| 摘要 |
PURPOSE:To keep the dubbing characteristics unchanged regardless of the dispersion of resistance values in an IC, by so constituting that an input resistance of an IC preamplifier is sufficiently taken higher and the dubbing characteristics can be determined depending on an externally mounted resistor and the voltage gain of the IC. CONSTITUTION:The titled circuit is provided with a resonance circuit consisting of an inductance of a video head 1 and a capacitor 3, and a dubbing circuit connecting outputs of an IC preamplifier 10 and the resonance circuit with a feedback resistor 4. Preamplifiers 5 are composed of a cascode amplifier consisting of transistors Q1, Q2 to the base of which reproducing signal from the head 1 is applied and differential amplifiers 17 and 18, a feedback circuit 6 is constituted with a common emitter amplifier, the emitter is connected to an external terminal 13 and the output is led to the output of the resonance circuit via externally mounted resistors 11 and 15. Thus, the bubbing characteristics are dependent on the voltage characteristics of the IC and the externally mounted resistors, allowing to keep the dubbing characteristics unchanged regardless of dispersion of resistance values in the IC. |
