| 摘要 |
PURPOSE:To make reproduction operation stable and good by performing variable controlling of the constants of the differentiation circuit of a reproduction ammplifier according to the recording density of magnetic discs via FET. CONSTITUTION:The record of a magnetic disc is reproduced and is applied via preamplifier 2 and LPF 3 to an amplifier 5 which is connected to a differentiation circuit constituted by a capacitor C and resistances R1, R2 and amplifies the differentiation output corresponding to the input signal. The output of this amplifier 5 is processed in a comparator 8 to which a reference voltage is applied, then the sequare wave corresponding to the input signal is generated. When the connection of the parallel resistances R1, R2 which form the differentiation circuit is turned ON on the inside circumferentace of the magnetic disc and turned OFF on the outside circumference by applying an external signal 9 to the FET, then the differential constant changes and the rise of the differentiation signal becomes mild owing to the differential constant which is large on the outside circumference where the peripheral speed is higher and the recording density is substantially higher than that on the inner circumference. Hence, even if a high resolution head necessary for reproduction of high density records is used, the reproduction of the low density recording portion is also well accomplidhed and the reproduction operation takes place stably and well. |
