Posted by
K1LI on
Jan 29, 2010; 3:03pm
URL: http://elecraft.85.s1.nabble.com/K2-connecting-a-condenser-mic-tp4480033p4480396.html
Thanks, Don.
Not knowing any better, I simply shorted the AF and MICBIAS when I connected
the mic to the K3. From what I can see in the K3 schematics, the only
bypassing on the MICBIAS line is 1uF (rev B, sheet 5 of 7, "Front Panel -
Miscellaneous"). Can I build the same resistor into the mic plug and use it
that way for both the K2 and K3?
Brian K1LI
On Fri, Jan 29, 2010 at 9:34 AM, Don Wilhelm <
[hidden email]> wrote:
> 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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