| 摘要 |
PROBLEM TO BE SOLVED: To provide a capacitor microphone that suppresses variation of plate current in a vacuum tube as an impedance converter, has no possibility of dielectric breakdown between a cathode and a heater in the vacuum tube, without noise caused thereby, and suppresses power consumption while keeping appropriate sound quality, and also to provide an impedance converter therefor. SOLUTION: The impedance converter for a capacitor microphone is equipped with: a vacuum tube 30 that receives an output signal from a capacitor microphone unit 10 through a grid and with which the signal is output as an output from a cathode follower; an FET 35 which is in cascade connection with the vacuum tube 30 and defines a current flowing in the vacuum tube 30; and a bias circuit that applies a bias voltage to the grid of the vacuum tube 30. The bias circuit is a fixed one having: a first diode D3 that applies the bias voltage to the grid of the vacuum tube 30; a second diode D4 being connected in inverse parallel; and a bias resistor R7 for applying the bias voltage at a constant level to the grid of the vacuum tube 30 via the first and second diodes D3 and D4. COPYRIGHT: (C)2011,JPO&INPIT
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