K6ARK Mini Microphones for KX3 and IC705

The MH3, the standard microphone for the Elecraft KX3 is rather big, and the Icom mic for the IC-705 is not much better. I was looking to replace those with something smaller.

There is a nice design for a 3D printed mini microphone by Adam, K6ARK. The 3D files are here:

https://www.printables.com/model/320559-mini-microphone-for-qmx-trusdx-usdx-kx2-and-kx3 

There are build instructions here: https://k6ark.com/mini-mic-build-instructions/

Now, I don't have a 3D printer, but a good friend was so nice to print me two of these mics, one in orange, one in white.

KX3

I built the KX3 model first, that was a piece of cake, just putting an electret element and a pushbutton inside, and connecting a 3.5mm TRRS cable ... ready !
I did not use the 3.5mm panel jack, but made a direct cable connection.
A long ferrite bead over the cable, near the connector, helps to keep RF out of the rig (see top picture).

This is the result after clicking both halves toghether.

IC-705

I studied the circuit of the HM-243 microphone, this looked a bit more complicated.

The shield is the main GND line. 

RING1 is a seperate line for the 8V DC supply, needed by the electret capsule.

TIP is the microphone signal, but also the PTT line. PTT is active when a 33k resistor is connected to ground.

Finally, RING2 is used for the four programmable buttons (A, B UP and DOWN), connecting four different resistors to that line.

While I was figuring out how to connect everything in such a small space, I got the crazy idea to add a second button to use as the 'A' button. It would enable me to send the first voice memory from the microphone, without even touching the rig.

I distilled my own circuit diagram from the original circuit.

I used a combination of SMD and normal components, and it looked like this:

Ferrite beads over the signal lines help to protect against RF ingress. Then, I covered everything with some heat shrink tubing.

The first test with the microphone was a bit of a disappointment. The microphone level was way too low, compared to the HM-243. 

I made a test setup, putting a speaker with a fixed 1 kHz tone, at 10 cm from the test capsule, and measured the output on my oscilloscope. I found output levels from 34 mV ptp to 84 mV ptp, quite a difference.
So I selected the one with the highest output, and that worked out OK. I got about the same modulation as with the original microphone.

I closed the box with some superglue, and this was the end result

Happy tinkering !

73,

Luc ON7DQ