My Headset Microphone Adaptor

I’ve found that frequently it’s useful to use a headset rather than the hand mike. Unfortunately it’s not just a case of simply wring in a headset mike instead of the supplied mike, as most headset mikes are actually electret condensers, which need to be powered

The radio I have is a Yaesu FT-818ND, and fortunately there are a number of circuits out on the net for replacing the mike in an MH-31 handset with an electret. It is indeed fortunate that the FT-818 provides a 5 volt line to the mike.

The one that I used can be found at It uses the below circuit.

Electret Circuit


Now I’m not replacing the mike insert in the MH-31, but I would like to still be able to use the PTT, Up, Down and Fast buttons on it while wearing the headset (VOX isn’t for everyone). This means that I pass through pins 1, 2, 7 & 8 only.

I elected to buy a small box with two RJ45 sockets in it. The thought being that I’d use a small connector to run from the box to the transceiver and pass through everything except the actual microphone to the MH-31. I could then ad the circuitry to properly power an electret and run that to a 3.5mm socket that I could plug the headset mike in to.

I did have two major frustrations during the build.

First, Yaesu number their RJ45s in reverse to the way the sockets that I bought to.

The second had me going for some time. I just could not get any audio into the transceiver. This issue turned out to be mechanical. I was using a mono 3.5mm socket. The jack on the headset was stereo, with the mike wired to tip and ring. When I put that jack in the socket, the earth of the socket was shorting sleeve (earth) and ring; so the mike was effectively shorted out.

This is the finished unit.


Here is the inside while I was still having the mono socket issues.


I just plug the headphone side directly in to the headphone socket on the transceiver. I’m working on a simple switchable audio LC filter to place in the headphone line as well, but I’ll write about that when it’s done.

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