[Elecraft] K2, PSK31 & microphone

[W3FPR - Don Wilhelm]

I would suggest leaving the resistor in place because your microphone needs
it -- it provides power to the electret element in the mic.

You could put a capacitor in series with the audio to the K2 to provide DC
isolation.  Somewhere between 0.1 uf and 1 uf would seem like the proper
range for the value.  The use of a capacitor will allow you to use
transformer isolation between the computer and the K2 - transformers from
defunct computer modems work well in that application.  Put the transformer
directly on the line from the computer (be certain to isolate any grounds
coming from the computer from the ground in your isolation box and the K2),
and the voltage divider and capacitor on the K2 side of the transformer.  It
should work FB.

You may be able to use an optoisolator instead of the transformer, but
beware of paths created by the grounding of the computer input jack, the
isolator power return line and the K2 ground - the grounds must be properly
isolated as well as the signals if you are to avoid computer noise.

73,
Don W3FPR

> -----Original Message-----
>
> I'm using Ham Radio Deluxe/PSK31 Deluxe software which handles the
> PTT, but I still need to connect from the sound card to the K2's
> microphone jack.
>
> I have the Proset-K2 headset that has an 8 pin adapter that accepts
> the monophonic Proset-K2 microphone plug.  I would like to use an
> audio ground loop isolator to connect the sound card audio out to the
> Proset-K2 adapter microphone plug.
>
> However, when I installed the Proset-K2, I had to install a 5.6K
> resister between 5V (pin 6) to the AF (pin 1)  on the back of 8 pin
> microphone adapter on the K2.
>
> I don't know the purpose of this resister; I assumed it was just a
> pull up.  Is it safe to leave this resister in place?
>
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