Re: K2: connecting a condenser mic
Posted by
Don Wilhelm-4 on
Jan 29, 2010; 2:34pm
URL: http://elecraft.85.s1.nabble.com/K2-connecting-a-condenser-mic-tp4480033p4480235.html
Brian,
Is that a 3 terminal mic element? If so, then you can follow the
manufacturer's instructions and apply the 5 volts to the voltage
terminal on the element.
OTOH, most of these elements are 2 terminal, and the voltage should be
applied to the AF pin through a resistor - try 5.6k like the Elecraft
MH2 uses as a first trial, it will likely work because the resistance is
not critical.
If you try to connect the 5 volts directly to the AF terminal, you will
effectively bypass all the audio to ground. For AC signals, a power
rail is jst the same as ground because there are large bypass capacitors
on the voltage rail.
73,
Don W3FPR
Brian Machesney wrote:
> I have a condenser mic that is not on the list of "known" mics in the docs
> or on the Elecraft web site. I'm trying to decide whether to simply short
> the +5V to the AF when connecting my condenser mic to the KSB2, or to place
> a resistor in between. I am more concerned about potential long-term adverse
> effects on the mic element by operating it out-of-spec than I am concerned
> with damaging the K2.
>
> A DMM shows the DC resistance of the element to be 400 Kohms! Not really
> surprising, I guess, since a condenser mic is electrically similar to a
> capacitor.
>
> The manufacturer specs the mic element at 4.5Kohms and 1.5V to 9.0V bias.
> Applying the KSB2's +5V directly to the mic element's 4.5K ohms should
> produce 1mA drain, no sweat for the KSB2, and right in the middle of the
> manufacturer's applied DC voltage spec.
>
> The manufacturer's tech sent me a wiring diagram that shows a +12V supply
> with a series resistor between 470 and 2.2K ohms to the mic. The 470 ohm
> resistor would apply nearly 11V to the mic, if the mic element and the
> series act as a pure voltage divider. The 2.2K ohm resistor would produce 8V
> at the mic.
>
> The KSB2 schematic shows a 2.2uF electrolytic cap between the MIC AF and the
> rest of the KSB2, so I wouldn't think there's any risk of a short.
>
> Help from those in the know, please?
>
>
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