[Elecraft] [K3] front phones socket duability

[Lyle Johnson]

> In fact, I think it stays in all the time with this setting.
>> Set CONFIG:SPKRS = 2 and then it won't drop out

Here is what is happening.

If the DSP believes there is a monophonic listening channel in use 
(SPKRS = 1, as in using the internal speaker and headphones not plugged 
in) then all audio is folded in the left channel (which drives the 
speaker), and the right channel is a duplicate of the left (in case you 
have stereo headphone spluged in and SPKR+PH is set to YES).  That way, 
if you had the sub-reciever, for example, piped to the right and the 
main receiver piped to the left, you can hear both receivers in the speaker.

Most external speakers these days are mono, and there is no "ring" 
terminal on the plug: it just has a tip and a shell.  When you plug such 
a connector into the K3 external speaker jack, you are *shorting* the 
right channel.  Not damaging, but not a Good Idea either.

So, the KIO3 board has a relay in series with the right channel output 
to the speaker jack. If you have SPKRS = 1, then the relay remains open 
(to disconnect the right channel speaker amplifier from the external 
speaker jack) and it is safe to plug in a mono plug to the external 
speaker jack.  And the radio will operate with identical audio in the 
left and right channels, so your stereo phones will work properly.

If you set SPKRS = 2, then the relay closes, right channel audio is 
passed to the stereo speaker jack (since you specifically told the radio 
you were not plugging in a mono plug into the jack by manually setting 
SPKRS = 2), and stereo audio is created as appropriate.

More than you ever wanted to know, but there it is.

73,

Lyle KK7P