. For those with more signal processing units and more complex systems, EVERYTHING should be tied to a single-point ground (I typically use a terminal block for this, or big honkin' power distribution block). This single point ground should have a minimum 8ga directly to the battery negative post, and all ground to equipment should be kept as short as possible. Generally, it is not practical to ground rear-mounted amps to the same point in the front of car, so a solid ground to the body in the rear will suffice.
Even with the above scheme, the RCA shield (signal) ground vs. the single-point (power) ground can often cause problems. I just had this problem in my current install, and the noise didn't go away until I put one of the processors in floating-ground (isolated) mode.

Jerry

olddog

iTrader: (2)

but isn't extending the ground wire of the unit from the front to wherever the supposed ground should be going to leave the unit susceptible to engine/ alternator noise. Reason i say this is because everybody has always said ground should be as short as possible.

engin_ear

iTrader: (1)

yes, ground should be as short as possible, true. That doesn't necessarily mean "short" in all cases, it just means "as short as possible".

What matters most is the IMPEDANCE of the ground (of which its RESISTANCE is a major component). This is why grounds need to be as short as possible, and also of a large enough gauge of wire or metal that the impedance is kept to an absolute minimum. Engine/alternator whine is introduced more from multiple ground paths that differ from each other (to the same piece of equipment) than from the length of the ground itself.

"BODY" GROUND is not really the ground that it is assumed to be. An ideal ground has 0 impedance, and thus 0 resistance. But due to ALL of the currents flowing in the body metal from every electrical/electronic device in the car, and the fact that it is not one huge piece of metal, and is made up of various chunks, with less-than-optimum physical connections between the chunks (and often with an anti-corrosion coating), the body ground is not all at the same 0 voltage all of the time, everywhere. This allows return currents and other nasties from other devices to couple into the audio circuits, if and when the conditions are right.

ALso remember that every electrical circuit must form a full circuit, from internal battery ground, to positive battery post, back to negative battery post and internal battery ground. So even though you ground an amp to the body in the trunk, the return current for its circuit must travel thru the body metal and back to battery ground, which is where the amp's current source originated. The best ground for an amp in the trunk is actually a 0-gauge wire that runs directly back to negative battery post, avoiding all contact with body metal. But for most installs this is impractical. And the fact that there are both signal and power grounds to worry about is a more important problem. Because of this problem (which has to do with how grounds are handled INSIDE each piece of equipment, on the circuit board(s) and connectors), you can make all of the device "grounds" each only 1 inch long, but still have ground loop problems and alternator whine.

Back to the short ground thing, any "ground" can only really be as short as the distance between the power supply for the circuit (in this case, alternator & battery) and the equipment itself. Even if you attach a short wire to a 'grounding point', the return current still has to flow back to the source, and extra resistance, capacitance, and inductance between that point and the battery can cause noise voltages IN THE GROUND.

Another problem you get into is inductive coupling of loop currents in each circuit, which can cause completely independent circuits to couple into each other. But that's another ugly story....

Jerry

olddog

iTrader: (2)

nice lecture engine-ear
am going to have to tap your brain one of these days.
when i have the chance am going to take out the ground loop isolators and try to make the connection come through without no engine noise.
some might ask,"olddog, why go through all that if the ground loop isolators have fixed your problem?" the answer is self-fulfillment and achievement
if others can achieve pure sound wihout engine noise, i can

engin_ear

iTrader: (1)

I applaud your motivation, but you may not get rid of the noise without the G/L isolators. Remember what I mentioned above about how signal vs. power grounds are handled inside the individual pieces of equipment. You cannot change this easily, without hacking up your headunit, etc. I'd just leave the isolators in there and fuggettabboutit.

olddog

iTrader: (2)

so, how about people who have the same units as mine and not getting any noise.
are you implying that the structure compilation of the unit itself plays a keyrole in the "setup"?

mitsuguy

iTrader: (2)

what I did to troubleshoot a problem like this is to take a cd player or mp3 player and some headphone to rca cables, and hook them into separate spots in the audio system... Start at the amp, plug the mp3 player directly into the amp, car running, and play some music... what do you hear? no noise, go to the next piece of the system, eq or whatnot... still no noise, hook them into your patch cables at the front of the car... still no noise, well, you're in my boat... Mine was the in dash processor causing the noise... After implementing a better than stock ground, and using a small .1 farad capacitor inline, my noise went away... was definitely a bugger to find though... no matter what you find as the problem, it is more than likely the ground as everyone else has stated - just use my process to find out which component is causing the problem...