| 摘要 |
PURPOSE:To solve complicated trouble in receiving a cable television broadcast (MTV) by providing a circuit comparing a sound output of a TV broad case and a monaural sound output of an FM broadcast and a logical circuit driven by the compared output. CONSTITUTION:The MTV for exclusive use of music program is led to a TV tuner 19 and its sound output signal 20 is brought into a constant level by a limiter circuit 14. On the other hand, the FM radio wave is led to an FM turned 5 and stereo sound outputs 6a, 6b are subject to monaural output by a limiter circuit 10 and the level is matched to the monaural sound signal obtained by the circuit 14. Then the output of the comparator 11 is zero. When the input signal is zero, the output signal of the logical circuit 12 is set to a high level. In turning on a simultaneous cast switch 13, selector switches 8a, 8b connect to terminals 2a, 2b for other acoustic device, for example, in the selector switches 7a, 7b, 8a, 8b and even when the switches 8a, 8b are turned on, the switches 7a, 7b being the reception mode of the FM broadcast are turned on forcibly.
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