GB594083A - Improvement in amplifiers for audio frequencies and method of deriving feedback voltages, useful for making sound records and other purposes - Google Patents

Abstract

594,083. Magnetic instruments. RADIO CORPORATION OF AMERICA. Sept. 13, 1944, No. 17489. Convention date, Sept. 13, 1943. [Class 40 (iv)] [Also in Group XL] An audio-frequency amplifier has a transducer coupled to its output and means are provided for translating the currents fed to the transducer into frequency modulated waves which are fed back in the form of audiomodulation currents to the amplifier to reduce distortion. Fig. 1 shows a recording system, the audio-frequency output from microphone 10 being fed through amplifier 8 to coils 3 and 4 wound round the upper and lower portions of armature 9 which is located between the polepieces of magnet 9<1>, the south poles (not shown) being on the opposite side of the armature to the north poles. Current flowing through the coils causes the armature and thus the stylus 1 to vibrate laterally and cut grooves in the record. The armature may be mounted on a shaft 7 to which is secured the holder 5 carrying stylus 1 or the holder may be bolted to the armature, Fig. 3, and the coils wound around the two, the armature 20 being shown laminated. The holder 5 is connected to ground and with a metallic plate 14 forms a variable condenser shunting the tank circuit of oscillator 11. Vibration of the stylus causes frequency modulation of oscillator 11, the output from discriminator 15 being fed back in degenerative sense to amplifier 8. The plate 14 may be embedded in a block of insulated material secured to one of the polepieces, Fig. 4 (not shown). Specification 594,077 is referred to.