| 摘要 |
PURPOSE:To increase the margin of a signal of a music-selection sensor and a reference potential against temperature characteristic, external disturbance and noise by providing a signal amplifier for music-selection sensor provided with an amplification factor changeover device so as to attain a broader setting range of reference potential of signal level. CONSTITUTION:A light irradiated from a photodiode 1 is reflected on a turntable face or a record disc face, received by a phototransistor 2, a photoelectric-converted output is inputted to the amplifier 17 with an amplification factor switching device having an amplification factor of N and inputted to a signal level discriminator 10. When the potential of a signal inputted from a reference potential C is high, it is discriminated as the absence of a record disc, and when the signal potential is lower than the reference potential C, it is discriminated as the presence of record disc, the amplification factor of the amplifier 17 is set to 2N so as to discriminate the information relating to the inter-music position and a sound groove position |
