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 <[email protected]> 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? >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
