Static on music aux-in

[yachtjim]

Since I bought my plane I have not been able to get music to play through the intercom system. It is driving me crazy. I have tried a gound loop isolator, that doesn't work. I have replaced and rearranged wires. Nothing works. I can hear music, but there is lots of static. My source is my garmin 796 and xm. Here are some weird things I notice:

1. When the 796 cig lighter plug is fully plugged in there is bad static. As soon as I back out the plug a bit so the center (positive) conductor of the plug separates it works perfect. But then I get no power to the 796. If I back the plug all the way out so negative disconnects then I get nothing. No music but I do get super loud static. Louder than when its fully plugged in.

2. If I try to connect my cell phone as the source to the aux-in I get super loud static and can't hear anything else.

The only thing I haven't tried is to switch the actual leads on the aux-in itself. Do you think if the leads were backwards on the aux-in receptacle it would cause these problems? How would it have been signed off on when installed if it never worked?

These problems happen with and without the engine running so I don't think any of the static is alternator related.

 

[gismo]

Since I bought my plane I have not been able to get music to play through the intercom system. It is driving me crazy. I have tried a gound loop isolator, that doesn't work. I have replaced and rearranged wires. Nothing works. I can hear music, but there is lots of static. My source is my garmin 796 and xm. Here are some weird things I notice:

1. When the 796 cig lighter plug is fully plugged in there is bad static. As soon as I back out the plug a bit so the center (positive) conductor of the plug separates it works perfect. But then I get no power to the 796. If I back the plug all the way out so negative disconnects then I get nothing. No music but I do get super loud static. Louder than when its fully plugged in.

2. If I try to connect my cell phone as the source to the aux-in I get super loud static and can't hear anything else.

The only thing I haven't tried is to switch the actual leads on the aux-in itself. Do you think if the leads were backwards on the aux-in receptacle it would cause these problems? How would it have been signed off on when installed if it never worked?

These problems happen with and without the engine running so I don't think any of the static is alternator related.

Sounds like (NPI) the jack is either wired wrong or isn't isolated (mounted in metal without insulating washers) or both.

 

[rottydaddy]

By "static" do you mean "frying bacon" (or "hiss")or "hum"? No offense, but as an audio troubleshooting guy, I have heard "static" used to describe just about every audible anomaly in sound systems.
If it's "frying bacon" or "hiss" (which is what "static" means) the most likely culprit is dirt or grease. Might be in the audio connectors, might be in the power socket.

If it's hum, you have a ground problem. The electrons are pinging back and forth across the circuit because there is more than one good path to ground available, and they can't make up their minds. The rate at which they do this determines the pitch of the hum, which any speakers in the system will reproduce as sound, if it's within the frequency range of the speakers. If one of the available paths to ground is on the positive side of the circuit, you might get nothing but hum (which sounds a lot like what you are describing).
Having positive and negative flipped somewhere might cause this, but it might not.
But you mention pulling out the power plug so that the "hot" pin is no longer making contact, yet still seeing the device work... that's weird, and yes, it could mean the polarity is reversed somewhere... or even a short between positive and negative. If you only have this problem when using the aux in on your portable comm box or intercom panel with your cellphone, there may be a short in the phone adaptor cable, or its wiring is not compatible with the box. If plugging anything into that aux input gives you hum, it's a problem inside the box or panel, most likely at the connector. Gismo is right about the jack itself being mounted without isolation... but sometimes that's the way it should be done. Ground hum seems to defy electronic laws sometimes... often it comes down to experimenting until the hum goes away.
It might also be a a gain structure issue. Hum is always there in the "noise floor", along with static, and if you have the phone's output and the aux input volume settings set up wrong relative to each other, that background noise may be amplified to the point where it competes with the audio signal itself.
But given that fiddling with the power plug can make it come and go, it's probably more likely a ground problem. If this cable carries power as well as audio, it's most likely the power circuit. But sometimes audio gear has audio and power sharing the same ground directly, which can make the whole system less "fault resistant".

 

[Skylane81E]

Easy quick and common problem.


Check that the power jack is tight, they tend to work loose a lot

 

[rmlewisjr]

I had a problem similar to this with my 696. Found that the lighter plug ground was loose. Tightened it up and the noise went away. Bottom line it’s being induced via the power plug. (It stops when you are on internal battery starts when you plug it in.) Make sure that you have good grounds to the lighter plug.