I shouldn't, Icom Mic Pre-amp

[LeapFrog]

Came across this Icom microphone, the 600 ohm impedance element is no longer around.
My question is, do you recognize what model Icom this came from?
I'm going to look up the model, I really am curious if this was powered by "phantom power" from the radio through the wire harness, originally this had a four pin end attached.
[photo=medium]4097[/photo]
[photo=medium]4098[/photo]
I am thinking of repurposing this pre-amp, I just need to power it (If it was powered beyond voice to begin with)

 

[bob85]

looks like the HM7 from the 80's, they came with IC-730 / 740 and other sets,

power is supplied to the amplifier through the audio wire.

 

[LeapFrog]

looks like the HM7 from the 80's, they came with IC-730 / 740 and other sets,

power is supplied to the amplifier through the audio wire.

Thank You bob85, I will look into those model number Icom radios for some more info.

When you say the audio wire that kind of confuses me a little bit, I thought that wire fed audio into the circuit inside the radio, as in one direction and very a low voltage line.

 

[Captain Kilowatt]

The audio line carries audio as well as a DC voltage. The DC is blocked from affecting things it shouldn't by using a capacitor. Caps block DC but allow AC to pass and audio is AC.

 

[bob85]

As CK said the audio wire that usually only carries AC audio in most other brand radios also carries DC voltage to power the amp,

never tried the HM7 on other sets but the icom desk mics of the era tended to sound very loud and bass heavy / muffled on other brand sets,

later ICOM mics are more inline with the rest of the industry for output level but still take power from the audio wire last time i looked.

 

[LeapFrog]

Thanks Gentlemen!
Just when I feel like I know something, BAM real knowledge enlightens this fool!

-Sam

 

[Onelasttime]

A lot of condensers for example do not have 3 wires just two and AC and DC where on the same wire with no ill effect the two do not interact at all. It is is almost or is like having two different sources at different freq.'s so far out of phase with each other that they are invisible to each other. That is how I think about it in my mind at least. I have both I have some that have 3 wires and some that only have 2 wires.

I am slowly changing my gear over to 8 pin universal mic connector on radio's I run condensers on. In this way I can run the power down the same industry standard pin and not have any issues and not have to give up or modify pin wiring for other function built into my mic. This way even if I want to run a condenser into the radio directly with out external processing I can easily do it. So a base can go mobile and a mobile can go to base no problem and all the mics will interchange. Radio's I use dynamic mic's on I either leave them in stock configuration or I put them to 4 pin Uniden to make emergency mic replacement easy and convenient as in any truck stop, gas station, Radio Shack or Walmart etc....

 

[Yeti Communications Ltd]

hm7 if used on a later icom that used a ecm mic (hand or bench) is night and day ..the hm7 will be alot louder (too loud) and sharper (because of the freq response of the dynamic insert) ...
my hm7 came with my ic251A (2m multimode) ..
when used on my ic720/751/735 and ic738 (all ecm) its exteremly loud and in most cases overdriven

yes i have tried on optima....not recommended

inversely using a ecm mic on the foremetioned ic251a the audio dropped alot although sounded ok it just did not make the ic251a shine (my 2m dx machine)

if the hm7 broke i would replace it with a motorola mic from a gm300 which has the same high gain output but with the flat response ecm insert