| 摘要 |
PROBLEM TO BE SOLVED: To obtain a power unit of a microphone which is simplified is circuit constitution by incorporating a phantom power source together with a buffer amplifier, and free of a variation in an operation point caused by a variation in a bias voltage of the buffer amplifier and hardly affected by an external magnetic field. SOLUTION: The buffer amplifier is connected to an output circuit of the microphone, and also equipped with constant-current diodes 21 and 22 as loads, and biasing resistances 11 and 12 of the buffer amplifier are used in common as power supply resistances of a phantom power source. An input bias voltage of the buffer amplifier is used as a microphone-side terminal voltage of the phantom power source. The buffer amplifier uses electron tubes 1 and 2 as amplifying elements. The buffer amplifier has two amplifying elements which are connected symmetrically, and an output terminal of each amplifying element is wound around a primary winding of an output transformer 5. COPYRIGHT: (C)2008,JPO&INPIT
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