| 摘要 |
PURPOSE:To maintain the specified input levels to an RFAGC circuit for voice and to provide the improvement in C/N of output and S/N of a reproduced sound signal by detecting the presence or absence of the recording of a video signal and changing over the gains of head amplifiers for voice. CONSTITUTION:A drop-out detecting circuit 59 detects whether the outputs of heads 52, 53 to be used exclusively for video attain a reference level or not and the outputs are made reverse from the previous state if the outputs do not attain the reference level. The output from the circuit 59 is integrated by an LPF 63 and is inputted to a Schmitt circuit 64, from which an H level is outputted in the stage of recording the video signal and an L level is outputted in the stage of non-recording. On the other hand, the gains of the head amplifiers 67, 68 are controlled by the output from the circuit 64 and the gains are decreased by 12dB if there is no video signal as compared to the case when there is the video signal. The input levels to the RFAGC circuit 71 are thus made the same regardless of the presence or absence of the video signal.
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