| 摘要 |
PURPOSE:To mute the constant current source circuits of a differential amplifier by connecting constant current circuits in parallel with a differential amplifying circuit which amplifies recording signals, feeding the 1st constant current output back to the differential amplifier and applying the 2nd constant current output to a magnetic head. CONSTITUTION:The signal applied to an input terminal IN is amplified with a differential amplifier 57. The collector currents of transistors (TR) 59, 62 are changed by the collector voltage of a TR 34, and the differential current with a constant current source circuit 60 is fed back to a TR 35 through a feedback impedance circuit 47. The differential current between the collector current of the TR 62 and a constant current source circuit 63 flows as constant current to a winding 7. The output impedance of a constant current output stage 61 is high and no bias current flows to the constant current output stage. In the stage of muting, a TR 56 turns on and the circuits 31, 60, 63 turn off, and the recording signal currents do not flow to the winding 7 of a magnetic head 6. |
