| 摘要 |
PURPOSE:To improve the S/N ratio, by securing a combined use of the resistance and capacity of the time constant circuit in a gain control circuit for the resistance and by-pass capacity of a bias circuit each. CONSTITUTION:The transistors TR10 and 11 are provided between the emitter and the earth of the amplifying transistors TR1 and 2 plus 3 and 4 each via the emitter resistances 12 and 13, thus forming a constant current source. The reference voltage is applied to the bias voltage supply terminal E, and then the resistance 14, the temperature compensating diode 15 and the resistance 16 are connected in series to be earthed. The collector of the TR17 for control of the constant current source, the bases of the TR10 and 11 plus the terminal F of the time constant setting capacity 19 are connected to the joint between the resistance 14 and the diode 15. The base of the TR17 is connected to the gain input terminal B, and the emitter is earthed via the resistance 18. In such constitution, the current value of the constant current source varies evenly to the gain control input, and thus no amplified noise is produced to the output terminal D in case the input is supplied to the terminal A. As a result the S/N ratio can be improved. |
