Microphone impedance conversion...help me Jim Weir!

I need to know how to make a headset converter that allows me to use my
military (low impedance mic, single plug) headset in a GA airplane. The
plug pinouts I can probably figure out, but the mic impedance matching has
me stumped. Thanks all.

-Scott

I'm getting ready to write a faq on this one, we answer it so often.

OK, here we go. It is not a simple impedance matching problem. It is more
like "how do I get my barbecue to paint the house" issue. The military
microphone is generally moving coil (dynamic) that puts out a few millivolts
at an impedance of somewhere between 20 and 50 ohms.

The civilian microphone uses several technologies (dynamic, electret, ribbon
....) to transduce the voice to an electrical signal, but whatever technology
is used it is always followed by an amplifier of some sort to force the
output to resemble a carbon granule microphone which "looks" like somewhere
in the vicinity of 600 ohms with an output of half a volt or so.

Somewhere in these groups a couple of months ago, there was a pointer to an
Aussie site with a single transistor very simple amplifier that was reported
to do the conversion well. I lost that pointer; can somebody else repost
that site please?

Jim


"Scott VanHoveln" wrote in message
...
I need to know how to make a headset converter that allows me to use my
military (low impedance mic, single plug) headset in a GA airplane. The
plug pinouts I can probably figure out, but the mic impedance matching has
me stumped. Thanks all.

-Scott

"Scott VanHoveln" wrote in message
...
I need to know how to make a headset converter that allows me to use my
military (low impedance mic, single plug) headset in a GA airplane. The
plug pinouts I can probably figure out, but the mic impedance matching has
me stumped.

Jim will give a more useable answer,
but here goes for what it's worth:

There's more issues than impedance.
Standard airborne equipment is still ridicilously
designed for the carbon microphone of the 1930's or so,
it feeds a DC bias into the microphone jack
which is unhealthy to dynamic mike cells.

Do you know how your headset mike works?
If it is dynamic, some kind of adapter will be required.
If it is (as I suppose, because that's state of the art)
a condenser type with the required preamp,
it has a fair chance of needing only an adapter plug.

Just on a theoretic sidenote:
if impedance matching is the real issue,
a transformer is the answer.

Good luck!

"RST Engineering" wrote in message
...
I'm getting ready to write a faq on this one, we answer it so often.

Somewhere in these groups a couple of months ago, there was a pointer to
an Aussie site with a single transistor very simple amplifier that was
reported to do the conversion well. I lost that pointer; can somebody
else repost that site please?

Jim


I think this is the site.
http://www.gfa.org.au/vic/mgc/micamp.htm

John Severyn
@KLVK

Thatzit. Thanks.

Jim


"J. Severyn" wrote in message
. ..



I think this is the site.
http://www.gfa.org.au/vic/mgc/micamp.htm

John Severyn
@KLVK

What about impedance matching for the phones? I've been told they're
different too..
Thanks

"karel" wrote in message
...

"Scott VanHoveln" wrote in message
...
I need to know how to make a headset converter that allows me to use my
military (low impedance mic, single plug) headset in a GA airplane. The
plug pinouts I can probably figure out, but the mic impedance matching has
me stumped.

Jim will give a more useable answer,
but here goes for what it's worth:

There's more issues than impedance.
Standard airborne equipment is still ridicilously
designed for the carbon microphone of the 1930's or so,
it feeds a DC bias into the microphone jack
which is unhealthy to dynamic mike cells.

Do you know how your headset mike works?
If it is dynamic, some kind of adapter will be required.
If it is (as I suppose, because that's state of the art)
a condenser type with the required preamp,
it has a fair chance of needing only an adapter plug.

Just on a theoretic sidenote:
if impedance matching is the real issue,
a transformer is the answer.

Good luck!

WIth my compliments...

Jim


"Richard Riley" wrote in message
...
On Tue, 28 Nov 2006 10:10:25 -0800, "RST Engineering"
wrote:


It is more
like "how do I get my barbecue to paint the house" issue.

Tomorrow morning I will be shamelessly stealing that line for a
powerpoint presentation.

("RST Engineering" wrote)
It is more like "how do I get my barbecue to paint the house" issue.


With one of these I reckon.

http://www.fantes.com/pastry_brushes.htm
Pastry and Barbecue brushes (scroll down)


Montblack

"RST Engineering" wrote in message
...

"how do I get my barbecue to paint the house"

You put a closed can of paint on the grill, put the grill next to the house,
leave the grill cover opened, and put heat under the can. At some point, the
cover will blow and the paint will splash all over the side of the house.

Move the grill a few feet down and repeat.

Precisely the kind of mickeymouse lashup it takes to convert a military mic
to a ga radio.

Jim



"Steve Foley" wrote in message
news:e3jbh.7700$Kw2.3988@trndny05...
"RST Engineering" wrote in message
...

"how do I get my barbecue to paint the house"

You put a closed can of paint on the grill, put the grill next to the
house, leave the grill cover opened, and put heat under the can. At some
point, the cover will blow and the paint will splash all over the side of
the house.

Move the grill a few feet down and repeat.