| 摘要 |
955,796. Volume control. PYE Ltd. Feb. 6 1961 [Feb. 15, 1960], No. 5304/60. Heading H4R. In a volume control arrangement diodes 4 are connected one in series with each conductor of a 2-wire line and the conductance of the diodes is controlled by a low impedance bias source including a transistor 6 having its emitter con nected through a load to one pole (-) of a stabilized D.C. supply and its connector connected through a further load to the other pole of the D.C. supply, the base of the transistor 6 being fed with an adjustable D.C. voltage and the bias to the diodes 4 being taken from the collector of the transistor 6, whereby variation of the D.C. voltage applied to the base of the transistor 6 varies the bias applied to the diodes 4 and hence their impedance to an applied signal. In an automatic volume control arrangement (Fig. 3) the output of an amplifier 13 connected to secondary of transformer 2 is full wave rectified at 12 and the resulting output is applied to the base of transistor 6. The compression or expansion range depends upon the gain of amplifier 13, and the characteristic of the circuit may be varied by changing the value of capacitor 14 to give a different time constant. In a manual arrangement (Fig. 2, not shown) the base of the transistor 6 is connected to the slider of a potentiometer connected across the D.C. supply.
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