[Elecraft] Questions on Yamaha CM-500 boom headset with K3

[Don Wilhelm]

Rick,

I would wager that your microphone ties the tip and ring together. If 
you look at the 'pinout' for the KX3 microphone (page 5 of the manual) 
you will see that Ring 1 is PTT/UP/DN.  If that pin is grounded, it is 
the PTT function, but if there is a resistance to ground on that ring, 
you will have either the UP or DN function depending on the value of the 
resistor.
Apparently the voltage introduced by applying bias is causing your KX3 
to interpret that level as either UP or DN (and it keeps repeating).

If you turn off bias, the the 'bias' voltage is supplied by the residual 
voltage from the PTT/UP/DN detection circuit in the KX3. Although that 
works, the voltage source being used for that bias is sufficient for the 
microphone element, but it is 'dirty logic voltage' which can give you 
noise in the microphone input.  Turning on the KX3 Noise Gate can help 
reduce that noise.

I built an adapter for my CM-500 (which also connects the tip and ring 
together) to eliminate that connection - one can use a stereo jack and a 
stereo plug with the tip of the jack connected to the tip of the plug 
and the shells connected together (no connection to the ring).  I built 
my adapter with a 4 circuit plug and brought out the logic ground 
(ring2) and ring1 to a switch that I use for PTT, but that is not a 
requirement, just my desire.

BTW, tying the ring and tip together is not a problem for the K3 because 
the K3 jack has no connection to the ring (that is why it is marked 
"Mono" - the jack is actually stereo.

73,
Don W3FPR

On 2/28/2013 9:15 AM, Rick Robinson wrote:
> This may be apples to oranges, but, I use a Pyle headset with my kx3 and
> mine works with or without mic bias. But.... if I have the mic bias off the
> radio goes into scan mode. Don't know why. Just thought I'd mention this in
> case your K3 acts the same way....Rick
>