Phantom Power
Audio Empire wrote:
On Sat, 17 Apr 2010 14:58:30 -0700, Norbert Hahn wrote
(in article ):
[snip]
There is two more type of condensor mic which don't use DC at all:
Both types use a low voltage RF generated by a low-noise RF oscillator.
The mic capsule of a RF condensor mic is part of a resonant circuit
that modulates the frequency of the oscillator signal. Demodulation
yields a low-noise audio frequency signal with a very low source
impedance.
In the other type of RF condensor mic the capacitance of the mic
capsule is used to modulate the amplitude of the RF oscillator.
These were somewhat common back in the 1940's and 1950's but are rare (if not
outright non-existent) today.
Have a look at Sennheiser's MKH series. Sennheiser started the series
in the late 1980s in order to make low noise mics. MKH-20...-50 for
studio purposes were the start. MKH-60 was aimed at long distance
recording (video support). Later the MKH-46x series was added and in
2000 the MKH-80xx series appeared.
[snip]
On a related note, in the 1950's, a company called Weathers built a
phonograph pickup system that worked on this same principle. Weathers called
it the "FM Pickup" because it used RF modulated by the stylus moving a
capacitive element to generate the audio signal. The thing had to be bought
as a system and consisted of the "cartridge", the arm, and the RF box. It's
advantages were low tracking force (1 gram), very wide, flat frequency
response, and theoretically, low distortion (because the capacitive element
was push-pull). In reality, the tuning of the RF was incredibly touchy and
even simple things like changes in humidity and temperature could de-tune the
damned thing, at which point, intermodulation distortion went through the
roof. One also couldn't fit any other cartridge to the arm. A friend of my
father' had one (mono, of course) and as I recall, when it was working right,
it sounded better than anything else in it's era.
Thanks for this report!
Norbert
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