heil icm help

[1iwilly]

I need some help or advice. I have a Heil IC-Mic for my non-pro Icom 746, which has low-gain preamps. It only has options for treble (0 or +) and bass (-). My issue is that there’s a slight muffled sound when I speak. I've tried moving farther away from the mic, but that didn't help. If I increase the treble, it almost sounds like a "tiny tight underwear" effect—it's quite ridiculous! I've also changed the element, which improved it a bit, but the highs still sound fuzzy. Any suggestions?

 

[sp5it]

Try other microphone. Try ordinary electret capsule connected directly to the radio.

 

[1iwilly]

Try other microphone. Try ordinary electret capsule connected directly to the radio.

Thanks, i already tried that when i tried that element on my iCOM SM-20 desk mic, it sounds clean and clear, which leads me to believe i need a pre-amp for this Heil icm mic now to look for a donor that i care steal it from

 

[brandon7861]

I think the Heil puts out too much and is over driving your radio. That mic is said to have a strong output and pairs well with radios having weak front ends.

 

[1iwilly]

I think the Heil puts out too much and is over driving your radio. That mic is said to have a strong output and pairs well with radios having weak front ends.

Use of the Heil series of microphones
Most of the Heil series of microphones have too little output to sound good on an IC746 (IMHO) without employing a pre-amp. It's possible to turn the mic gain up, use the speech compressor and shout your head off but that's not ideal. You can even buy a suitable unit from Bob Heil. You can even make one. Ian G3SEK published a design in his "In Practice" article in Radcom It's a simple design and works very well, it can be made from junk box bits. Heil mic will take you there.

I subsequently discovered that most Icom radios, 746. IC756 and the pro's share very similar TX mic amp topography. It became obvious that Icom had increased the value of a resistor in the feedback network of UPC5023 on the MAIN unit in the later radios, presumably to allow after market microphones to work.

changing R1129 to 180KR brings the Icom 746 mic sensitivity up to that of the IC756Pro series.

here is an except from both diagrams, the resistor is surface mount but even if you havent got one, with care there is room to fit a 1/4W resistor.

N.B. IC706 and IC735 etc are the same. Icom Mic amp