headset impedance differences
mark meehan
want back. Both have the standard single military type plug on the chord.
Does anyone know if there is an easy way to convert these for use in a GA
aircraft with 2 plugs on the chord? I believe the impedance of the mil
headset is different than normal GA headsets. These headsets also have
dynamic mics so I don't know how much of a difference that makes. Also, the
patch chord available from Sportys does not work. Thanks in advance.
mark
k gallimore
I have used GA and military headsets interchangeably for years. The
microphone has a "nominal" impedance of 150 ohms and the earphones have
a "nominal" 8 ohm inpedance. I made an adapter to use my cheap Telex
in helos. Works fine. Can't tell you more without knowing what type of
plug you have. A few minutes work with an Ohmmeter will tell you what
you need to know.
Kevin Gallimore
Jim Weir
shared these priceless pearls of wisdom:
->Mark-
->
-> I have used GA and military headsets interchangeably for years.
No offense, perhaps you could enlighten the rest of us who have been struggling
with this problem for 30 years or so your secret. It certainly isn't obvious to
the casual observer.
->The microphone has a "nominal" impedance of 150 ohms
and is dynamic, with an output measured in tens of millivolts, while a civilian
microphone is amplified to resemble a carbon microphone with an output measured
in hundreds to thousands of millivolts (half a volt to a volt or so, pp).
and the earphones have
->a "nominal" 8 ohm inpedance.
While a civilian headset uses an "inpedance" of not less than 150 ohms. How do
you make the conversion?
I made an adapter to use my cheap Telex
->in helos. Works fine. Can't tell you more without knowing what type of
->plug you have.
The plug style makes not a whit of difference until you address the
level/impedance problems above.
A few minutes work with an Ohmmeter will tell you what
->you need to know.
But not what you need to do.
Jim
Jim Weir (A&P, CFI, and other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com j...@rst-engr.com
surfer
ask him for it, because there is a bit more to it than just ohm-metering..
(Thanks again, Jim!)
But by the way, when will we get *your* schematic? My KP mag subscription runs out.
F5RQH, Johan (Also has loads of mil headsets lying around)
Btw, Jim: they work fine on my FT-7B, though...
Jim Weir wrote:
<<sssnipp!>>
k gallimore
Apparently my problem is my ignorance of GA ICS stations. In the
military world, the microphone feeds
a preamp in the ICS head; any bias for an electret is supplied from the
ICS. The ICS crew station
output (the amplified mic signal) feeds a 150 ohm bridging resistor
common to all the stations (this resistor usually comprises the "Audio
Junction Unit"or AJU). The signal level at the AJU is about 1V. peak to
peak. The output to drive the earphones comes from a complementary
symmetry pair having a very low output impedance.
In short, GA headsets have no problem with military intercoms; I've
used Telex, DC, and even the Telex ANR
sets with no problem. My error was in thinking this would work both
ways. If someone wants to post a
schematic of a GA intercom, I'll try to come up with an adapter box to
make up for misleading the group.
No warranty express or implied.
Kevin Gallimore
Joe Della Barba
wrote:
>Mark-
>
> I have used GA and military headsets interchangeably for years. The
>microphone has a "nominal" impedance of 150 ohms and the earphones have
>a "nominal" 8 ohm inpedance. I made an adapter to use my cheap Telex
>in helos. Works fine. Can't tell you more without knowing what type of
>plug you have. A few minutes work with an Ohmmeter will tell you what
>you need to know.
>
>Kevin Gallimore
>
>mark meehan wrote:
>>
>> I just got out of the military and find myself with 2 headsets they did not
>> want back. Both have the standard single military type plug on the chord.
>> Does anyone know if there is an easy way to convert these for use in a GA
>> aircraft with 2 plugs on the chord? I believe the impedance of the mil
>> headset is different than normal GA headsets. These headsets also have
>> dynamic mics so I don't know how much of a difference that makes. Also, the
>> patch chord available from Sportys does not work. Thanks in advance.
>>
>> mark
An ohmeter will tell you NOTHING about impedance at all! Impedance is
measured with AC.
If you use headphones of too low impedance they may overload the radio
audio out and will "hog" all the power from the other headsets. A
cheap radio shack audio transformer will take care of the headphone
end of it.