| 摘要 |
PURPOSE:To make it possible that even person who sits on seat near an engine hear easily the broadcast, by adjusting automatically the sound volume of a speaker in accordance with the number of revolution of the engine. CONSTITUTION:The rotation of the engine is detected by a Hall element 8, and the detection signal is impressed to the base of a transistor TR16. Consequently, the collector current of the TR16 is increased or reduced in accordance with the revolution number of the engine. Thus, when the revolution number of the engine is larger, collector currents i1 and i4 of TRs 21 and 24 are reduced, and collector currents i2 and i3 of TRs 22 and 23 are increased. Since a signal current is superposed to the current i2, a large signal current is fed to a main amplifier 46 when the current i2 is increased. Consequently, the broadcast is not drowned by transmitted sounds of the engine to clear away the difficulty in hearing the broadcast. |
