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Thursday, October 20 • 9:00am - 9:20am
Improved condenser microphone impedance converter using an operational amplifier

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Condenser microphones were invented in 1916 then commercialized by Neumann in the 1920’s Today's studio condenser microphones are all improvements from the original design. The impedance converter is necessary as the voltage must be sensed with minimal current drain. Typically a 1 Gigohm resistor is used to develop the voltage. Historically the first active electronic element was a vacuum tube. In 1965 Schoeps released a microphone with a Field Effect Transistor (FET)

The output drive electronics are needed to provide a low impedance balanced to the microphone preamp or recorder input. Tube circuits used a transformer. The original Schoeps circuit used two PNP transistors as emitter followers after the FET to add current drive capability. To this day, most condenser microphones use a variant of the Schoeps circuit or something with a single FET and a different output topology. The author has identified a low noise, low distortion FET input operational amplifier (opamp), the OPA1642 which adds the benefit of low quiescent current allowing for a dual opamp to be supplied by existing P48 phantom power. The resulting design features significantly lower total harmonic distortion than existing circuitry. This paper will explore the history of microphone electronics culminating with this design.

avatar for Jules Ryckebusch

Jules Ryckebusch

Chief Listening Officer, Sound Sleuth
Jules started his adventure in audio and electronics at age 16, in the heyday of what is now Classic 70s rock, when all his friends’ wanted guitars. Being the science geek that he was, he instead bought a kit, built his first analog synthesizer, and learned analog electronics as... Read More →

Thursday October 20, 2022 9:00am - 9:20am EDT
  Transducers, Papers Oct 19 & 20