IC7000 HM151 Microphone Audio Mod

I've had the IC-7000 for over 6 years now and it wasn't until I was trying to contact 2O12L and 2O12W - the Olympic Special Event Stations - that I noticed the very poor quality of my audio. No one had told me in the countless QSOs I made over the years running mobile. I was making adjustments one day, feeding the 7K into a dummy load and using my IC-706MkIIg without an HF antenna attached on receive. Needless to say, after initial testing using default settings on the 7K, the poor quality I was hearing took me by surprise. It was awful. I tried different Transmit Bandwidth Settings and the narrower I configured, the worse it became. I sounded like I was using a megaphone at the bottom of a steel barrel. Searching around the internet, this was a big issue and disappointment by many operators - now including myself. I found this site by AB5N who does mic mods for this specific issue. I also found these instructions by WX7Y. I decided to use the instructions to mod my own mic.

To conduct baseline audio tests, I put the IC-7000 on a dummy load, all audio settings factory default, and compression off using the stock mic. I built an audio isolation cable to interface between the IC-706's headphone jack and the mic input on my Dell Inspiron 1525 running Ubuntu 11.10. The IC-706 didn't have an antenna attached and received signal was kept at S9. I made audio recordings before and after the WX7Y mod and also with WX7Y's recommended settings.

HM-151 Audio Testing Setup

Initial Audio Tests


Audio Test #1 Stock MIC
SSB TBW (WIDE) H (SSB mode) : 2900 Hz
SSB TBW (WIDE) L (SSB mode) :    100 Hz

Audio Test #2 Stock MIC
SSB TBW (MID) H (SSB mode) : 2700 Hz
SSB TBW (MID) L (SSB mode) :    300 Hz

Audio Test #3 Stock MIC
SSB TBW (NAR) H (SSB mode) : 2500 Hz
SSB TBW (NAR) L (SSB mode) :    500 Hz

The mod started with a static free work area. These are before photos of the mic; you can see the small hole just below the F-2 key.

Stock HM-151

Flip it over and remove the two screws holding the back on:

Stock HM-151 MIC Back

Carefully pry the back shell off:

HM-151 Mic Back Open

Remove the three screws that hold the circuit board to the front of the shell, carefully take the circuit board out, just be careful that you don't rip the rubber boot that protects the actual switch. The first part that will be removed C30:

HM-151 C30

Once removed, replace C30 with .22 uF capacitor:

HM-151 Mic C30 Removal

Moving up the board, the red oval is the mic element pads. I placed a purple oval around C1. I used solder wick to remove the original mic element and in the process also removed C1. Checking the IC-7000 Service Manual, C1 is a non-polarized capacitor, so I was fortunate that it didn't matter which direction it was reinstalled.
HM-151 Mic

Once the stock mic element is removed, compare it to the new PUI element. The original element is on the left. The polarization of the new element is the same as the original so just make sure it gets installed with the same orientation as the original.

HM-151 Mic Elements

WX7Y's instruction is to put a blob of hot glue between the mic through holes on the keypad side of the mic. I couldn't make a small enough blob so I put down a decent sized one and then trimmed to fit.

HM-151 Mic Element Hot Glue Blob

Install the new mic element so the pins just protrude through the board. Keep trimming the blob until the height is correct. Solder it down and keep it parallel to the board.

HM-151 Mic Element on Board

With the new mic element much higher than the original the silicon keypad needs to have the hole enlarged and some foam trimmed to fit. The foam I used was in the bottom of my XActo Knife blade tube. It was a tad larger than what I needed but I just trimmed it down to fit nicely inside the front of the shell. This material is very easy to cut with a sharp blade so go slowly.

HM-151 Mic Silicon Keypad

Foam installed:

HM-151 Mic Foam Screen

The hole in the front shell also needs to be enlarged. WX7Y's instructions were to drill two smaller holes on each side of the existing one. I decided just to enlarge the existing hole using the outline that's present on the inside of the shell.

HM-151 Mic Opening Enlargement

Replace the keypad, circuit board, and screw the back of the shell back on too. Here's the completed mic:

HM-151 Modification Complete



Post Modification Audio


So, what does it sound like? Glad you asked! These next three clips are done with the exact same settings as the stock mic.

Audio Test #4 Upgraded MIC
SSB TBW (WIDE) H (SSB mode) : 2900 Hz
SSB TBW (WIDE) L  SSB mode) :    100 Hz

Audio Test #5 Upgraded MIC 
SSB TBW (MID) H (SSB mode) : 2700 Hz
SSB TBW  (MID) L (SSB mode) : 300 Hz

Audio Test #6 Upgraded MIC
SSB TBW (NAR) H (SSB mode) : 2500 Hz
SSB TBW (NAR) L (SSB mode) : 500 Hz 


WX7Y Settings

WX7Y included his Transmit Bandwidth Settings so I made a few more recordings for quality assurance purposes.

MIC Gain about 30 to 50 %
Compression about 1 or 2

Audio Test #7 Ragchew 
SSB TBW (WIDE) H (SSB mode) : 2900 Hz
SSB TBW (WIDE) L  SSB mode) :    100 Hz

Audio Test #8 DX1 Like a Heil HC5
SSB TBW (MID) H (SSB mode) : 2900 Hz
SSB TBW  (MID) L (SSB mode) : 200 Hz

Audio Test #9 DX2 Like a Heil HC4
SSB TBW (NAR) H (SSB mode) : 2700 Hz
SSB TBW (NAR) L (SSB mode) : 300 Hz

Thanks to WX7Y for the instructions.
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modHM151DefaultMid.mp3
(226k)
Mark Schoonover,
Sep 3, 2012, 2:53 PM
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modHM151DefaultNar.mp3
(237k)
Mark Schoonover,
Sep 3, 2012, 2:53 PM
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modHM151DefaultWide.mp3
(247k)
Mark Schoonover,
Sep 3, 2012, 2:53 PM
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modHM151WX7YMid.mp3
(263k)
Mark Schoonover,
Sep 3, 2012, 2:53 PM
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modHM151WX7YNar.mp3
(263k)
Mark Schoonover,
Sep 3, 2012, 2:53 PM
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modHM151WX7YWide.mp3
(271k)
Mark Schoonover,
Sep 3, 2012, 2:52 PM
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stockHM151DefaultTBWMid.mp3
(247k)
Mark Schoonover,
Sep 3, 2012, 2:52 PM
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stockHM151DefaultTBWNar.mp3
(231k)
Mark Schoonover,
Sep 3, 2012, 2:52 PM
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stockHM151DefaultTBWWide.mp3
(238k)
Mark Schoonover,
Sep 3, 2012, 2:52 PM