I have a very old but apparently high quality mic, a Sony 'F-99B', just
rediscovered in my shed: 'One point stereo dynamic microphone IMP.LOW'
It proved useless when I tried it on my PC, in the usual mic socket,
presumably because of its low impedance. (My multimeter shows its left and
right connections as about 170 ohms.)
Can anyone suggest an inexpensive UK supplied mic transformer I can buy
please?
You might want to review the discussion at
http://www.audiobanter.com/showthread.php?t=118737
which captures a USENET thread from rec.audio.pro back in '09.
Based on what I read here,
- The F-99B is already supposed to have a "high-impedance" output
(i.e. it may already have a transformer in it). You may be
reading the DC resistance of the transformer coils, rather than
the audio-frequency impedance of the system.
- You're likely to need a separate amplifier stage to boost the
signal enough to operate into a PC's "mic" input. PC inputs
are usually designed to be used with active (buffered and amplified)
condenser microphones, which have a relatively high voltage output
(tens to hundreds of millivolts) and a fairly strong ability to
drive current. If the mic and its built-in transformer (assuming
it has one, as the discussion implies) won't drive the mic input
successfully now, adding an additional transformer stage may not
help... you'd gain voltage, at the cost of an even higher impedance,
and the input impedance of the "mic" receiver stage may load down
the source impedance too much.
- It may not be worth the effort... several discussions of the
F-99B suggest that it's not a terribly good microphone.
--
Dave Platt AE6EO
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