[Elecraft] Microphone for K2

[Jim Brown]

As some of you know, I'm in the pro audio business, so microphones are 
something I know a bit about. :)  At a recent hamfest, I bought three variations 
of Plantronics headsets made for use with cellphones. I paid $5 each; in a 
store they would likely fetch $15-$25. I've seen similar Plantronics models at 
Fry's Electronics, packaged for use with VOIP into a computer sound card, for 
$25.  For those of you who don't know, Plantronics is the originator of the 
miniature "Starset" headsets for telecommunications decades ago. They're a 
publically traded US company. 

Over the past two weeks, I've made adapters to use these headset/mic 
combos with my laptop for Echolink and VOIP, and also to run into my ham 
rigs. I haven't done one yet for the K2, but I just did one for the Icom 746 that I 
use on six meters. I am VERY pleased with the result -- on the air reports from 
critical listeners tell me that I have clean, punchy audio, the emphasized high 
end that works for good communications quality, and no breathe pops.  

The wiring to make these mics work with a K2 is quite simple. First, you need 
to cut off the plug and identify which conductors go to the mic and earphone. 
On my Plantronics units, white is the mic, red is the earphone, blue is common, 
and there is an overall shield that should be tied to the mic connector shell. To 
get bias for the mic element, add a 2.2K resistor between +8v and the white 
wire. If you want the earphone to work, you'll have to either bring receive audio 
to the connector or put a second connector on the mic to go to the headphone 
jack. 

If you're adapting it to a typical computer sound card, you'll also want the 2.2K 
resistor from wherever it shows up on the computer's mic input to the "hot" mic 
lead. It's no problem fitting a low wattage resistor into a Switchcraft 1/8" plug. 
It's trickier fitting it into the 8-pin plug used on the K2. 

Jim Brown  K9YC