Garmin 396 and alternator noise - help?

markscogg · #1 05-19-2007, 06:36 PM

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).

Walt · #2 05-19-2007, 07:07 PM

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.

N112B · #3 05-19-2007, 07:07 PM

Quote:

Originally Posted by markscogg

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).

Mark - I had the exact same problem. The problem went away when I upgraded to a 496. Yes, that was the fix!

Tandem46 · #4 05-20-2007, 09:33 AM

Walt,

Do you have a part #/photo of the isolator you bought from radio shack?

thanks

Walt · #5 05-20-2007, 10:13 AM

Tobin,
This is the one I got from Crutchfield (not radio shack)
http://www.crutchfield.com/S-Twa17Em...sp?i=127SNI135
Also you should really isolate the two channels using a couple of resistors (150 ohms) in each leg before tying them together for the the mono input.

markscogg · #6 05-20-2007, 06:12 PM

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 ;-)

Walt · #7 05-20-2007, 08:32 PM

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.

Tandem46 · #8 05-20-2007, 08:44 PM

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,

Walt · #9 05-21-2007, 06:47 AM

Quote:

Originally Posted by tobinbasford

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.

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.

Ironflight · #10 05-21-2007, 07:12 AM

Quote:

Originally Posted by Walt

So if you need an isolator let me know. .

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