alternator engine noise

[Chupa]

ive tried everything. im out of ideas. hers a run down of the things ive tried with the result..

tried a diffrent amp... noise
tried using RCA cables from the HU to the amp, out in the open... noise
tried muteing plugs on the amp... no noise
tried a diffrent head unit... noise
changed gnd 3 times, all of which were directly to the body, all of which i grinded before i connected it to make sure there is good contat... noise each location
tried a speaker connected right to amp ( not routed through the truck)... noise

i think thats all the real important things ive tried. any other ideas would be great... thanks

[SupraGuy]

The first thing that I tend to check is just how bad the electrical system is. You can see about audio frequency noise in an electrical system using a rather simple device. You can use a capacitor (3.3uF works well) some wire, alligator clips and a set of cheap PC speakers. Connect the PC speakers to the battery through the capacitor. The capacitor prevents the DC voltage from blowing the little amp in the PC speakers, but allows any audio frequency fluctiations to pass, which get amplified so that you can hear them. If this is really bad, then your electrical system needs help.

Even if not, a good system should have pretty decent noise rejection, where it's not a big problem.

1. If the electrical system is really bad, check that the battery connections are solid, and that the alternator is in reasonable shape. Check the battery ground cable as well, this is an often overlooked source of problems.
   
2. Disconnect all input sources from your amplifier, and start the car. Listen for alternator whine. If you've got it, then start checking your amplifier power and ground to ensure that they're solid. The ground should have a good connection to a solid part of the car's chassis. The power connection should go directly to the car's battery positive (+) terminal, with only a fuse block (near the battery) in the way. Possibly a distribution block and/or stiffening capacitor as well.
   
3. If it was quiet, then connect the input cables to the amp, but disconnect them at the head unit. If this introduces noise into the system, you need to look at how your signal cables are run, or possibly the quality of the cables being used. Running the signal cables parallel to a power wire (Like the amp power) can cause rf noise to be picked up and amplified by the amplifier. Move the cables to a location further away from noise sources.
   
4. If it was still quiet, connect the head unit, and play a zero bit track (silence) at low volume. Try adjusting the volume, and see if that changes the noise level. If the noise remains constant, then the problem is in the output of your head unit. If it goes up and down with the volume, it's in the signal. Regardless, this is likely to be a poor power or ground connection to your head unit. Believe it or not, the factory power and ground wires for most manufacturers provides very clean power for the head unit. There are very few cases where you get alternator whine from a factory deck, and there isn't a problem with the alternator. Using a quality wiring harness adaptor for your aftermarket head unit generally provides excellent results.

A vast majority of noise problems are ground problems. Make sure that your system grounds are solidly connected to the chassis, and you'll be fine. Much has been made of the "common ground point" idea, but in car audio this is often impractical or impossible. For all practical intents and purposes, the resistance within the car chassis itself can be assumed to be zero, certainly it's going to be less than the resistance of a piece of wire that leads from your head unit to your trunk.

HTH
SupraGuy

[tsmith1315]

Noise, noise, noise. Frustrating isn't it?

What kind of truck? Some vehicles are more prone to alternator noise. Mid-80's Ford trucks were, if my old memory is functioning correctly.

First, disconnect the RCA's from the amp. Still have noise? Probably not. The simplest way to solve the typical ground loop problem this test would indicate is with a ground loop isolator. Find one that uses transformers. Scosche made decent ones when I was installing. Yes, it's a band-aid. But they are very easy to plug in, they usually work, and without appreciable reduction in SQ. Shoot me for using them, but too often it was just: plug one in, noise is gone, you're done.
You can try cutting a cheap RCA patch cable a foot or two from one end, strip back the insulation and reconnect the center conductors. Leave yourself plenty of bare copper shield hanging loose and experiment with those, one end at a time, starting with the side going into the amp. For example, try grounding it to the head unit chassis instead of the RCA out shield. Usually this will increase noises significantly, but there are always surprises in car audio.

To troubleshoot noise an old-fashioned way...

-Remove the head unit from the dash and lay it on the seat (or on top of the dash, wherever it's not touching metal.)
-Unscrew the amp and position it so the heatsink isn't grounding against anything.
-Remove the headunit ground, and re-route it to the same point the amp is grounded using heavy (14, 12, 10) gauge wire. You can just use a ring terminal on the wire and screw it to the head unit's case.
-Unplug the antenna lead (it's grounded, too)
You now only have one ground point for the entire system. Power it up and listen...

Still noisy? Probably not, but if so:
-Explore other ground points, lots of them. Break the rules, get a nice long ground cable, strip an inch or so of insulation and go to town.
-Run a battery cable around the outside of the cab,
-Try a good LC filter on the head unit power lead.

Is it quiet?,
-reconnect the antenna and listen. Still quiet?
-position the head unit back in the dash, but don't reconnect the old ground wire, and listen. Still quiet?
-actually mount the head unit in place, but don't reconnect the old ground, and listen. Still quiet?
-Remount the amplifier and listen.

One and only one change at a time, working methodically from one end to the other until you have the problem identified and reduced. It's the only consistent way to track down noisy culprits.

Tim

[2pist]

Wow, you guys have some excellent ideas. I'm glad I read this thread!

[rkc7]

I'd check to make sure your signal cables aren't near any power cables first... I made that mistake, and was dumbfounded (this was before I knew as much as I do now) when I tried a ground-loop isolator and still didn't do anything. Well, I eventually figured it out, ran the cable way far away from the power (or ground) and TADA!

[95Honda]

All grounds (every one of them!) need to terminate at the SAME place. Heavy wire..... Heavier the gauge of ground wire (for everything, again) The less voltage potential you will have on all of your signal cables (shields or [-] side).... Sometimes it is a lot of work, but it will solve your problem 99% of the time if you don't have defective equipment. Ground loop isolaters may work, but they always degrade the sound.....

Keep signal and power wires seperate, if they need to cross, do it at 90 degrees.

Like mentioned earlier, antenna is also a ground, may have to disconnect it. Most car audio gear is designed to run off DC voltage with some ripple, so alternator "noise" isn't nessesarily a bad thing, just keep it out of the signal chain.....

Good luck!

[SupraGuy]

95Honda: Terminating all grounds in the same place isn't always possible, and certainly isn't needed in a vast majority of cases.

If you have a solid ground to the car chassis, then NO wire no matter how thick is going to show lower impedance than that. The car's chassis is an excellent conductor, and if you don't think so, then you'd better start running both power AND ground for your amplifiers straight from the car battery. We all know that's not necessary, because the chassis provides a more than adequate return to the battery negative post.

Personally, I've NEVER seen moving head unit grounds to the trunk solve a noise problem. And if you have to disconnect the antenna, I would not consider that to be an acceptable solution.

[tsmith1315]

95Honda: Terminating all grounds in the same place isn't always possible, and certainly isn't needed in a vast majority of cases.

Absolutey agreed. However, it will occasionally fix the problem. And you never know when that occasion will be.

because the chassis provides a more than adequate return to the battery negative post.

Again agreed, but not all points on the chassis are equivalent. If they were, grounds loops wouldn't be a problem.

Personally, I've NEVER seen moving head unit grounds to the trunk solve a noise problem.

I have. More often I found that leaving the head unit ground in place, and just tying a wire from the case to the amp ground would help.

Personally, I've NEVER seen running power and signal cables together cause noise. That's not to say it can't happen, as rkc7 has just attested.
If I came up with noise, I would ALWAYS run another RCA around to check, because it's a quick and easy thing to check. But not once in more than a decade did I have to re-run a signal cable away from power cables.

Point being, you have to explore a motor noise problem methodically, and without prejudice to what "can't" be causing it.

[95Honda]

You would think that a car's chassis would be a perfect ground, and the frame is. But, I have gone in to fix a lot of installs with poor grounds on body panels. On a lot of new cars there is a lot of non conductive adhesive used to attach panels, with spot welds. Now I know that isn't the best place to bond a ground, and so do you guys, but alot of people don't. The last 10 or so installs I have done I used a #8 wire from the deck to the amplifiers (s) ground. I bought a bunch of it (2500') from a surplus supplier. These systems have the lowest noise floor I have ever measured. I use a H/P distortion anyalizer with the notch frequency set to the alternator's AC component at idle. It really tells you what going on. Going from 10 awg wire to 8 awg wire dropped the noise almost 1 db on a Bronco I worked on.

95Honda: Terminating all grounds in the same place isn't always possible, and certainly isn't needed in a vast majority of cases.

-It is always possible, it's just is it worth it for that last db or so of noise drop..... For most people if they can't hear the wine with the engine running and background noise they are happy with it....

It may be over-kill, but it is the way I do things....

If I can get the grounds terminted directly to the frame, or a major structural junction in a uni-body car, that usally works quite well also.

Also how well is the battery/charging system bonded to the cars frame? Most cars are bonded very well to the block (most current to the starter) but have a lesser ground tied to the body... That also makes matters worse.... The car may be a great conductor, but if it isn't bonded with a low resistance ground to the battery/charging system then you have another problem.... Anyway I'm rambling, just my thoughts.......

[Chupa]

ahhh, i cant figure this out.

i use muteing plugs and i get no noise. but if i plug in a RCA cable... just to the amp. and just let the wire run outside the car, connected to nothing, i get noise. Its high quality twisted fosgate RCA cable.

that help anyone think of soemthing else i could try?