Audio Help Needed

[todehnal]

I have the older Skyview conversion harness installation. Both the pilot, and copilot mic jacks are isolated according to the plans. My headphone jacks are not. They are grounded via the mounting, without the isolator washers. In an effort to reduce interference, and while chatting with the intercom guys at Oshkosh, it was suggested that I isolate the headphone jack from the airframe, like the mic. Apparently, not using isolation washers is quite unusual in the intercom world.

As a layman, I am not sure what to do.
First, is this going to help any with noise, or should I just leave it alone??
Next, Can I just open up the hole and install the isolation washers on the headphone jacks? These washers were included in my kit!
Do I need an additional ground wire on these jacks, now that they don't have chassis ground, and If I do, do I need shielded wire, and where would they go?

Hope someone can help. This is about 3 notches above my pay-grade, and I would like to stay out of trouble here.

Thanks. Tom

[BobTurner]

Yes isolate the jacks.
Yes you need a ground wire.
Run all wires using multiconductor shielded cable, connect shield to ground only at the avionics end. It should mimic your mike wiring.

[todehnal]

Thanks Bob,
I guess I will need to run a shielded wire through the tunnel, and up to the avionics bay. I was afraid that was going to be the case. It sure would have been nice if I would have had that info when installing the tunnel harness. Oh well!! Tom

[N804RV]

Actually, grounding the headphone audio via the barrel (no isolation washer), but grounding the mic jack to the audio common (using the isolation washer) is not that unusual. As long as you've followed general practices in grounding audio circuits, I wouldn't think this should cause any problems at all.

The only caveat would be that I would follow the installation instructions provided by the intercom manufacturer.


However, if you want to try a different ground point for headset audio, its a simple matter to unscrew the hex nut, pull the audio jack out of the panel and run a temporary ground wire to an appropriate ground stud, and then isolate the jack and plug with some cardboard or such. Maybe you could tape it to something temporarily. Then, try a "test-flight". Just starting the engine and turning the normal avionics on should do it. I'd try it one audio jack at a time with a couple of known good headsets and someone to man the other headset.

Check out the Sigtronics SPA-4SI 4 place stereo intercom wiring diagram. Notice the difference between grounding for the mic jack and the audio jack. The instructions even say to make a 3/8" hole for the audio jack, but a 1/2" hole for the mic jack. The larger hole is so the mic jack barrel will not contact the airframe.

[Gagarin737]

I also have the old harness and the jacks are not isolated. The fuel pump and the strobes have the suppression filter/capacitors. Sound quality is better than expected.

[N804RV]

Originally Posted by N804RV

The only caveat would be that I would follow the installation instructions provided by the intercom manufacturer.

Just to clarify: There is more than one way to skin the audio ground cat. Sigtronics uses one way. Here another way: PS Engineering PM1200 intercomm

Either work just fine and both are installed in many, many GA airplanes. So, the answer is, given the equipment you have, what do the installation instructions say?

[Mich48041]

Most RV-12s are wired according to Van's plans and the headphone audio works just fine. But it will not hurt anything to isolate the headphone jacks during the build while it is easy to do.
Joe Gores

[todehnal]

Thanks for everyone's thoughts, and ideas. I am wired according to Van's plans. By the way, grounding the headset via the barrel to the airframe is also supported in the intercom installation manual. I had terrible noise when I first hooked it up. I was able to eliminate much of it by adjusting the side tone levels. I still had a little, but it was more prominent with my David Clark headset, than any other. In an effort to totally eliminate the issue, I contacted Van's. The first suggestion was to eliminate the music input. To be honest, that worked quite well, and satisfied my need. Later, I received additional ideas from Van's via email. One of the approaches in this document was to isolate the headset ground, but didn't give details. Apparently this will become the practice in later kits. I thought that I would try that, and see if it resolved my music input issue. But, for now, I plan to leave the music input disconnected, and fly the airplane, at least until my first condition inspection.

[D&M Dan]

I really need help trying to figure out this issue. I have looked through all the threads but don't see the answer.
First off I have the Skyview conversion harness with the SL40 and Flightcom 403. My finish kit was shipped prior to 08/2011. The problem is very faint muffled audio in the headsets. This includes intercom, radio transmissions in and skyview audio.
I have tried 3 different headsets alone and together. I have removed both phone and mic jacks from the floor to eliminate the grounding issue there. I have tried changing settings in the Garmin with no improvement. However I am able to transmit to a handheld radio loud and clear.
I have also tried to pin out each wire from the jacks but I am not finding them at the AV 5000. Not clear which harness I should be checking in. The wiring drawing shows for instance GR/Wh to pin 13 but which harness for pin 13?
Any suggestions would be greatly appreciated.
Thanks

[Raymo]

If working inside a hangar, some lights will cause lots of static. Turn them off and see if things improve.