Icom Headset Adapter

Lately I have been doing a bit more contesting. The hand microphone on my Icom 746PRO works well but it is hard to type with a microphone in your hand. I thought about getting a desk microphone and foot pedal but I found the prices for even used desk microphones a bit out of my reach. I moved on to the idea of headsets but the only headset I liked was a Heil. I found it kind of pricey, too.

I started looking for plans to make my own desk microphone or headset, or at least convert something. My Icom manual had a schematic for the HM-36 stock microphone. The drawing showed an electret condenser element, powered with +8VDC. I made a quick search on the internet and I found that I owned several condenser microphones since condenser microphones are commonly used for computers, Xboxes, and other game systems.

I decided on the simplest circuit I could find. The microphone schematic in my manual shows Pin 1 is the audio input, Pin 2 is +8VDC and Pin 7 is the audio ground. I tracked down the radio schematic and no external components were needed, so now all I have to do is figure out how to wire it up. All of the materials I needed were probably either in my junk box or available at my local Radio Shack.

I opted to use one of headsets at the house, a PC gamer set from Turtle Beach. It had nicely padded ear covers, the sound was nice, the microphone has a gooseneck type boom, and the price was right. Also there is an inline volume control for the earphones and a mute function for the microphone. The headset had two plugs, one for the earphones and one for the microphone. The pink microphone plug is a stereo plug and has three connections. Using a DMM I found that the tip and ring were connected internally (0 ohms) so the signal and power share the same wire.

Also, the there is an INTERNAL blocking capacitor on signal pin (pin 1) so there was not need to add any external circuitry. I added the female half of a 1/4 inch mono cable to plug in a PTT device and the male half of 1/4 inch to a 3.5mm stereo female for a headphone adapter and I called it done. I plugged in the microphone connector; I plugged in 1/4 inch male into the headphone jack. After plugging in the headset and adjusting mic gain I made a few contacts. The mic gain was set about the same as the HM-36 and signal reports were near broadcast quality. I guess that will work. :)

Bill of Materials

  • 8 Pin Microphone connector
  • 1/4 inch mono cable, male to male
  • 3.5mm female stereo cable
  • 3.5mm female stereo connector
  • Heat Shrink
  • Colored Tape (Red, Green)

Assembly Instructions

  1. Cut cables to length, approximately eight to ten inches.
  2. Solder tip wire of 3.5mm stereo cable to Pin 1 of the microphone.
  3. Solder ring wire of 3.5mm stereo cable to Pin 2 of the microphone connector.
  4. Solder Pin 1 to Pin 2 of the microphone connector.
  5. Solder shield to Pin 7 of the microphone connector.
  6. This connects the microphone to the radio, but I wanted to be able to key it, too.

  7. Solder shield of 1/4 inch mono female cable to Pin 6 of the microphone connector.
  8. Solder center of 1/4 inch mono female cable to Pin 5 of the microphone connector.
  9. Screw the connector together, the microphone connector is done.
  10. Solder the tip of the 1/4 inch male to the ring and tip of the 3.5mm female stereo connector.
  11. Solder the sleeve of the 1/4 inch male to the sleeve of the 3.5mm female stereo connector.

    I soldered a 1/4 inch male mono connector to a 3.5mm stereo connector with the tip and ring shorted (stereo to mono adapter) for the headphones and stuck it into the heat shrink before I applied heat.

    A few pieces of colored tape to help keep connections straight completes the project.

    As a hand key switch I put an old momentary contact pushbutton in a piece of cardboard tube soldered to the other 1/4 inch male mono connector. Simple, but it met my needs

    Now if I could only find a foot switch...