More punch MH-31
This page was last updated : 29-Jul-21 14:53:08
For the QO-100 setup I made a headset adapter (link) based on the Yaesu MH-31 Electret Condenser Mic Modification (link) which is giving a nice punch in SSB with very low SSB Microphone Gain on my FT817ND and FT818.
Based on that experience and advise from Stephan DM5TU (link) to modify my MH-31 microphone with a electred condenser mic, I decided that I wanted to give it a try. But instead of modifying my original MH-31 I ordered 2 MH-31 clones from AliExpress (link) to modify.
Schematic taken from Universal-Radio (link) so not my schematic.
Step 1 : take it apart.
Step 2 : de-solder the microphone element wires.
Step 3 : flip PCB
Step 4 : remove wires from switch, capacitors and resistor.
Step 5 : use de-soldering wick to clean contacts.
Note : the PCB design from this clone isn't as my original Yaesu MH-31,
TODO : add photo of original MH-31 PCB.
but the good news is that for this PCB you don't need to cut PCB tracks and can start installing components right away.
Step 6 : install capacitors and wire
- 1nF on location R1
- 47nF on switch contact to corresponding PCB pad
- 1uF on switch contact to corresponding PCB pad (negative lead to PCB pad)
- one wire to center contact to corresponding PCB pad.
Step 7 : install wire between outer switch pads on bottom of PCB and 8K2 resistor as shown below (between C pad connected to center of switch and pin 6 of RJ45 connector).
(check for shorts when done)
Step 8 : to hold theElectret Condenser Mic I 3D designed a holder which has the same size as the original Dynamic microphone element.
I used part of a kitchen sponge, used scissors to it to shape, and use my soldering iron to burn a hole in it to hold the element. Soldered 2 wires to the element and pulled the wires through the sponge (please be sure to use the correct polarity)
Step 9 : place sponge with microphone element in 3D printed holder and glue the 3D printed holder to the PCB (blue = ground, yellow = mic signal).
Ready for testing.
I setup the SSB-MIC-Gain on my FT818 to 30 and the rig is now giving a nice strong signal on the QO-100 without having to talk hard.
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