[Elecraft] Using a PC headset with K3, connections reverse at rear MIC jack?

[Alan Ibbetson]

Hello again. Thanks to so many people for their detailed help and 
suggestions. I seem to have solved the problem.

First: yes, Don is correct, this Plantronics headset microphone has tip 
and ring connected together, just like every other PC headset on the 
planet. That means my laptop offering bias on ring and Lyle offering 
bias+audio on tip makes no difference.

No I can't follow the herd and buy a CM500, because nobody stocks them 
in the UK and shipping from the US together with UK taxes makes the cost 
unreasonable.

This headset mic shows 6.8K to ground. I tried a different PC headset 
which shows 1K to ground and that one works perfectly with the K3 (and 
my PC of course). I'd also noticed that the Plantronics worked for a few 
seconds whenever I switched between rP.H bIAS and rP.H - ie when I 
toggled the bias in either direction, on or off.

So, on the grounds of "well, maybe I need to suck some current outa the 
K3 to keep a cap charged/discharged or bias the input correctly" I added 
a 1K2 across the Plantronics mic. Hey presto: we have voice.

Maybe someone who carries the KIO3 circuit in their head can educate us 
as to why the resistor bodge works, and perhaps put a range of values on 
it for the benefit of others who may tread this path with yet another 
flavour of not-Yamaha headset.

And now on to fiddling with TX EQ and suchlike. "Can you hear me, 
Mother?"....

73, Alan

On 29/10/2013 14:32, Alan Ibbetson wrote:
> Hi All,
>
> I'm a new K3 owner so please be gentle.
>
> I'm not a great SSB user so I want to use my cheap PC gaming/Skype
> headset on the odd occasions I use sideband. It has separate 3.5mm plugs
> for headphones and microphone so the K3's rear panel jacks seem the
> obvious place for connection.
>
> The Headset is a Plantronics 380. Although undocumented, I'd be
> astonished if the mic is anything other than an electret condenser element.
>
> The headset works fine on my IBM T60 laptop but doesn't work with the
> K3. And yes, I have switched on the bias.
>
> Poking about with a voltmeter and an unused stereo jack plug I find that
> the bias on my laptop is +5V ring to sleeve. On the K3 it is +7.5V tip
> to sleeve. I assume the audio is on the tip on the laptop and the ring
> on the K3. I've not seen any other comments about this on the reflector,
> but perhaps I have not looked carefully enough.
>
> Why would Elecraft do it this way, so these gaming headsets don't work
> without an ugly crossover adapter? Is there any non-soldering way to
> change the connections on the rear panel Mic jack?
>
> Thanks,
>
> Alan G3XAQ
>

-- 

Alan Ibbetson
alan at g3xaq.net