Looking for Microphone Impedance Help

[liquidcooled247]

Found this site after searching for over a month all over the internet for a solution to a problem. Its pretty clear there are a bunch of electronics and radio experts here.

So.... Im a police officer that uses a HT750 for work currently. I have an MSA sordin headset which uses a 150ohm dynamic microphone and a PTT from a military MBITR radio. Obviously this is way way too low of impedance to use with the HT750. I cant even find out what the microphone impedance is on the ht750 and ive searched extensively for it.

I know I need a preamp to boost the microphone signal. Without knowing what microphone impedance output I need to have it makes it impossible to figure out a preamp.

Does anybody know how to build a preamp for this setup.

Eventually we are moving to the APX radios so I would like to know if a preamp that works with the ht750 would work with the APX6000 radio when we make the switch.

Im not good at circuit DESIGN but can solder decent and read a diagram/schematic.

Thanks,
Mike

[Jim202]

Found this site after searching for over a month all over the internet for a solution to a problem. Its pretty clear there are a bunch of electronics and radio experts here.

So.... Im a police officer that uses a HT750 for work currently. I have an MSA sordin headset which uses a 150ohm dynamic microphone and a PTT from a military MBITR radio. Obviously this is way way too low of impedance to use with the HT750. I cant even find out what the microphone impedance is on the ht750 and ive searched extensively for it.

I know I need a preamp to boost the microphone signal. Without knowing what microphone impedance output I need to have it makes it impossible to figure out a preamp.

Does anybody know how to build a preamp for this setup.

Eventually we are moving to the APX radios so I would like to know if a preamp that works with the ht750 would work with the APX6000 radio when we make the switch.

Im not good at circuit DESIGN but can solder decent and read a diagram/schematic.

Thanks,
Mike

Is there some reason that your hung up on using the MSA headset?

By the time you get all done trying to cob together some sort of amp to use and your time (cost), you could have put that all that toward finding a better compatible device.

Jim

[liquidcooled247]

^ Its actually a TCI liberator II dual comm setup, its basically a liberator . It is their version of a sordin and uses the same 150 ohm mic, the TCI's have seperate speakers in each earcup. One for ambient audio, and one for radio communications (This may not seem like a big deal, but tactically its huge.) I know they can be preamped and it should not be too difficult to build it. Im not really wanting to waste what is essentially a useless several hundered dollar ptt when a preamp should be able to built cheaply and fairly easily.

Also all ptt's from peltor and MSA are made for low impedance miss, so it would take alot of functionality out of it as I can quick swap with the adapter I built onto any TP-120 connection ptt.

I dont know the impedance for the ht750 microphone and im not the best at electronics design. This is what I'm looking for help with.

[Will]

The Ht 750 and most Motorola portables use a 2000 ohm DC bias for a electret mic, these have a built in amp.

The external mic input audio is about 25 milivolts.

[CircleBat]

your gonna need a 1k impedance mic element..

CircleBat

[abbylind]

I built some similar setups years ago using some military headsets. They had carbon mikes Took the preamp and mike out of an old remote speaker mike and fit the preamp inside one of the headset earpieces. Took some work but its doable. Gotta find power somewhere to power the pre-amp though. IIRC the 750 has + on the asscy jack for the remote speaker mike.
Good luck

[abbylind]

I also took some remote speaker mikes and removed the mike and speaker and routed a military female plug out of the mike housing. The aircraft crewmembers could unplug their headset from the aircraft and plug into this setup. PTT was the same old switch on the remote mike housing.
Worked slick!

[CircleBat]

Use the internal mic element from the motorola P1225 portable.. those sound more clear and will work with the HT750's.. if can't find any, just use a motorola HT600/gp300/.ht750 speaker mic mic element.. If don't have any... PM and i'll send some down

Circlebat