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DaveLeonard wrote:
Now that the engine is running well, I have a new problem. Alternator
noise. The intercom is the main problem (victim). When the intercom the
alternator noise is quite noticeable, even annoying. The noise goes away
altogether when the intercom is off (i.e., when using the radio without the
intercom/audio panel). If I turn off the alternator the noise mostly goes
away, (I think the coils make a faint noise - but it is not significant.)
The intercom/audio panel is the kit from RST.
I was going to try an automotive filter on the power to the intercom. Any
other thoughts/suggestions?
You should probably ask this on Aeroelectric too, but alternator noise in audio systems is caused by a ground loop SO often that it's a good place to start looking. Audio cables usually have shields and the shields are usually connected to ground on both sides, so electrons have two paths to flow back through (ship ground and audio cable ground). If one of the paths has a slightly different resistance than the other (and they almost invariably do) you get a ground loop, and your audio cable becomes a huge antenna pulling in your alternator noise.
The power filter might help but it's usually designed only for noisy power lines and there's a good chance you're picking this up "out of the air" so to speak. Another thing you might try is an isolation transformer, which actually breaks the ground loop. Crutchfields carries one that I happen to know works, because I have it in my wife's car:
http://www.crutchfield.com/S-TmeALbDgWvx/cgi-bin/ProdView.asp?i=127SNI1&search=isolator
For $14.99 to try it out, and given their good return policy, it's a low-risk test. You'd probably have several places to try this - either on the input(s) to the intercom, or the outputs from it. I DO recommend the one above, by the way. I tried three of them before I came across it, and the first few were awful.
If you want the REAL solution you need to break your ground loop, although this can be tough. Good grounding practices are a must in audio wiring. Every device should have its own ground connection and they should all be run to a single location. DON'T daisy-chain a ground connection from one audio device to another. Also, if you are using shielded wiring, don't connect the shield on both ends, just on the "source" end. Mount headphone jacks on insulating brackets so they don't ground to the local airframe if yours is aluminum. Etc.
Go Google for alternator noise and ground loops and you'll find a bajillion hits, all of which basically come down to "good luck, even experts can't always find them." The filters are the easiest solutions.
Regards,
Chad
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