GB1004532A - Audio frequency transistor amplifier - Google Patents

Abstract

1,004,532. Transistor amplifying circuits; amplifier circuits. RADIO CORPORATION OF AMERICA. Dec. 18, 1962 [Jan. 2, 1962], No. 47830/62. Headings H3T and H4J. A signal translating system having a high impedance transducer in its input circuit is characterized in that a unipolar transistor has its gate circuit coupled to the transducer so as to derive the full output voltage. As described, Fig. 1, a gramophone amplifier for a crystal pick-up 5 has a tone control comprising capacitors 8, 10 and resistor 9 and a volume control 28 feeding a unipolar transistor pre-amplifier stage 12, the input impedance of which is high. The output from this stage is fed to driven amplifier 39 in the output circuit of which is a transformer 73 giving an impedance step-down in the order of 50: 1, and having a push-pull output winding. In order to maintain a low source impedance for the push-pull output stage, transistors 70, 71 are biased by a pair of diodes 91, and negative feed-back is provided over a first path comprising resistors 53, 54, 56 and capacitor 55, a second path comprising resistor 61 and capacitor 60, and a third path comprising resistor 61 and capacitor 60, and a third path comprising resistor 66 and capacitor 65. In a modification, Fig. 2, the driver stage is omitted and the transformer primary 74 is connected to the output of the unipolar transistor. The resistor 66 is omitted from the feed-back path 64, which is coupled to the electrode 19 of the unipolar transistor instead of the electrode 20, and the shunt resistor 61 in the feed-back path 59 is replaced by series resistor 96. The tone control circuit is replaced by capacitor 100 and resistors 101, 102 in the output circuit of the unipolar transistor 12. Specification 1,004,531 is referred to.