Headset conversion

[aol]

I have a couple of Davd Clarks given to me by my nephew, a former Air Force
loadmaster. I want to convert to use on civil aviation radios. As a former
engineer and ham radio operator I understand radio principles very well and
I am aware of the impedances of military com systems (5 ohm mics, 19 ohm
speaker). I am not that savy with civil aviation radios, however. I have
managed to easily convert the speaker side with impedance matching
transformer. I am also aware that the mic side is not just a simple
impedance matching issue. Does david clark have a mic element replacement
for the M87A/C boom mic that I can order without having to order a complete
conversion kit (for over $100 dollars). I know I would be just as well off
to get a headset off ebay but I want to waste my time with this useless
project for those rainy days when I can't fly the plane.
Cheers all
Bruce Stafford (KE5NT)

[Gord Beaman]

"RST Engineering" > wrote:
--cut--
>> for the M87A/C boom mic that I can order without having to order a
>> complete conversion kit (for over $100 dollars).
>
>Translation: I don't want to call Clark myself because they might ask some
>embarassing questions about the headset's ancestry. Will any of you admit
>to similar circumstances and tell me how you got around the system?
>
>Jim

Jealous because you have no service time james?

--

-Gord.
(use gordon in email)

[RST Engineering]

Why would I be jealous of not having service time? I certainly respect
those who chose to perform that duty, but I think I saved more lives with my
defense electronic designs than I would have flying a desk and steering it
with a coffee cup.

It simply ****es me off when somebody is so stupid as to admit how he came
by what appear to be purloined goods paid for with my tax money. He could
have said that he got them surplus, or found them on ebay, but he had to
give us the shadowy channel by which they came his way.

Jim


>
> Jealous because you have no service time james?
>
> --
>
> -Gord.
> (use gordon in email)

[Brian Whatcott]

On Sat, 19 Feb 2005 08:58:50 -0600, "aol" > wrote:

>I have a couple of Davd Clarks given to me by my nephew, a former Air Force
>loadmaster. I want to convert to use on civil aviation radios. As a former
>engineer and ham radio operator I understand radio principles very well and
>I am aware of the impedances of military com systems (5 ohm mics, 19 ohm
>speaker). I am not that savy with civil aviation radios, however. I have
>managed to easily convert the speaker side with impedance matching
>transformer. I am also aware that the mic side is not just a simple
>impedance matching issue. Does david clark have a mic element replacement
>for the M87A/C boom mic that I can order without having to order a complete
>conversion kit (for over $100 dollars). I know I would be just as well off
>to get a headset off ebay but I want to waste my time with this useless
>project for those rainy days when I can't fly the plane.
>Cheers all
>Bruce Stafford (KE5NT)
>
[I compacted the following from an "Avionics" article]

" There are applicable standards for cockpit audio, namely TSO-C50,
and DO-214 for signal guidelines.

Once upon a time, a microphone was a carbon element, with a 150-ohm
impedance (borrowed from the telephone industry). It required external
DC excitation of at least 8 to 12 volts DC to produce audio of about
150 millivolts (mV). Headsets and radio outputs had a 600-ohm
impedance and required at least 50 milliwatts (mW) of power to produce
acceptable levels. Both microphone and headset signals were normally
referenced to the airframe ground. If a speaker existed, it was
understood to have an impedance of 4 ohms and be driven at 5 watts.

Military operators adopted "noise canceling" microphones like the M87
and M101, which had a dynamic microphone (mic) element built like a
studio microphone. The M87 had an active diaphragm with balanced
openings on both sides of the mic housing. The concept has the voice,
mixed with ambient noise, entering one side of the diaphragm and
noise-only entering the other side. The noise cancels mechanically in
the diaphragm, and the resulting signal is voice only.

Dynamic self-excited microphones offered low impedance (about 5 to 8
ohms) but operated at low signal level (often under 1 mV).
A low-level microphone must be accompanied by a low-impedance headset
to keep drive voltages low. This established the 8- to 20-ohm standard
headset/dynamic microphone combination commonly used by the military.

.. Military users also adopted amplified dynamic microphones and
600-ohm headsets as an alternative. (The amplified dynamic mic has low
impedance but also a small outboard amplifier to make it work like a
"carbon equivalent" microphone.)
Military audio systems often had to support different mic and headset
standards within a single station (or audio box for each pilot). And
each user typically had his own station control within the aircraft."

Hope this helps

Brian Whatcott Altus OK

[Brian Whatcott]

On Sat, 19 Feb 2005 08:38:07 -0800, "RST Engineering"
> wrote:

>I hate to be so negative on a first time poster, but this one needs some
>examination ...
>
>
>"aol" > wrote in message news:auIRd.24464$Cs.3230@okepread02...
>
>>I have a couple of Davd Clarks given to me by my nephew, a former Air Force
>>loadmaster. I want to convert to use on civil aviation radios.
>
>Translation: All of our tax dollars went to pay for some Air Force issue
>headsets that my nephew bagged while he was on active duty and I want you
>all to be an accessory to the crime by telling me how to modify them. I
>have just admitted to a possible felony by my nephew and a possible felony
>by me in keeping what I suspect to be stolen property.
>
>
> Does david clark have a mic element replacement
>> for the M87A/C boom mic that I can order without having to order a
>> complete conversion kit (for over $100 dollars).
>
>Translation: I don't want to call Clark myself because they might ask some
>embarassing questions about the headset's ancestry. Will any of you admit
>to similar circumstances and tell me how you got around the system?
>
>Jim
>

Jim is possibly going a little hard on this poster. When I left the
Air force, all my kit went for disposal/destruction. Gear in general
is not recycled.

Brian Whatcott Altus OK

[Gord Beaman]

Brian Whatcott > wrote:
--cut--
>
>Jim is possibly going a little hard on this poster. When I left the
>Air force, all my kit went for disposal/destruction. Gear in general
>is not recycled.
>
>Brian Whatcott Altus OK

Yes that's true...especially personal gear like headsets and boom
mikes...the boom mike require close contact with the mouth and
the headphones and headband are equally 'close to the person' and
are discarded when no longer needed by that person. Jim is not
known for his courteous handling of people I've seen.
--

-Gord.
(use gordon in email)

[Jon A.]

Don't worry about what this guy says, he bends situations to
accommodate himself.

Go ahead and call Clark and ask for what you need. If you have a set
that was originally sold to the government then they'll need to sell a
replacement to them, so they'll be happy. But, you might find that it
would be cheaper to get a used set on Ebay.

The other alternative is to send them off to PS Engineering for a
makeover. Again, an expensive proposition.


On Sat, 19 Feb 2005 08:38:07 -0800, "RST Engineering"
> wrote:

>I hate to be so negative on a first time poster, but this one needs some
>examination ...
>
>
>"aol" > wrote in message news:auIRd.24464$Cs.3230@okepread02...
>
>>I have a couple of Davd Clarks given to me by my nephew, a former Air Force
>>loadmaster. I want to convert to use on civil aviation radios.
>
>Translation: All of our tax dollars went to pay for some Air Force issue
>headsets that my nephew bagged while he was on active duty and I want you
>all to be an accessory to the crime by telling me how to modify them. I
>have just admitted to a possible felony by my nephew and a possible felony
>by me in keeping what I suspect to be stolen property.
>
>
> Does david clark have a mic element replacement
>> for the M87A/C boom mic that I can order without having to order a
>> complete conversion kit (for over $100 dollars).
>
>Translation: I don't want to call Clark myself because they might ask some
>embarassing questions about the headset's ancestry. Will any of you admit
>to similar circumstances and tell me how you got around the system?
>
>Jim
>

[aol]

For the RST guy with the hard on - I asked J about the origin of the
headsets and he said he was asked to take them with him when he left the
service. He had used them for a number of years. So much for that. By the
way, I am a purple heart Vietnam veteran of the Marine Corps and not much
into stealing government property. The last poster is thanked immensely for
the good info. I have an idea I'm working on which I think will work but
since you have a least one dip**** on this forum I don't think I'll be back.
I've got better things to do than get ****ed of at "patriots."

"Brian Whatcott" > wrote in message
...
> On Sat, 19 Feb 2005 08:58:50 -0600, "aol" > wrote:
>[i]
>>I have a couple of Davd Clarks given to me by my nephew, a former Air
>>Force
>>loadmaster. I want to convert to use on civil aviation radios. As a former
>>engineer and ham radio operator I understand radio principles very well
>>and
>>I am aware of the impedances of military com systems (5 ohm mics, 19 ohm
>>speaker). I am not that savy with civil aviation radios, however. I have
>>managed to easily convert the speaker side with impedance matching
>>transformer. I am also aware that the mic side is not just a simple
>>impedance matching issue. Does david clark have a mic element replacement
>>for the M87A/C boom mic that I can order without having to order a
>>complete
>>conversion kit (for over $100 dollars). I know I would be just as well off
>>to get a headset off ebay but I want to waste my time with this useless
>>project for those rainy days when I can't fly the plane.
>>Cheers all
>>Bruce Stafford (KE5NT)
>>
>
>
> " There are applicable standards for cockpit audio, namely TSO-C50,
> and DO-214 for signal guidelines.
>
> Once upon a time, a microphone was a carbon element, with a 150-ohm
> impedance (borrowed from the telephone industry). It required external
> DC excitation of at least 8 to 12 volts DC to produce audio of about
> 150 millivolts (mV). Headsets and radio outputs had a 600-ohm
> impedance and required at least 50 milliwatts (mW) of power to produce
> acceptable levels. Both microphone and headset signals were normally
> referenced to the airframe ground. If a speaker existed, it was
> understood to have an impedance of 4 ohms and be driven at 5 watts.
>
> Military operators adopted "noise canceling" microphones like the M87
> and M101, which had a dynamic microphone (mic) element built like a
> studio microphone. The M87 had an active diaphragm with balanced
> openings on both sides of the mic housing. The concept has the voice,
> mixed with ambient noise, entering one side of the diaphragm and
> noise-only entering the other side. The noise cancels mechanically in
> the diaphragm, and the resulting signal is voice only.
>
> Dynamic self-excited microphones offered low impedance (about 5 to 8
> ohms) but operated at low signal level (often under 1 mV).
> A low-level microphone must be accompanied by a low-impedance headset
> to keep drive voltages low. This established the 8- to 20-ohm standard
> headset/dynamic microphone combination commonly used by the military.
>
> . Military users also adopted amplified dynamic microphones and
> 600-ohm headsets as an alternative. (The amplified dynamic mic has low
> impedance but also a small outboard amplifier to make it work like a
> "carbon equivalent" microphone.)
> Military audio systems often had to support different mic and headset
> standards within a single station (or audio box for each pilot). And
> each user typically had his own station control within the aircraft."
>
> Hope this helps
>
> Brian Whatcott Altus OK

[RST Engineering]

My apologies, sir, if I misstated the case.

I currently live within spitting distance of three Air Force bases, and
formerly within baseball throwing distance of three Navy bases and two
Marine Corps bases. I have been doing "do it yourself" avionics for over 35
years. The number of times I've been asked at a local meeting how to
convert "this helmet I just picked up out of the trash" number in the
dozens, if not the hundreds. I just don't believe that the military is
throwing away that much hardware, especially as some of the stuff I've seen
as "trash" has never been worn.

So if I lumped you in with all those goofballs, again, my apologies. To
make amends, tell you what I'm going to do. I'll email you my original
design for conversion of your headset if you will confirm receiving this
message. Can you receive attachments, and can you read .pdf files?

Jim


"aol" > wrote in message news:1j8Sd.27608$Cs.7792@okepread02...
> For the RST guy with the hard on - I asked J about the origin of the
> headsets and he said he was asked to take them with him when he left the
> service. He had used them for a number of years. So much for that. By the
> way, I am a purple heart Vietnam veteran of the Marine Corps and not much
> into stealing government property. The last poster is thanked immensely
> for the good info. I have an idea I'm working on which I think will work
> but since you have a least one dip**** on this forum I don't think I'll be
> back. I've got better things to do than get ****ed of at "patriots."

[Mike W.]

My brother is currently in the Navy, beleive me the military is very
wasteful. He has brought home some things that were new (clothing mostly)
and he was told by superiors to 'make it go away, it's getting trashed'.

"RST Engineering" > wrote in message
...
> My apologies, sir, if I misstated the case.
>
> I currently live within spitting distance of three Air Force bases, and
> formerly within baseball throwing distance of three Navy bases and two
> Marine Corps bases. I have been doing "do it yourself" avionics for over
35
> years. The number of times I've been asked at a local meeting how to
> convert "this helmet I just picked up out of the trash" number in the
> dozens, if not the hundreds. I just don't believe that the military is
> throwing away that much hardware, especially as some of the stuff I've
seen
> as "trash" has never been worn.
>
> So if I lumped you in with all those goofballs, again, my apologies. To
> make amends, tell you what I'm going to do. I'll email you my original
> design for conversion of your headset if you will confirm receiving this
> message. Can you receive attachments, and can you read .pdf files?
>
> Jim
>