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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
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 three
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
Click on the picture for higher resolution.
The 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.
R1, 1 kOhm and C2, 10
2. Change C1 from 0.22
(sometimes schematic shows 0.33
µF) to 0.01
µF (equal to 10 nF or 10 000 pF)
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
Click on the picture for higher resolution.
since R1 and C2 is in serial, only C2 has been removed from the circuit
May 14, 2012
Just performed your mod on the China-made
HM-36 I got with my new ICOM IC-7200. Your
mod sure helps a lot, thanks for sharing it.
I left the 10 uF capacitor in place and just
took the 1k resistor out and used it to
replace the 22k resistor. Of course, I
replaced the 0,22 uF cap with a ceramic type
of 10 nF as you suggested. This cuts the low
audio spectrum effectively.
I wonder why Icom does not make it a factory
I came across your microphone mod page on the internet since I was
looking for a way to get better audio modulation on SSB on my IC-718.
Having looked and tried the mod for the new HM-36 mic, I noticed the
average SSB output was only around 50 watts unless I shouted into the
mic to get about 100 watts SSB output.
The mod you have for the new HM-36 mic where you replace the 0.22 uF
capacitor to a 0.01 uF capacitor seems to be incorrect. Dropping down in
value in capacitance in your mic mod would actually be like putting a
higher value resistor in line with the audio. After trying your mod, I
verified it. Here's what I did instead of replacing the 0.22 uF capacitor, I
replaced the 2K resistor with a 1K resistor and left alone the 0.22 uF
capacitor. Now the mic has very noticeable punch on SSB and modulates on
a higher average to 100 watts on my Icom 718.
My mic originally had the 22K resistor in it before and I was only
seeing 20 watts average output on SSB before. Now the stock mic
modulates the radio correctly.
Just wanted to let you know what I found after doing the mic mod on your
website for the HM-36.
Dale - K5WHR.
Thanks for your help. I tried the mod with a ceramic cap and the mic now
Thanks again and Vy 73. Mel. M5ZZR.
---------- 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
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
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
Dec 4, 2011
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 :)