[Elecraft] Mic and headphone

[Jim Brown]

On 3/4/2014 5:32 PM, Don Wilhelm wrote:
> The microphone is similar.  It is a relatively low impedance source, 
> and it is operating into a relatively high impedance device (1k to 10k 
> for modern transceivers) and the voltage produced is the important 
> parameter.  Yes, high impedance microphones may not give the proper 
> frequency response curve, but other than that, no impedance matching 
> is normally required.  Modern microphones are in the range of 200 to 
> 600 ohms driving impedance.  I suspect yours is also in that range. 

Good advice. Almost ten years ago, I bought what was probably a 
Plantronics salesman's sample kit of five different combo headset mics. 
I cut the connectors off of them and installed my own XL-connectors, 
then made adapters to go from the mics to the radios that I owned.

The first task with each headset was to determine which wires went to 
the earphone and which to the mic. I did that simply by listening to the 
earset as I measured between wires with an ohmeter. I don't remember how 
I figured out which wire was common, but I did. :) In each adapter that 
I built, I added a suitable resistor between the bias terminal on the 
rig and mic input.

Once I had done that, every headset/mic worked with every radio. Some 
were more comfortable than others, but all got good audio reports. All 
of that was long before the K3 even existed. But with the K3, all that 
is needed is to figure out which wire is which, connect them to the K3, 
and turn on the bias. They are all electret mics, and electret mics tend 
to be fairly hot (that is, fairly high output voltage).

73, Jim K9YC .