[Elecraft] [KX3] MIC Bias has no effect

[Walter Underwood]

I saved this detailed note that was posted on this list a couple of years ago. Maybe Elecraft needs a KX3 FAQ with this info.

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Re: KX3 - Buzzing in headphones varies with MON level	 
Posted By: kk7p
Date: Wed Jun 20, 2012 12:49 pm 

I dragged out my CM-500 to test this.

The CM-500 gets its mic bias from BOTH the tip and the ring of the gray mic
connector. This is too bad, because the tip voltage is controlled by the
MENU:MIC BIAS ON|OFF but the ring is always biased by the PTT/UP/DN logic
supply.

To get around the problem, do the following:

1) MENU" MIC BIAS OFF

You will find you need a lot less Mic Gain for full ALC action. In my KX3, I
need about 30 if BIAS is ON, and 17 if BIAS is OFF, for full ALC.

2) Since the PTT/UP/DN is a digital logic supply, it may have some residual
noise that the CM-500 passes as audio to the tip of the connector.

Go to MENU: TX GATE and tap "1" to turn it ON then adjust VFO A for 01 or 02,
whatever it takes to kill the residual buzz.

In the case of my KX3 + CM-500, this cured the problem. And in Dave's case, it
might not cure the problem of noisy neighbors, but will allow the KX3 to better
ignore them!

73,

Lyle KK7P
----------

Thanks, Lyle.

wunder
K6WRU

On Apr 19, 2014, at 9:27 AM, "dmb at lightstream.net" <dmb at lightstream.net> wrote:

> I'm connecting a Yamaha CM500 headset to the KX3, and find that the
> microphone works properly regardless of the MIC BIAS setting (MIC BTN is
> set to OFF).
> 
> As I recall, the few times I used the CM500 w/ the K3, the MIC BIAS had to
> be ON or the microphone produced no output.
> 
> Any idea why the MIC BIAS setting doesn't seem to matter w/ the KX3?
> 
> 73, Dale
> WA8SRA
> 
> 
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--
Walter Underwood
wunder at wunderwood.org