An audio pre-amp for wired headset use with the Motorola DM4000 series. by ‘Mot Orious’

This is a very useful article penned by Mot Orious  here at GB7MB – i only posted it  !

The circuit presented below is a simple op-amp based pre-amp to provide the necessary gain to enable a two terminal electret microphone to be used with the rear microphone input on the Motorola DM4000 series transceivers.
The circuit can easily be constructed on a small piece of 0.1″ Veroboard or similar.
For vehicle use the 12V supply is ideally obtained from the switched auxiliary output, maybe tapped off the cigar lighter socket etc. Screened cable should be used between the headset and the input to the pre-amp. The output is taken via screened cable to the rear accessory connector on the DM4000 series transceiver. PTT is also routed to the same accessory connector.


The pin-out of the DM4000 series accessory connector is shown below. This is the view looking towards the back of the set, pin 2 is top left, pin 25 bottom right.




by ‘Mot Orious

 All work, text and images © GB7MB

A USB programming lead for the Motorola DM4000 series of mobile transceivers. by ‘Mot Orious’

This is another very useful article penned by Mr. Mot Orious  here at GB7MB – i only posted it.

The USB programming lead for the DM4000 series is an expensive item if bought from Motorola. However construction of a home made version is not complex.

You will need

1. An old, good quality USB lead
2. An accessory plug, Moto part No. PMLN5072A.
3. Ideally a crimp tool to suite, however a soldering iron and needle nose pliers will suffice.

Cut the USB cable to the required length removing the socket end. Remove approximately 35mm of outer jacket from the cable taking care not to damage any inner insulation or the bare earth wire within the cable.

USB cables normally have the following standard colour code
D+       =     Green
D-        =     White
+5V      =    Red
Gnd     =    Black

Check yours just to be sure !


Note the bare (shield) wire is also crimped together with the ground wire.

A note about pin insertion. The pins used in the accessory connector must be inserted with the correct orientation. As can be seen from the image below, the pins have a locking protrusion. The pins are inserted so the protrusion is pointing down for the bottom row and pointing up for the top row. This ensures the pins lock into the shell and enables the pin removal tool to function correctly. The pin removal tool is inserted into the lower or upper slot adjacent to the respective connection pin.



By  Mot Orious
 All work, text and images © GB7MB
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