GPS496 scratchy audio into GMA340 audio panel - ideas?

[IowaRV9Dreamer]

I have a GMA 340 audio panel in the Skipper with a panel mounted 1/8" audio jack. I use this jack all the time with my iPod and have no troubles.

This weekend I decided to plug in the 496 audio and have a listen. I did get it to work, but it was very low level and highly distorted / scratchy. I was able to hear both the XM Preview channel and the terrain alerts. I got the audio from the 496 via the jack on the back.

I connected the 496 to the panel jack through an audio isolation transformer from cables-to-go.com, link here. I haven't yet tried the 496 without the transformer.

To rule out any problems with the audio isolation transformer, I tried it with the iPod. The transformer had no effect.

I looked in the 340 install manual, and it appears to have a stereo input, and I assume the 496 has a stereo output.

What am I doing wrong here? Is there some secret setting in the 496 that will help?

I'm working audio wiring on the RV now, and would like to understand this as I plan to wire the 496 audio in the RV.

 

[Walt]

What am I doing wrong here? Is there some secret setting in the 496 that will help?

I'm working audio wiring on the RV now, and would like to understand this as I plan to wire the 496 audio in the RV.

Check that the audio output in the "sound setup" menu is set to "headphones" not "line".

 

[noelf]

I seem to recall that the audio panel has a selectable HI / LOW select for the music input. This is to better match the output level of the external device(s) with the input level expected by the audio panel.