| 摘要 |
951,058. Automatic volume control. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 20, 1960 [April 23, 1959], No. 13838/60. Heading H4R. In an audio amplifier embodying automatic volume control, control voltages corresponding to at least two frequency bands are derived from the output signal and are then separately used to control the amplification of the frequency bands. A signal from the output of amplifier 3 is fed into a high-pass filter 5 so that when the voltage amplitude of a high-frequency signal exceeds the bias voltage 7, the anode current of valve 15 is reduced with a consequent decrease of emission from incandescent lamp 17 and hence increased impedance of photoresistor 20. Consequently low frequency signals are passed by low-pass filter 21, 20 with a decreased attenuation relative to that of the high frequency signals. A high voltage low frequency signal passed through low-pass filter 9 similarly increases the impedance of photoresistor 19 with a consequent increase of the low frequency impedance of the filter-capacitor 25, resistor 19. Amplifiers 2, 3 may also be gain controlled over an intermediate frequency band or over all frequencies by a voltage derived from the output signal by diode 22 and filter 23; the tappings on the resistors in filter 23 are for varying the bias voltages 7, 8 with respect to the output voltage. |
