From: Norbert_Hahn@nospam.invalid   
      
   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   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)