What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Garmin 396 and alternator noise - help?

M

markscogg

Well Known Member
Just installed an "audio in" for my new 396 and it is picking up alternator whine. Goes away when the 396 is unpluged from ship's power. Gets louder as I turn on more accessories?
The 396 is wired with a Garmin power/data cable. Power, ground and one wire to autopilot.
I installed 2 mini headphone jacks. (one for passengers to use with iPod).
Used shielded wire and grounded the shield. Jumpered the left and right stero channels, as the intercom in mono (PS Eng. PM501).
 
The 396 needs isolation on the output...

due to the ground method they use on the audio output. I picked up a little mini stereo isolation transformer (has mni plugs on each end) from radio shack and all is fine now.
 
markscogg said:
Just installed an "audio in" for my new 396 and it is picking up alternator whine. Goes away when the 396 is unpluged from ship's power. Gets louder as I turn on more accessories?
The 396 is wired with a Garmin power/data cable. Power, ground and one wire to autopilot.
I installed 2 mini headphone jacks. (one for passengers to use with iPod).
Used shielded wire and grounded the shield. Jumpered the left and right stero channels, as the intercom in mono (PS Eng. PM501).
Click to expand...
Mark - I had the exact same problem. The problem went away when I upgraded to a 496. Yes, that was the fix!
 
Noise filter

I ordered the noise filter from Crutchfield. That looks like the best way to start.
The 496 idea may have to wait....
Thanks for the help.

From Rosie: I bought this same filter for cancelling the slight noise I have with my XM radio and it worked perfectly ;-)
 
Last edited by a moderator:
You really need to isolate the channels

from each other with the resistors, the music will be distorted as the stereo channels work against each other. You can pick up the resistors at RS for a buck or so.
 
Walt,
I'm not following you on the resistor thing. Are you talking about pulling the unit apart and adding resistors? I have the 396 connected from its audio output jack on the back to an input in my ics. I don't have the audio wire on the power/data cable connected.
thanks again,
 
Stereo output to mono input...

tobinbasford said:
Walt,
I'm not following you on the resistor thing. Are you talking about pulling the unit apart and adding resistors? I have the 396 connected from its audio output jack on the back to an input in my ics.
Click to expand...

No internal mods... you need to modify your stereo cable is all. The resistors go in series with each of the stereo outputs. If you cut the cable and peel back the shield you will find the two wires, cut them and insert a resistor inline with each wire. It may be easier to but 2 cables with a plug on one end and pigtails on the other and connect them with the resistors (tie the shields together) rather than trying to cut and splice a one piece cable. I also removed my isolator yesterday and things are fine (the 496 doesn't need it). So if you need an isolator let me know. Just to clarify, the resistors are only needed when tying the stereo outputs together for a mono intercom.
 
I'll try it!

Walt said:
So if you need an isolator let me know. .
Click to expand...

Hey Walt, I almost ordered one last night when I saw your post - if you want to get rid of yours, I'll take it! I am tired of the whine when I have my 396 plugged in to power and I'm trying to listen to music....faint, but annoying.

Check your PM...

Paul
 
For the electronically challenged..

Walt said:
No internal mods... you need to modify your stereo cable is all. The resistors go in series with each of the stereo outputs. If you cut the cable and peel back the shield you will find the two wires, cut them and insert a resistor inline with each wire. It may be easier to but 2 cables with a plug on one end and pigtails on the other and connect them with the resistors .
Click to expand...

Are we talking about modifing the cable between the 396 and the audio imput jack? Or the the wire I have to stand on my head just to see?
Thanks
 
The stereo cable..

from the mini phone plug on back of the unit. This is the output used for the music and aural warning input to the intercom.
 
It Works!

I ran into Walt at SWRFI today, and he gave me the isolator that he's no longer using, and wow! The thing really works - I used it on the flight home and was able to listen to Bluegrass on the XM for the first time without that annoying alternator whine.... :D

Thanks again Walt!

Paul
 
Should not happen..

markscogg said:
I got the isolator, but it cut the volume way down on the XM.
Anyone else?
Click to expand...

The Isolator is a 1/1 transformer and there should be no reduction in volume. The only way this would happen would be if the output load was lower than the standard 600ohm input (standard audio input load). I just took isolator out because the 496 doesn't need it and I can tell you there was no difference in volume with it in or out of the system.
 
I used the same volume settings as always today with the isolator instaled as I did without it - no volume change, just no whine....

Paul
 
Ironflight, that isolator is malfunctioning...

You should be receiving Bee Gees, Olivia Newton John, John Denver, etc.
 
You must log in or register to reply here.
Back
Top