If it really is a simple condenser microphone, it will not work with only 5, or even 12 volts of bias.
It is almost certainly an electret microphone, which is a composite device, consisting of an electret transducer and a MOSFET pre-amplifier. The element is biased by the permanent charge on the electret, and the power supply is actually for the pre-amplifier. ----- 400k is too low for the element itself and too high for the FET, in a two wire configuration. I suspect a two wire configuration and that the reading is being distorted by reverse polarity or too low a measurement voltage. ----- Most, if not all, amateur use electret microphones are two wire devices, even though those for PC sounds use stereo plugs; the ring and tip are actually connected together, and the plug is just a trick to ensure that the bias is not applied to a dynamic microphone, which will use a mono plug. Applying 5 volts DC to one of these without either a resistor or AF choke, will create an AC short on the output, and, depending on how good the power supply bypassing is, you may get no output at all! ------- A two wire electret will not behave like a resistor. It will have the approximately square law characteristic of an FET drain, so you cannot use simple potential divider calculations. ------- The risk of a short would be due to a cable fault Non-interleaved top posting by list policy, not desire. -------- indicate where to interleave. 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 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. --------- > 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. > -- David Woolley "we do not overly restrict the subject matter on the list, and we encourage postings on a wide range of amateur radio related topics" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> ______________________________________________________________ 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
