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Confused by lemo jack wiring

Raiz

Well Known Member
I plan to fit Lemo jacks as well as the normal GA phone and mic jacks but I've found 3 different wiring diagrams, one from Bose, one from Garmin and one from Vans. They differ in what you do with the shields for the wires between the GA jacks and the lemo jack.

Bose has you connect the shields to audio ground at the GA jacks - image from the Bose install manual.

Garmin has you run the lemo shield wires (and all other wires) all the way back to the the audio panel - image from the GMA 245 manual.

Vans don't have any shields at all on the wires between the GA jacks and the lemo jack - image from the RV-14 wiring diagram.

Does it matter which one I use?
 

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+1 on Stein’s diagram. The goal is to have one, but only one, electrical path for each connection, including grounds. Ground the shield only at the audio panel. Don’t forget to use fiber washers to insulate the jacks from the airframe.
 
I have both and used the Bose schematic. My panel was built by Stein and the GA jacks were prewired. I recommend using a short lead off of your GA jacks, at least for the one connection that has 3 wires connected.

-Marc
 
Ah, the Stein diagram is the same as the Vans one - no shields on the short length of wire between the lemo and GA jacks.
 
What I'd do:
1 ground shields only at audio panel lo
2. bose and aviation jack have separate shield cable from audio panel to plug
3. twisted pair wires to PTT to prevent cross talk into low level analog

All the wire diagrams posted are ambiguous about physical shield connection which is not cool. :)
 
LEMO Jack Wiring

Garmin’s LEMO connector drawing is recommended as the best case for wiring to the GMA audio panels. In the LEMO connector the MIC has its own Lo, but the HS and Power share a return path. The power for the headset returns in the LEMO 2 GND, which is also tied to the headset shields. The best performance for a low noise solution is to always wire back to the audio panel (or source). For the power return (the LEMO 2 GND), we recommend that go back to the audio panel as shown to prevent power return noise from the HS low. For the shields we recommend wiring as shown. For audio carrying wiring, the shield of the wire should be terminated at the audio panel end only.

For cases where a LEMO is being connected to an existing jack, maintaining a shield connection from jack wiring to LEMO wiring (and then back to the audio panel) is important when the distance between jacks is longer than a foot.

For cases where a LEMO is the only jack (diagram shown in Garmin audio panel IM’s), the connections should be run to the audio panel as shown in those diagrams for best performance in regards to reduction of noise.

The Garmin drawing is recommended for best overall performance. Other variations may also work also as each aircraft is different. We’d like to support our drawing if any issues exist, but acknowledge each aircraft may be wired different.

For purposes of keeping grounds at the same point, we recommend running all shields and the LEMO 2 GND back to the GMA or source unit.
Otherwise there is a potential for a difference in grounds from the Headset shields and the GND of the LEMO (and GMA), which would result in noise in the headset speakers.

Thanks,

Justin
 
Video screen capture from Stein

This is a video screen capture from the Stein video explaining Tip, Ring and Shaft.
It clearly says here Do Not Connect shields (at the jacks)

The shielded portion looks like it’s connected only at the audio device (in my case the GMA 245).
 

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This is a video screen capture from the Stein video explaining Tip, Ring and Shaft.
It clearly says here Do Not Connect shields (at the jacks)

The shielded portion looks like it’s connected only at the audio device (in my case the GMA 245).

Looks like they do the wiring in a rough area
 
Garmin’s LEMO connector drawing is recommended as the best case for wiring to the GMA audio panels. In the LEMO connector the MIC has its own Lo, but the HS and Power share a return path. The power for the headset returns in the LEMO 2 GND, which is also tied to the headset shields. The best performance for a low noise solution is to always wire back to the audio panel (or source). For the power return (the LEMO 2 GND), we recommend that go back to the audio panel as shown to prevent power return noise from the HS low. For the shields we recommend wiring as shown. For audio carrying wiring, the shield of the wire should be terminated at the audio panel end only.

For cases where a LEMO is being connected to an existing jack, maintaining a shield connection from jack wiring to LEMO wiring (and then back to the audio panel) is important when the distance between jacks is longer than a foot.

For cases where a LEMO is the only jack (diagram shown in Garmin audio panel IM’s), the connections should be run to the audio panel as shown in those diagrams for best performance in regards to reduction of noise.

The Garmin drawing is recommended for best overall performance. Other variations may also work also as each aircraft is different. We’d like to support our drawing if any issues exist, but acknowledge each aircraft may be wired different.

For purposes of keeping grounds at the same point, we recommend running all shields and the LEMO 2 GND back to the GMA or source unit.
Otherwise there is a potential for a difference in grounds from the Headset shields and the GND of the LEMO (and GMA), which would result in noise in the headset speakers.

Thanks,

Justin

Hi G3X, I am doing the LEMO wiring now with existing GA jacks, and am still confused about the Garmin diagram. It shows the Mic GA wiring with a floating shield at the GA jack, but not shield terminated at the GMA side. Is that intentional, and if so, why is it done that way?
 
I found a discreprency between the Garmin G3X wiring and the SteinAir headset diagram in 2020. I followed the Garmin diagram.

I just installed the LEMO connectors and followed the most recent SteinAir LEMO wiring diagram and everything works great.
 
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