Are standard black Motorola microphones all identical

g8tzl2004 · Post by **g8tzl2004** » Mon Mar 06, 2006 8:03 am

I have always assumed that the standard black Motorola microphone which is used on the GM300 , GM350 , GM950 , GM340 etc are identical.

They certainly look identical.

I have recently acquired a GM950 and also have a GM300 and GM350.

When I was setting up the GM950 , I used my GM300 mic rather than the actual mic that came with the radio (which looked identical).

The model number of the GM300 mic is HMN3596A while the model number of the GM950 mic is GMN6146C.

Using the "GM300" mic with the GM950 , the mic gain was a little low. There is an option in software to increase mic gain . Originally it was set to zero - so I increased it to the next incremental level which was 11dB - at this level , the mic audio was just right and sounded very nice .

I then decided to check the actual GM950 mic and found that the mic gain was far too high - I had to hold the mic around 1 foot away!! I guess if the mic gain setting was still set to zero (rather than 11dB) , then the original GM950 mic would probably have sounded OK.

My conclusion is that the GM950 mic (GMN6146C) has a higher gain preamp installed compared to the GM300 mic. OR my GM950 mic is faulty. I have a few GM300 mics (HMN3596A) and they all sound identical.

Any thoughts?

Cheers

Will · Post by **Will** » Mon Mar 06, 2006 1:17 pm

Since the mid 60's the output of the mobile mic has been the same.
Even the older Motrac mics from the 60's work on Maxtrac, Radius, Syntor and Spectras with the approate cable/wiring.

The Maxtrac, Radius mobile mics work on SyntorX9 and Spectra with the correct cable/wiring.

I have a couple of mics that look like the Jedi speaker mic with three added buttons with a coil cord and 8 pin modular plug. They work on Maxtrac/Radius mobiles but sound garbled or bassy, so maybe /\/\ is changing the mic electrical output specs after all these years.....

Post by **wavetar** » Mon Mar 06, 2006 1:56 pm

Will wrote: I have a couple of mics that look like the Jedi speaker mic with three added buttons with a coil cord and 8 pin modular plug. They work on Maxtrac/Radius mobiles but sound garbled or bassy, so maybe /\/\ is changing the mic electrical output specs after all these years.....

Those are part# GMN6147, I assume? If so, it's for the MCS2000, and will only work properly on that model. They are noise reducing mics & require you to speak at least 12 inches away so they don't sound distorted.

Todd

wa2zdy · Post by **wa2zdy** » Tue Mar 07, 2006 5:06 am

Most of the Ma M mics still around for mobile radios are decendants of the carbon mics they used 50 years ago. (GE did the same thing; my Pre-Prog base had a carbon mic.) Ma M converted over to the mics with solid state amps in the late 50s and early 60s and they used the bias voltage that had been on the mic audio line for the carbon mics.

They still use the same setup today for the most part and as such a mic made today will indeed work on the Motrac and even older stuff.