FT817 Mike Mod à la M0UKD

I replaced the stock dynamic microphone element in my MH-31 microphone with an electret element, as described originally by M0UKD. As far as I can tell, it works at least as well as the original microphone.

The stock mike never impressed me, so I had the W4RT voice booster installed. I did not notice any improvement, but the mike picked up RF on occasion. Signal reports deteriorated over time and finally the microphone seemed to stop working altogether.

Front side of modified microphone board.

It appears that the original mike element failed, so I chucked it and the modification in the trash and followed instructions per M0UKD, just taking note to reverse the polarity of the electrolytic cap so that the positive side faces the +5V phantom power.

I tweaked the layout a bit:

  • I used existing holes for the two switched capacitors.
  • A short run of 30 Ga wirewrapping wire worked nicely to bring power up the side of the microphone.
  • The electret element I had on hand looks like it was meant to mount on a circuit board and had 0.1″ spaced leads, so I used Dupont connectors. It can be detached again if necessary and it avoided applying heat to the element it self.
  • I just hot-glued the microphone in place. I don’t know if adding a lot of wadding around it really helps anything.
  • I forgot to add the last 1nF capacitor until after I had screwed it together, luckily, there’s a convenient place to tack it down just below the switch.
  • As others have recommended, I removed the metal weight from the microphone. Less to carry up SOTA hills.

I tested the modified microphone into a dummy load, with pickup by a nearby receiver in both SSB and FM modes. Voice quality seemed fine in either setting, so I tweaked the respective microphone gain settings on the FT817. Hopefully, I’ll have a chance to try out the new microphone “in the wild” in the next week or two.

Back side of the microphone, for testing. Missing the 1 nF capacitor.
Back of the microphone, now assembled, with 1nF cap (102) added.
Microphone “hot snotted” in place.

2 thoughts on “FT817 Mike Mod à la M0UKD”

  1. fellow ham here. I came across your blog page about the Yaesu mic mod. Thank you so much for sharing your knowledge.
    I am not super savvy with resistors and capacitors myself and i was wondering if you can help me identify what i am doing wrong with my mic mod.

    I do use an electret mic, just not the same way you would implement it in the MH31 housing.

    I am using instead an old phone handset.

    Although same thing.

    MIC to RJ45 connection on my FT-897

    I’ve supplied the 5V to the signal line via the right pin from my RJ45. and the mic work perfectly. I do want to include the 1nF capacitor to the mic connection and the 8K2 resistor on the line. as well

    The moment I add the capacitor to the 2 endings of my mic element the mic doesn’t work anymore… and I don’t understand why….


    I was hoping you can give me some tips regarding it.

    What I am doing wrong?

    Thank you very much!!!

  2. Hi,

    Are you sure that the phone handset microphone is an electret element? As I recall, phones (like of western union vintage) used carbon microphones, i.e., resistive microphones. If that’s the case, this won’t work as the electret microphone is electrically a capacitor rather than a resistor. I might be wrong on this — perhaps more modern phones did use electret elements. Sorry I don’t have anything for specific for you! Hope you get it working one way or another! – 73 de Jack 5B4APL / AI4SV

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