GB574557A - Improvements relating to the reproductions from disc sound records - Google Patents

Abstract

574,557. Sound recording and reproducing apparatus. BRITISH THOMSONHOUSTON CO., Ltd., and CASTELLAIN, A. P. Aug. 24, 1943, Nos. 13809/43 and 693/44. [Class 40 (ii)] [Also in Groups XXXIX and XL] An auxiliary record carried by a sound record controls the degree of automatic volume expansion to be employed during reproduction. When applied to a disc record, the auxiliary record may be an annular ring of alternate light and dark segments 3, Fig. 3, the number of the segments corresponding to the control required for that particular record. Light from a source 5 such as a neon lamp is directed on to the segments 3 and reflected thereby on to a photo-electric cell 6 producing an A.C. component which is filtered out by a frequencydiscriminator 9. Records are arranged in a relatively small number of groups with a par ticular control frequency for each group so that the frequency-discriminator may be of simple type. The lamp 5 and cell 6 are mounted in casings making equal angles with the record, the assembly being supported on a hinged framework, Figs. 4, 5 (not shown). Alternatively, the auxiliary record may be an annular ring of sinusoidally-varying width. Fig. 1 shows an amplifier circuit with automatic volume expansion obtained by applying signals from a tapping on input resistor R1 to the grid of a control valve V2, the A.C. output of which is rectified at W1 and applied via a resistor R2 to the screen grid of amplifier valve V1. The tapping on resistor R1 and a further tapping on a resistor R3 in the controlgrid circuit of valve V1 are controlled simultaneously by relays operated by discriminator 9, Fig. 3. In a modified circuit, Fig. 2 (not shown), a fixed tapping on resistor R1 is connected to the control grid of a control pentode, to the screen-grid of which are applied rectified potentials representing the degree of volumeexpansion to be employed.