Modification of the new ICOM HM-36 microphone by SE5X Lennart Deimert. This is a detailed description with pictures and schematics how you easy can modify your new HM-36 to sound better.


Modification of the new
ICOM HM-36 Microphone




The first step is to figure out what type you have, the old or the new one.

The old version of the HM-36 has always sound good and has an electret microphone with three connections.
It is recognized by the t
hree wires, red, black and shield.  If it looks this way you got the old version and no modification is needed. This microphone is marked 'MADE IN JAPAN' or no marking at all.

This is a picture of the newer unmodified HM-36. Click on the picture for higher resolution.
Unmodified ICOM HM-36 microphone


ICOM HM-36 MADE IN CHINAThe new HM-36 entered the market at the end of 2007 and beginning of 2008. This new type has too less of the higher frequencies and too much of the low ones. On the back side of the microphone you can find  'MADE IN CHINA'.

The new type only have too wires connected to the element.  It is simple to modify the new type to sound as the old one.

1.  Remove R1, 1 kOhm and C2, 10 F.

2.  Change C1 from 0.22
F (sometimes schematic shows 0.33 F to 0.01 F  (equal to 10 nF or 10 000 pF)

These components are marked on the circuit board and easy to locate.

The C1 can be replaced with a tantalum or ceramic capacitor.
This is a picture of the newer HM-36 after modification. Click on the picture for higher resolution.
Modified ICOM HM-36
Remark; since R1 and C2 is in serial, only C2 has been removed from the circuit board


Hello Lennart.
Thanks for your help.  I tried the mod with a ceramic cap and the mic now sounds great.
Thanks again and Vy 73.  Mel.  M5ZZR.

Hello Lennart

I am ok with your mods. In your diagram the resistor R3 in both Old/New is 2k. When I checked my mic, it is reading 22k. Is that a possible typo or it is actually ought to be a 2k resistor?

I did the mods including R3 22k replacement with 2k. The power levels are by far better at levels, For example at microphone gain/comp on at 20% @100W, i can get an average output of 55W; before if I could make 20W, it was at a much higher voice level. ALC is now under respectable control.

I will write to Icom directly by mail and request a replacement mic as well; tech service said a replacement mic will not be offered. When I spoke to the hop where i got it from, they too were unaware that there is an issue with the mic. I just happened to be reading across various threads and found your article plus then WZ1V who noted the 22k discrepency. I comfirmed with WZ1V that i also have 22k issue.

If you can note in your diagram 22k issue as well and suggest that it match up to 2k; it will complete the overall changes in a single place.

Much appreciate your effort in putting the diagrams out there for us to read.

Sajid VA3QY
Dec 4, 2011

Hello Lennart:

I appreciate your info on the Web about HM-36.
I confirmed that the HM-36 bought on November 2011
also had 22kohm as R3. Replacing it by 2.2kohm
as well as the C1 revived the microphone :)

FYI and 73
Kenji Rikitake, JJ1BDX(/3) 


















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