| 摘要 |
PURPOSE:To obtain accurate reproducing signals at the time of reproducing at standard speed and high speed by switching the characteristic of an amplifying circuit in interlocking with the switching of a reproducing speed. CONSTITUTION:The output of a four division type optical detector 15 in a pickup 15 passes through I/V conversion amplifying circuits 17 and 18, is added, is inputted to the negative terminal of a wide band amplifier 19, and the output is fed back in a circuit 20, whereby a positive terminal is earthed. The feedback circuit 20 consists of a resistance R, a capacity C and a transistor Q. When the signal of an H level is fed to the base 49 of an element Q from a reproducing speed control circuit 43 at the standard speed for reproduction, the element Q is turned on, and the frequency characteristic of the amplifier 19 attenuates more than 700kHz. When the signal of an L level is inputted to the terminal 49 at the twofold speed of the standard one for reproduction, the element Q is turned off, and the frequency characteristics of the amplifier 19 are decided in R3-R5, C1 and C2, and they attenuate more than 1,400kHz, whereby the optimum characteristics can be obtained. With such a constitution, the accurate signals can be obtained at either speeds. |
