There are two means of supplying bias for an electret (or preamplified)
microphone. The first, used by Elecraft in the K3 and by Icom, is to
simply add DC voltage to the microphone "hot" lead. The second, used
by the rest of the world is to use a "power adder" circuit to the mic
line and supply the bias externally.
The power adder consists of a capacitor between the mic element and the
microphone input of the radio (to prevent the bias from upsetting the
microphone amplifier) and a resistor connected to the junction of the
mic element and the capacitor. Power is applied to the other end of
the resistor from any available source which can be another pin on
the mic connector (pin 6 for Kenwood, pin 5 for Elecraft, pin 2 for
Yaesu/TenTec/Flex-radio) or even a battery. The resistor is not there
for voltage dropping, it is there to limit the current to the mic
element to a safe value and to prevent the internal impedance of the
power supply, particularly any filter or bypass capacitor, from
loading the mic (shunting the output).
> There is some confusion about Heil microphone/headsets like the Heil
> Traveler. That is also an electret, and should have bias.
Two solutions:
1) make up your own adapter that has no blocking capacitor and no
resistor. Turn on the "pin 1" bias in the K3.
2) Use a Kenwood HSTA but move the resistor on pin 6 to pin 5.
73,
... Joe, W4TV
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of David Yarnes
> Sent: Thursday, December 13, 2007 6:04 PM
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Cc: elecraft@mailman.qth.net
> Subject: Re: [Elecraft] Mics for the K-3
>
>
> Hi All,
>
> Actually, it is more complicated than that. First of all,
> you need to be
> sure you know exactly what kind of mike you have, as in
> electret or dynamic.
> Also, when referring to the "Pro-Set", you should be sure to
> distinguish
> between the Heil Pro-Set" with the HC4 or HC5 cartridges (no
> bias on those),
> and the Elecraft Pro-Set K2 (made by Heil, and it is the "IC"
> version) which
> does require bias.
>
> There is some confusion about Heil microphone/headsets like the Heil
> Traveler. That is also an electret, and should have bias.
> however, the
> adapter for that microphone to mate with a Kenwood, has a
> dropping resistor
> of some kind (I measured 2.2K ohms) between pin 5 and pin 1,
> which is how
> you get bias I guess on a Kenwood radio--using pin 5. But
> the Elecraft K3
> is shown as having 8 v. on pin 6, not pin 5. There is,
> however, something
> like 2.8 volts showing on pin 5 of the K3 microphone connector (front
> panel). I had some email exchanges with Don Wilhelm about
> using this mike
> (the Traveler), and he was concerned about how it seemed to
> be wired (via
> the "Kenwood" adapter). Accordingly, I am not using it, and
> am using an
> Elecraft Pro Set K2. I don't plan to use the Traveler until
> the confusion
> about the Traveler clears up. I may be wrong, but it seems
> to me that you
> don't need any connection on pin 5 or pin 6 (on the
> microphone) since the
> bias is apparently applied to pin 1 by turning on bias with
> the menu. So,
> maybe for Kenwood adapters, like the one the Traveler uses,
> one should maybe
> eliminate the pin 5 to pin 1 interconnection. Alternatively,
> maybe you
> should just make up your own adapter. Perhaps someone else
> can shed some
> light on this.
>
> Dave W7AQK
>
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