| 摘要 |
PURPOSE:To prevent beat disturbance by reading beat cancel information from a storage means in relation to the channel selection operation of a tuner circuit to change over a switching frequency of a stepup transformer into other frequency not causing beat disturbance. CONSTITUTION:An on-vehicle acoustic device 21 consists of such devices as a tuner 22, an amplifier 23 and a speaker 26. A DC superimposition circuit 29 is provided at the post-stage of the tuner circuit 2 in the tuner 22 and superimposes a DC signal on an output of the circuit 2 in response to the beat cancel information sent from a channel selection circuit 30 incorporating a microcomputer 30a. The beat cancel information is stored in advance in response to a channel selection frequency. The superimposed DC signal is discriminated in the device 23 by a DC/AC discrimination circuit 28 and the result is fed to a changeover switch 26 via a DC detection circuit 27. A switch 26 is closed by the output of the circuit 27 to change over the oscillation frequency of the oscillator 12 in a DC-DC converter circuit 25. Thus,the beat disturbance attended with the switching operation of the converter is prevented.
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