Wiring Headset Jacks

[hamer]

Is there any reason (or regulation) that people typically use a two conductor and three conductor shielded wire for the headset jacks rather than using a single 5 conductor shielded wire? The shields all terminate together, but I guess having all 5 conductors twisted together might not be ideal?

Thanks for the input.

 

[Dana]

Backwards compatibility with existing avionics. Some newer headsets, like those from Lynx and Comtronics, have a single cord/plug, but require an adapter to connect to existing standard radios. Such things are popular for ultralights and experimentals.

The standare two plug setup dates back to telephone switchboard hardware of the 1930s, using components that were readily available back then.

 

[bnt83]

For one thing 5 conductor shielded wire at a reasonable cost doesn’t exist, at least not in 24 gauge.

Second,if you have crosstalk/noise using a 5 conductor shielded cable have fun rewiring it

Third, with typical intercoms every seat doesn't have a phone wire that runs all the way back to the audio panel. In fact, typically all passenger phone jacks are wired in series. Pilot and copilot phones are wired in parallel

 

[asicer]

For one thing 5 conductor shielded wire at a reasonable cost doesn’t exist.

Second,if you have crosstalk/noise using a 5 conductor shielded cable have fun rewiring it

Third, with typical intercoms every seat doesn't have a phone wire that runs all the way back to the audio panel. In fact, typically all passenger phone jacks are wired in series. Pilot and copilot phones are wired in parallel

Not sure I understand you correctly. Electrically speaking, it's not obvious to me how jacks wired in series would work or how a parallel circuit could be isolated. Do you really mean to say that pax are wired daisy-chain while pilot/copilot are wired home-run?

 

[bnt83]

Not sure I understand you correctly. Electrically speaking, it's not obvious to me how jacks wired in series would work or how a parallel circuit could be isolated. Do you really mean to say that pax are wired daisy-chain while pilot/copilot are wired home-run?

Correct

 

[asicer]

Correct

View attachment 73085

Ah, yep. That's daisy chain and home run alright.

 

[AK737pilot]

I seem to remember reading somewhere that the audio wires and mic wires shouldn’t be in the same shield to prevent introducing noise....

Yep, just looked it up, PS Engineering says “Don’t EVER run mic and headphone audio in the same shield (it will squeal!).


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[hamer]

The radio I'm looking to hook up has discrete Pilot/Copilot, so I'll be running two sets of wires.

I seem to remember reading somewhere that the audio wires and mic wires shouldn’t be in the same shield to prevent introducing noise....

Yep, just looked it up, PS Engineering says “Don’t EVER run mic and headphone audio in the same shield (it will squeal!).


Sent from my iPhone using Tapatalk

Thanks guys. This is reason enough for me.

 

[Rob58]

I have also read that the cable shields for the audio circuits should be isolated from the airframe ground... any opinion on this?

 

[Dan Thomas]

In fact, typically all passenger phone jacks are wired in series. Pilot and copilot phones are wired in parallel

That diagram shows the pax phones and mics all wired in parallel.

 

[Dan Thomas]

I have also read that the cable shields for the audio circuits should be isolated from the airframe ground... any opinion on this?

They should be grounded at the audio panel end, and ungrounded at the jacks. The jacks themselves should be mounted with insulating washers. If they're grounded, or if the shields are grounded at both ends, airframe currents run through them and can cause noise in the headsets.

Antenna shielding is grounded at both ends.

 

[Rob58]

They should be grounded at the audio panel end, and ungrounded at the jacks. The jacks themselves should be mounted with insulating washers. If they're grounded, or if the shields are grounded at both ends, airframe currents run through them and can cause noise in the headsets.
Antenna shielding is grounded at both ends.

Makes perfect sense... thanks for the explanation!