Boatanchors

Well, as you can guess the audio performance of the Chinese microphones have gone from bad to even worse. In Photo 2 you can see that in this design C2 has been removed. C2 when installed connects across R2.

Note that C1 the 0.33 ufd capacitor (C1) is directly across the microphone element. This cuts out all the higher frequencies and even muddies the low frequencies. A simple change will make a big improvement. Change out C1 with a .001 ufd capacitor and place the old 0.33 ufd capacitor (originally C1) in the C2 location on the PCB. This will place the 0.33 ufd across the 2K resistor and allow a broader audio response.

Here is a .wma file of the mic's audio before and after this simple mod. This file was made in a single "take" using a switch to change the circuit back and forth. In the file I say Japanese but I meant to say Chinese.

I hope this helps anyone that has this microphone.

Other HM-36 Modifications can be found on the Internet.

Bob Nagy - AB5N, provides a modification service that is top notch and at a reasonable in price.

You can search for Bob on the net, his more extensive modification does an outstanding job on the HM-36.


The ICOM HM-36 Microphone
I know this isn't really a boat anchor but the HM-36 microphone has been around for a long time and has recently gone under some major changes. Others in our community have been complaining about the performance of the newer HM-36 microphones and I was curious as to what changed. A search on the Internet provided me with a lot of interesting data. The original Japanese ICOM design is shown in Figure 1 below. Note the number of parts in this design, now look at the Chinese design shown in Figure 2. The Chinese design greatly reduced part count and with that the audio performance of the microphone. You can find several modification to the Chinese design on the web. See Figure 2 and Photo 1. I decided to open up my poorly sounding HM-36 to make one of the recommended modifications. Imagine my surprise when I opened the microphone and found a completely different PCB and an even more stripped down design. See Figure 3 and Photo 2 for what I found inside.
Figure 1
Figure 2
Figure 3
Photo 1 (Chinese design shown in Figure 2)
Photo 2 ( Chinese design as shown in Figure 3) *(Where did all the parts go ?)*
Well, as you can guess the audio performance of the Chinese microphones have gone from bad to even worse. In Photo 2 you can see that in this design C2 has been removed. C2 when installed connects across R2. Note that C1 the 0.33 ufd capacitor (C1) is directly across the microphone element. This cuts out all the higher frequencies and even muddies the low frequencies. A simple change will make a big improvement. Change out C1 with a .001 ufd capacitor and place the old 0.33 ufd capacitor (originally C1) in the C2 location on the PCB. This will place the 0.33 ufd across the 2K resistor and allow a broader audio response. Here is a .wma file of the mic's audio before and after this simple mod. This file was made in a single "take" using a switch to change the circuit back and forth. In the file I say Japanese but I meant to say Chinese. I hope this helps anyone that has this microphone. Other HM-36 Modifications can be found on the Internet. Bob Nagy - AB5N, provides a modification service that is top notch and at a reasonable in price. You can search for Bob on the net, his more extensive modification does an outstanding job on the HM-36.