496 into a PMA4000 music input?

Greetings,

I have a 496 that I'm feeding into the music input on a PMA4000 intercom, and I'm getting a lot of scratchy distortion when I turn the volume up above about half on the 496. I have the left and right channels tied together, which I know works fine for a 396 with the same intercom on a friends plane.

The 496 does have a different setting on the "sound" menu, where you can set audio panel, or stereo headset for the output option. It's possible they've changed something else as well.

Is anyone else using a 496 with a PMA4000? Can you turn the volume of the XM radio up loud enough to hear well without distortion?

Thanks,
Rusty

I run the 496 into the PM3000 intercom

and it works fine, until I went in and reset it to "headphone" instead of "line" output though it was overloading the input of the 3000 and was distorted.

Thanks Walt. So you're saying that it distorted when set to "audio panel", but is fine now that it's set to "headphones"? If so, that's great info.

Do you recall having to power off and on the 496 to make the change take effect? I changed back and forth between the two settings on the ground, and couldn't hear any difference at all, so now I'm wondering if maybe I have to power cycle the unit to make the change take effect.

Thanks,
Rusty

Yes that's correct

I believe mine says "Line" or "Headphone", line is a fixed output which is to high (plug this into your home stere for XM listening of perhaps some car audio systems), headphone allows you to use the volume control on the unit to contol output. So switch it to headphones and them turn down the volume and you should be good to go. I did this while flying with it the first time and the audio was horribly distorted until I found this setting. My previous 396 had no line output so this was a new one for me with the 496. PS: I do love this unit!

Thanks Walt, but I may be more confused than before. What you say makes sense, since there is a standard PP volume for audio panel items I believe. However, mine was on "line" by default, and the volume control works just fine. The problem is that the distortion starts at about half volume, which is just a little lower than I need it to be. The volume control works exactly the same when set to "headphones".

Sounds like one of our 496's isn't working like it's supposed to. I'm going to play with this some more, and try another audio device as an input to the intercom. If I'm still having problems by Monday, I'll try to give Garmin a call.

Thanks,
Rusty

Here's a little more info for anyone who's playing along. Today, I pulled my 496 out of the plane, and plugged it in place of my friend's 396 in his plane. He has the same PMA4000 intercom, and has his L and R channels tied directly together just like mine. The 496 had the same static like distortion in his plane.

I have also run my 496 directly into the stereo input of the Lightspeed thirty 3G headsets, and it's fine. I've run a walkman type stereo into my intercom music input (L and R still tied together), and that was fine too.

The conclusion I came to was that the PS Engineering folks were probably right when they said some devices just don't like having their channels tied directly together. FWIW, I talked to Garmin too, and they didn't have anything better to offer.

I did some searching on stereo to mono adapters, and it seems that the more proper way to connect them is with some resistors. If I come up with a fix, I'll post it here.

Cheers,
Rusty (7.3 hours)

(Edited to remove details of the changes that didn't end up helping)

496 Audio Page

Dear Rusty:

You will want to locate the audio page in the GPS496 that allows you to select either line out or intercom out. Select Intercom out.

Apparantly the engineers at GARMIN made feature selectable now and I am under the impression that the line out level is less desireable.

Hope this helps.

Mark Scheuer
PS Engineering, Inc.
www.ps-engineering.com

Hi Mark,

Best I can tell, there is absolutely no difference between "line out" and "headphones" on my unit. I'm wondering if it's possible they didn't quite have this working correctly when I bought my early 496?

Walt did have better luck with "headphones", and that's what I would have guessed to use for a dedicated music input. The default setting is "line out", which is supposed to be a better setting for a normal audio panel input. Originally, I had the 496 inputing into NAV1 on the intercom, but the volume was too low to hear. That might be another clue that my "line out" isn't what it should be for a standard audio panel input.

Right now, I have a one end of two 10k resistor on the left and right channels, with the other end of each resister tied together. The junction of the resistors is the mono input to the intercom. This is still going to be too low in volume I believe, so I'll likely reduce the resistor size as a next attempt. I've got a few other tests in mind as well.

Thanks,
Rusty

more info

I did some further tests, and found that I can run either the left, or right channels of the 496 into the music input, and everything is fine. There's plenty of volume, and no noise problems when I do that. When I try to connect both channels, the noise appears.

Is anyone else running their 496 audio into a mono music input with both channels tied together? I don't know if this is a problem with my particular 496, or if this happens with all of them.

Thanks,
Rusty