Alternator / Stereo Interference - Team Camaro Tech
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post #1 of 20 (permalink) Old Jan 19th, 09, 04:18 PM Thread Starter
 
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Alternator / Stereo Interference

So after looking through the archives, I have narrowed down the souce of my stereo whine/interference. Here are some specs on the system as background:

105 Amp GM Alternator (for a 1987 IROC 5.7L I believe, it was a CHP feature article reccomendation for high-amp factory alternator).

Panasonic head unit

Infinity 6x9 Speakers

Pyramid 250 watt amp



Trying to get rid of the problem about 2 years ago, I installed a heavy-duty filter on the main 12v power souce to the head unit. This seems to work for the first minute or two that the car is started, but then it seems like the filter "loads up" and the stereo whine becomes present.

This weekend, doing some troubleshooting, I disconnected the alternator, which completely eliminated the problem, so I am pretty sure that is the problem, rather than plug wires, plugs, etc.

Now, I am trying to find a solution...

Can I install a filter on the main power line between the alt and the battery? Any reccomendations for one? Any other possible solutions that you would reccomend?

The stereo in this thing sounds great, but the whine is driving me nuts!

Thanks,

Dan
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post #2 of 20 (permalink) Old Jan 19th, 09, 04:40 PM
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Re: Alternator / Stereo Interference

It sounds like you're not getting power straight from the battery, but instead from another source on the vehicle. The benefit of binding to the battery (with proper fusing) is that the battery acts like a big capacitor to remove alternator whine and other noise.

I suspect what is happening is that when the battery is taking a charge, it's suppressing the alternator whine, but when the battery is charged up, you're picking up alternator noise from your connection point or ground.

My advice is to connect suitably large wire directly to the battery for both power and ground. Install fuses in both leads near the battery. I like to use those large ATO style fuse holders with the rubber cap to keep out water and dirt. While it isn't technically necessary to install a fuse on the ground lead, doing so will prevent a power amp melt-down if another ground point fails which would make your power amp a substitute ground. The ground fuse hopefully will pop before the foil traces on your amps PCB vaporize. Imagine what would happen if your power amp suddenly became a ground pathway for the starter motor or electric fans etc.

Dave
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post #3 of 20 (permalink) Old Jan 19th, 09, 05:49 PM Thread Starter
 
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Re: Alternator / Stereo Interference

Dave,

Power from the head unit is coming off of the main fuse block under the dash, both keyed and full time power (Red and Yellow leads).

The power for that amp (that runs my 6x9's) is from a 8 guage wire run to a fuse block in the trunk. It is fused at the battery with a sufficient fuse, and it grounded to the trunk pan (I am going to check this ground this weekend, but I believe it is sufficient as well). It is also fused again at the trunk, because I have other accesories (lights, 12v aux, etc running off of that block).

My other amp, which runs my subwoofers, is also coming directly off of the battery, has the proper fusing, and is grounded as well. It hard to tell if I am getting the same whine at the subs, due to the high and low pass filters installed on that part of the system.

I think I have followed industy 'best-practices' for getting power to the amp, as well as the deck, but am open to more suggestions if that is what others think may be the problem.

Thanks,

Dan
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post #4 of 20 (permalink) Old Jan 19th, 09, 06:49 PM
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Re: Alternator / Stereo Interference

Visit your local TV repair or neighborhood geek and use an oscilloscope.
Measure the amount of AC ripple on the BAT terminal.
Compare to another car; could be a leaky diode.

As Dnult suggests, battery makes for one helluva filter, until its charged up, less current going to it.

The next best ripple filter I've seen is in a Tek o-scope power supply - and one I'd like to duplicate - they take the AC ripple, delay it by 180°, then add it back in - it self-cancels.

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post #5 of 20 (permalink) Old Jan 19th, 09, 07:55 PM
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Re: Alternator / Stereo Interference

Everett has some good suggestions. A bad diode in the alternator will add a lot of noise and still appear to work fine. An O-Scope is an excellent way of seeing the noise, though it's not a commonly available tool for most folks.

Noise gets in through one or more of three ways 1) Through the power feed 2) the ground, or 3) through the input signal lines.

Sounds like your power is in pretty good shape from what you describe. I typically use both a power and a ground wire though - even though the body is electrically grounded. I'm not convinced a separate ground will solve your problem though, but it's worth doing an experiment.

Here is the theory behind running separate power and ground feeds. See if it doesn't give you some ideas based on what you know about your setup. When parts of a circuit (power and/or ground) are shared between different loads, the loads on that circuit affect each other. It's kind of like a shower that suddenly gets cold when someone flushes the toilet. Bigger loads draw more current and have a bigger coupling affect.

Now, think about how all the electrons in your car body are getting back to the battery. Usually it's through a little pig-tail wire connected from the battery (-) to the right fender. All of the body electrical currents return through that same wire, and any noise created by an element of the circuit will be reflected into the other loads on that same circuit (the old toilet and shower delima). Having a separate ground will help keep the noisy stuff away from your audio equipment.

If it's practical to temporarily hook up a temporary ground from the battery to the amp, give it a try. Even an old extension cord rigged up to complete the circuit would be worth the experiment. You might also try running a temporary ground from the head unit back to the amp and see if the noise subsides.

Are you running line level signals from the head unit to the amp? Line level signals require more amplification (although the audio will have a better signal to noise ratio). Inferior cables carrying the line level signal can amplify the noise problem. Line level cables should be / are shielded. Some of the shielding on the cheaper cables aren't very good. If it's easy to change your setup to use speaker level outputs from your head unit, you might give that a try - it may reduce the noise problem some and help isolate the noise to the amplifier input. If the noise is coming from the input, try some different input cables.

Beyond this, you'll probably have to resort to adding filters in various places to try and squelch the noise. I'd avoid jumping to the filter route though until I was certain all the other possible issues have been resolved. Filters attentuate noise, but they won't eliminate it.

Keep us informed. Noise problems can be difficult to isolate and eliminate. Hopefully this will give you some ideas and help you determine if the power, ground, or amp input are the source.

Dave
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post #6 of 20 (permalink) Old Jan 19th, 09, 11:22 PM
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Re: Alternator / Stereo Interference

Sounds like a bad ground for the amp or stereo. Match your ground on your amp to the size of your power cable. Make your ground runs as short as possible. Do not run speaker wire and RCA(patch cables) along the same route with power cable. Put them on the seperate side of the car. If they should intersect the power cable, then it should only be in 90 degree intervals. Also, use good quality wiring. This is especially important with RCA cables. The cheap autostore or walmart rca`s aren`t going to cut it. You must splurge when you want something done right.

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post #7 of 20 (permalink) Old Jan 20th, 09, 10:08 AM
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Re: Alternator / Stereo Interference

Who installed the amplifier? If the RCA cables for the amp are run down the same side of the car as the power wire, that is the reason for your whine. The RCA cables need to be isolated COMPLETELY from the rest of the system wiring, including speaker wires. Run the power, remote turn on and speaker wires down one side and the RCA's down the other side of the car.

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post #8 of 20 (permalink) Old Jan 20th, 09, 01:17 PM
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Re: Alternator / Stereo Interference

Either a bad ground or as Everett says faulty alternater...well not faulty as it still works but something inside is on its way out, a diode or maybe a bearing.
Had this issue yrs ago, and connected a supressor capacitor across the back of the alternator....eventually the alternator slowly died...wear and tear, rebuilt it...brushes and bearings, no capactor and fine ever since...for the last 10 yrs.

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post #9 of 20 (permalink) Old Jan 20th, 09, 09:16 PM
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Re: Alternator / Stereo Interference

Good suggestions on wire routing, that's definately a possibility. You'll probably find there are two or three things that contribute to the problem and incrementally you can make it better.

Dave
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post #10 of 20 (permalink) Old Jan 21st, 09, 11:25 AM
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Re: Alternator / Stereo Interference

I seriously doubt the alternator is bad. If the RCA wires ARE NOT ISOLATED, that is your problem. Run the RCA's down one side of the car and run ALL THE OTHER wires that relate to the stereo down the other side. The RCA wires can actually grab any signal near it and amplify it. When that happens, it comes through the speakers as a high pitch wine that increases and decreases with engine RPM.

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post #11 of 20 (permalink) Old Jan 22nd, 09, 05:48 PM Thread Starter
 
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Re: Alternator / Stereo Interference

RCA cables are isolated from all power cables, with power running down the driver side, and RCA's on the passenger side. I am going to double check all of the grounds this weekend, and will report back on my progress. Otherwise, I may try to swap out the alternator and see if that is the issue. If none of that works, I don't know where I will go from there. All of the stereo installation was done during the restoration, and rewiring the car just isn't really an option at this point, its all under the carpet and would be a major P.I.T.A to re-do.

Thanks for all the help, I'll let you know if I make any progess.

Thanks,

Dan
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post #12 of 20 (permalink) Old Jan 22nd, 09, 08:46 PM
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Re: Alternator / Stereo Interference

Another problem you may have is possibly the gains on the amplifier are set to high ?. If they are set too high the volume control is very touchy. In other words at very low volume you hear some music with a fair amount of background hiss and then by just barely turning up the volume control you get maximum volume out of the system.
To correct this, back down the gains to where when the volume is up about 3/4" the way to full the amplifier is putting out all it can.

Another problem could be compadibility problems. Brand A radio with Brand B Amplifier(s) can give you alternator noise issues. Panasonic is decent but Pyramid to me is a pretty low quality of product. Some may rave about Pyramid but a lot may say other wise. Try swapping in a different brand amplifier (and check the gain setting on it too) to see how this affects your problem.

Another thing you can try is take a small gauge wire and ground one end and then touch the other end to the outside barrel of the RCA cables. Try this at the radio end, then at the amp end, and then both ends. Another "filter" type is a ground loop isolator with 2 female RCA ends and two male RCA ends that goes inline on your existing RCA cables. This too needs to be tried at both ends (by the radio and then by the amplifier). These ground loop isolators also have ground wires out of them that sometimes need to be grounded and other times left ungrounded.

If all else fails, take your equipment and temporarily wire it all together right next to your battery and wire it directly to the positive and negative posts to see what happens and then if it's still there, try this temp setup on another car.

I've had many a phone call about a person wanting a noise suppressor and sometimes the system needs it, or sometimes there is a problem with the install or the vehicle.

Another thing is try disconnecting the antenna lead on the radio. This cable is a two conductor with one conductor being a ground and if the antenna is grounded onto let's say a fender and it is not the same potential as the rest of the grounds in the car the noise might be getting in this way.

I've not seen fried RCA grounds on Panasonic radio's before but have on Pioneer radio's but it's possible this might have happened on your radio.

Jim

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post #13 of 20 (permalink) Old Jan 23rd, 09, 04:12 AM
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Re: Alternator / Stereo Interference

Jim(SOA-Nova) brings up a good point - shielded audio cables have the shield grounded at one end of the cable, the other end is left open.
Reason being this prevents ground loops - filters out interference from primary power - more of an AC power fix than DC power.

And good suggestion to adjust gain AND to try the system in another vehicle and listen to the results. I'm willing to bet its either a bad alternator, poor wire connections, or a missing ground strap/wire. The battery is a good ripple filter.

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post #14 of 20 (permalink) Old Jan 23rd, 09, 01:59 PM
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Re: Alternator / Stereo Interference

It looks like all angles have been covered.
As a ham opperator we use to make torroid coils for interference troubles but they are so cheap it don't make sence any more.
Shielding,Grounds ,propper wire size ,Not running feed lines near speaker lines all sound good, Bad alternator diode sounds a lot like the problem.
If all else fails put my x wife in the car with you her whinning will drown out any thing!!!
good luck
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post #15 of 20 (permalink) Old Jan 25th, 09, 10:12 AM Thread Starter
 
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Re: Alternator / Stereo Interference

I did some work on the grounds this weekend, and I think that is what solved the problem. At the same time, I replaced the Pyramid amp with a Rockford Fosgate Punch125.2, which should drive the speakers even better.

Between the two solutions, the problem is gone, as far as I can tell.

Thanks for the help guys!

Dan
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