| 摘要 |
An electroacoustic transducer system comprises a microphone working into a low-frequency amplifier for the energization of an a-c load such as, for example, a loudspeaker or a volume indicator at a control panel. Biasing voltage for the microphone and operating current for the amplifier are derived from a d-c source, via a phantom circuit including the output leads of the amplifier and through a coupler in cascade with a chopper; the latter includes a transistor conducting intermittently under the control of an adjustable pulse generator whose pulse width is varied by negative feedback from the integrated chopper output. An output transformer with a primary in series with the transistor has several secondaries each connected across a storage capacitor through a diode for the generation of a relatively high biasing voltage for the microphone, a relatively low driving voltage for the amplifier and, possibly, a further voltage used to vary the directional pattern of the microphone. To facilitate the establishment of different voltage levels, the development of the lower voltage is delayed-by the combination of a choke with a Zener diode, or by a thyristor-until the higher voltage has been reached by a transient occurring at the beginning of each cutoff phase.
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