[Elecraft] K3 DTMF tones

[Joe Subich, W4TV]

 > What is surprising, however, is that everything works equally well
 > whether MIC BIAS is On or Off.

Bias to the electret element is not supplied by mic line - it's supplied
from the tone generator IC!  The tone generator supplies voltage when
no buttons are pushed which enables the mic.  When a button is pushed,
mic voltage goes away and the PTT circuit is enabled.

> I would have thought that the voltage on pin-6 of the front panel
> socket would have gone off when MIC BIAS is set to Off, but that is
> evidently not the case.
K3 Mic bias is DC on the mic audio line (pin 1).  It has no effect
on pin 6.

73,

    ... Joe, W4TV


On 2/8/2018 5:23 AM, David Pratt wrote:
> I am delighted to report back that changing the wire from pin-5 to pin-6
> has done the trick. DTMF tones work fine on the K3 as do also the UP and
> DOWN buttons with MIC BTN On in the CONFIG menu.  The DTMF tones also
> work on the K2.
> 
> What is surprising, however, is that everything works equally well
> whether MIC BIAS is On or Off. I would have thought that the voltage on
> pin-6 of the front panel socket would have gone off when MIC BIAS is set
> to Off, but that is evidently not the case.
> 
> Thank you again, Joe.
> 
> 73 de David G4DMP
> 
> In a recent message, "Joe Subich, W4TV" <lists at subich.com> writes
>>
>> Elecraft and Kenwood reverse the pin used for +8V that powers
>> the DTMF encoder.  You will need to move the wire on pin 5 of
>> the Kenwood Foster plug to pin 6 to get the +8V from K3/K3s.
> 
>> The same is true if you want to use a Kenwood desk mic with
>> built-in preamp or active equalizer (e.g., MC-60A, MC-80, MC-85,
>> etc.) with the preamp or eq.
> 
>> 73,
> 
>      ... Joe, W4TV
>