| 摘要 |
An impedance converter for a capacitor microphone includes: a vacuum tube that receives an output signal from a capacitor microphone unit through a grid and with which the signal is output as an output from a cathode follower; an FET in cascade connection with the vacuum tube and that defines a current flowing in the vacuum tube; and a bias circuit that applies a bias voltage to the grid of the vacuum tube. The bias circuit includes: a first diode and a second diode that apply the bias voltage to the grid of the vacuum tube; the first diode and the second diode being connected in inverse parallel; and a bias resistor for applying the bias voltage at a constant level to the grid of the vacuum tube via the first diode or the second diode.
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