V

vic syracuse

Well Known Member
So, I doscovered something interesting on the trip to SNF. Idle hands during boring cruise. I failed the PMA 8000BT audio panel to see if I still had com 1 audio on the pilot's headset. Guys what? No audio. It would transmit as I could see the TX on the Avidyne 540. When I got home I verified I had carrier with modulation, but still no audio. After trying to understand how it could work through the Audio Panel and not in bypass mode and coming up with no good scenario, I tore into the wiring. 3 hours later after making up harnesses and verifying wiring for the umpteenth time I tried the mono stereo switch on the Bose headset. Guess what? It was in mono and not stereo. I am of the opinion that it shouldn't matter, but it does and I could duplicate it. No audio if in mono, but OK if in stereo. I tried my Lightspeed Zulu's and they work in BOTH mono and stereo.
It must be an impedance mismatch between the Avidyne 540 and the BOSE A20's when in mono mode.
I am glad I discovered it, as I routinely move the headsets between the 10 and the Kitfox, and the kitfox is mono while the 10 is stereo.

The guys at PS Engineering weren't aware either. I will follow up with them now that I've solved it.

Vic
 
Vic,
In fail safe mode, headsets in stereo, which ear do you hear the radio in? It should be left. If it's the right, you have the left and right channels reversed. If they're reversed, then fail safe operation in mono depends on whether the headset parallels left and right, or just uses left (tip). To confirm this use the Bose in mono, fail safe (audio panel off); pull the plug out one click (about 1/4") and see if it now works.
For there to be no audio due to an impedance mis-match seems unlikely.

Bob
 
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I suspect Bob has nailed it---------this was what I figured the issue was as I read your post.
 
Fail safe mode

vic syracuse said:
I checked that it was wired correctly, but reversing them will probably work. I will try it.

Vic
Click to expand...

For the pilot's headset to hear com 1 when power is removed from the audio panel, the LEFT channel must be wired to the tip of the headphone jack, when using a mono headset.
 
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