| 摘要 |
PURPOSE:To apply automatic control to the sound volume by detecting number of revolutions of an engine and applying automatic control to the gain of an audio amplifier by the detection output. CONSTITUTION:A level converting circuit 7 applies level conversion to an output voltage of a buffer amplifier 5 so as to compare the voltage with a reference voltage 10B at a voltage comparator 10C. A level converting circuit 8 applies the level conversion to an output voltage of a buffer amplifier 2 similarly so as to compare it with a reference voltage at a voltage comparator 10C. An analog OR gate 9 gives an output of the level conversion circuits 7, 8 to the voltage comparator 10C. An operational amplifier or a differential amplifier is adopted as the voltage comparator 10C and a voltage change appears at its output after number of revolutions of the engine or the speed of an automobile reaches a prescribed value or over. Thus, the sound volume is increased automatically when the number of revolutions of the engine or that of a wheel exceeds a preset value and the sound volume giving ease of listening even under such a state is adjusted automatically. Further, a source is listened quietly with a small sound volume at a low number of revolutions or at a low drive speed.
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