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
 


 
 


May 14, 2012

Hi Lennart,

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 mod.....

Thanks again and best 73,

Ron pa0rcl
www.pa0rcl.com



March 19, 2012

Hi Lennart,

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.
 
 
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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