Impedance switch on helmet.

[dapperdan]

Hi,

I recently got a Gentex helmet that has a low impedance Electret mic o (did i get that right?). In my company our helis has different intercom systems for high and low impedance.
I guess i can do this two ways, either i get another mic, a dynamic one, or i can install a switch on the helmet that switches from low to high impedance.
Im looking primarily to get a switch, because this would cause the least hassle when changing aircraft.
Ive searched the forums for similar posts, but what im looking for is a wiring diagram to build this high-low switch.
Has anyone had the same problem, and found a good solution?

Much appreciated,

Dan

[Senior Pilot]

DD,

You may find this post (http://www.pprune.org/6069061-post358.html) to be of some help: the matter has been discussed many times, and it doesn't seem to be a matter of a simple switch.

At least, not that has been answered here!

[9Aplus]

Usefull source here, page 16, nice article "Audio Transformers by Bill Whitlock"

http://www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdf

[dapperdan]

Thanks guys for the input. Ill look into that handbook, im no expert in electronics but ill give it a shot!

[Gomer Pylot]

Some David Clark headset models have the hi-lo switch. They also have a printed circuit card inside, and it's not a matter of a simple switch, you also must have the circuitry. Perhaps DC will sell the circuit card separately, although I've never tried to buy one. DC does have excellent customer service, though, so it's worth a try. I'm also unsure which microphone the switching DC headset uses, but I suspect you'll need to use the same type. A dynamic mike is normally high-impedance, along with most civilian mikes. In the US, only the military normally uses low-impedance electronics, and every civilian aircraft I've been in uses high-impedance.

[MikeNYC]

Dapperdan, you could also use an external impedance converter, which would be more simple than carving up your helmet or swapping mics all the time:

Impedance Converter Single Heli to Single Military - Free Shipping $150 or more! (http://www.pilotshop.com/impedance-converter-single-heli-single-military-p-3740.html)

Drawback is that it's battery powered.

[bigglesbutler]

I quite like the look of the round case option in the link below, scroll down to the first pictures. I too have a Zulu with a low impedance mic and want the ability to jump into a high impedance heli when needed.

http://www.comm-innovations.com/catalog08/Low%20to%20High%20Impedance%20Adapters.pdf

Si

[waragee]

just wondering if there is a simple way to identify which one is which. is it as simple as just not working or a low volume or something like that. for example would it be possible that an R44 that has had other radios and nat boxs fitted somehow have wound up with a low impedence setup instead of a high.
we operate Robinsons and Bell 206's, are we lucky enough that they are common impedance. cheers

[zlocko2002]

life suport gang just atached another mike next to original one on my helmet. i only nead to plug in the one that i nead :-) simple and cheep

[aclark79]

I had a dual impedance switch installed by helicopter helmets.com when they refurbishment my helmet. I like it alot but it does require the right mic/speaker set up. It works just as advertised, lets me switch between our aircraft without changing any mics or having an external converter.

[Pandalet]

I recently went through this, needing to convert my high impedance Zulu to a low impedance aircraft. After going through some people who only pretended to know what they were doing, I eventually ended up with a battery-powered converter box. This works well, in that I can use my headset, but screwed up the vox system in the aircraft, resulting in my mic being permanantly open; ok(ish) if you're flying on your own, but a bit tough on everyone else if you're not.

If you're particularly interested in the specific differences between the technologies, drop me a pm.

[Gomer Pylot]

Why do companies buy aircraft with different impedance avionics systems? It's more expensive in the long run, since two sets of parts have to be kept in inventory, and it's a PITA for all involved. Why not just get the proper avionics in the first place? Here only the military uses low-impedance avionics, and that is purely a matter of inertia, since there are no technical reasons. I've never seen a civilian aircraft with low-impedance avionics, and I'm curious as to why they're in use elsewhere.