Patent GB-383986-A (GB)
Title: Improvements in or relating to sound reproducing systems
IPC: G11B17/02
Filed: 1931-08-24
Abstract: 383,986. Reproducing music. HAM. MOND, J. H., Hesperus Avenue, Gloucester, Massachusetts, U.S.A. Aug. 24, 1931, No. 23764. Convention date, Aug. 23, 1930. [Class 40 (iv).] In the reproduction of sound from records on gramophones each record is provided with means for automatically pre-setting control devices whereby the intensity and tone qualities. of the reproduced sound is regulated. The apparatus may also be adapted for reproducing from records not provided with the said means for controlling the output, the controls in this case being regulated manually. As shown in Fig. 1, the turntable 37 is secured to a member 36 fixed to a sleeve 20 supported on ball bearings 24 and driven by the action of the poles of coils 14 .. 17 acting on a metal disc 18 fixed to the sleeve which is geared through worm gearing 22 with a governor. The sleeve 20 embraces concentric sleeves 25, 27 and a central rod 31 whose lower ends carry grooved collars 42, 43, 44 engaging pivoted levers 45, 46, 47 to move contacts 54, 55, 56 over potentiometers 57, 58, 59, and whose upper ends carry wedgeshaped plates 26 with which engage pre-formed radial slots provided in each record. The record is apertured to engage over fixed pins on the turntable, and when pressed down thereon the ends of the radial slots engage and depress the plates 26 and members carrying these to adjust the potentiometers 57, 58, 59 in accordance with the slots in the record. These potentiometer adjustments which are thus automatically set by each individual record when applied to the turntable correspond to the elements 65, 108 and 111 in the circuit shown in Fig. 5 for amplifying the output from the pick-up 64 before it influences the speaker 68. This circuit comprises amplifying valves 72, 73 supplied by a control valve 71 influenced from the pick-up 64 through the potentiometer 65, filter circuit 77, 78, 79 and resistances 75, 76. The voltage across the resistance 75 is automatically regulated in accordance with the output of the pick-up 64 by connecting a branch from that output circuit through an amplifier 82, filter circuit 85 and detector 83 with the opposite ends of the resistance. The voltage across the resistance 76 is automatically regulated in accordance with the output of the main amplifier the output transformer of which is connected through resistances 91, 92, filter circuit 93 and detector 94 with the ends of the resistance 76. Another branch from the output transformer acts through resistances 97, 98, a rectifier 99, and a rectifier 104 fed with alternating current from a source 105 and controlled by the potentiometer 108 from the record, to influence a solenoid 81 so as to vary condensers 77, 78 in a filter circuit 77, 78, 79. The collective effect of these controls in the grid circuit of the control valve 71 together with the further control by the potentiometer 111 influenced from the record control the input to'the amplifiers 72, 73 whereby scratch and undesired high frequency sounds are eliminated and desired modifications of reproduction are obtained. One or more of the levers 45, 46, 47 may operate to vary the capacity of a condenser instead of varying a potentiometer resistance in the circuit to attain the desired control.