| 摘要 |
PURPOSE:To prevent the occurrence of double recording by detecting the light transmitting through or reflecting from a disc and controlling a recording gate circuit depending upon the presence or not of reproduction signal. CONSTITUTION:A disc 15 is radiated by the laser light from a laser 1 and the transmitted light is detected with photoelectric detectors 8a, 8b. The voltage corresponding to the reproduction signal is detected through an amplifier 101 and LPF 102 and is then compared with a reference voltage in a comparator 103, whereby the presence or not of the reproduction signal is detected. In case there is the reproduction signal, and FF 105 is set by the output of the comparator 103 and an AND gate 106 is closed by the set output of the low level of the FF 105, thus the revolution detection signal generated at each one revolution of the disc 15 outputted by a revolution phase detector 15 is not applied to the gate circuit 21. Since the gate of the circuit 21 is not closed, the recording singal is not applied to a photo modulator 2 even if the recording switch of the circuit 21 is inadvertently turned ON. Hence, the occurrence of double recording is prevented. |
