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 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
unmodified
HM-36.
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.
1.
Remove
R1, 1 kOhm and C2, 10
µF.
2. Change C1 from 0.22
µF
(sometimes schematic shows 0.33
µF)
to 0.01
µF (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. |
|
 |
 |
| 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 |
