MH3 Microphone Freq Response Improvement

[k9jri]

I received my new MH3 yesterday and was quite disappointed in the poor audio reports.  Excessive bass and very few highs.  The bass was easily rolled off with the KX3's TX Equalizer but the highs were just missing.  One of the gang shot a panadapter picture which showed almost nothing above 1800 Hz.

The cure was quite simple:

If you open the plastic case you will see a white circle screened on the circuit board.  It is obviously a place for a large capacitor with the plus lead having been marked.  It has two holes for mounting the capacitor and by following the foils it is easy to see that it is in parallel with the existing R/C frequency shaping circuit installed on the board.

 Solder a strap (small U shaped wire inserted in the holes) across the capacitor mounting location and you are done.

On-the-air reports were that my audio was back to normal with only a minor roll off of the lows below 200 Hz.

The receive panadapter image was reportedly back to what I normally looked like with my other mics and similar to the response from the Flex-5000.

Give it a try..... nothing destructive about the mod at all.

73 - Mike - K9JRI

[k9jri]

I have a follow up to the modification:

On the air testing indicated that while the highs were improved some the bass was still excessive so another try was warranted.  I did find a helpful article correcting the same issue in the recent version Icom HM-36 which is a very similar mic.

I removed the shorting strap across the entire original RC circuit (2K with .3 in parallel) and also removed the original .3 SMD in parallel with the 2K resistor.  I then placed a .01 mylar in the same position that the shorting strap had used and the highs were increased significantly without changing the lows much at all.  This results in 2K with .01 in parallel for the frequency compensating network.

It receives good reports now and looks fairly full across the entire 3kHz. bandwidth my buddies panadapter is looking at.

My EQ settings are:
3.2 = 0
2.4 = +3
1.6 = 0
0.8 = 0
0.4 = -3
0.2 = -6
0.1 = -9
0.05 = -12

Very 73 - Mike - K9JRI

[ke9uw]

Filing this

Sent from my iPad

On May 24, 2015, at 6:46 PM, k9jri [via Elecraft] <[hidden email]> wrote:

I have a follow up to the modification:

On the air testing indicated that while the highs were improved some the bass was still excessive so another try was warranted.  I did find a helpful article correcting the same issue in the recent version Icom HM-36 which is a very similar mic.

I removed the shorting strap across the entire original RC circuit (2K with .3 in parallel) and also removed the original .3 SMD in parallel with the 2K resistor.  I then placed a .01 mylar in the same position that the shorting strap had used and the highs were increased significantly without changing the lows much at all.  This results in 2K with .01 in parallel for the frequency compensating network.

It receives good reports now and looks fairly full across the entire 3kHz. bandwidth my buddies panadapter is looking at.

My EQ settings are:
3.2 = 0
2.4 = +3
1.6 = 0
0.8 = 0
0.4 = -3
0.2 = -6
0.1 = -9
0.05 = -12

Very 73 - Mike - K9JRI

---

If you reply to this email, your message will be added to the discussion below:

http://elecraft.365791.n2.nabble.com/MH3-Microphone-Freq-Response-Improvement-tp7603440p7603492.html

To start a new topic under [KX3], email [hidden email]
To unsubscribe from [KX3], click here.
NAML

[k9jri]

After looking at the curves that the original RC network, the shorted out RC network and the final reduced capacitance RC network provide the obvious conclusion is that the built in KX3 TX Equalizer has far more than enough range to accommodate the desired MH3 EQ changes.

It must be that I am not using the built in EQ correctly or in fine enough increments or using the EQ bands in the proper order.....  or.....

Any suggestions on how to correctly implement the KX3's TX EQ?

73 - Mike - K9JRI