GB548357A - An improved arrangement for the reproduction of sound - Google Patents

Abstract

548,357. Gramophone reproducing circuits. KOLB, O. K., and BOSTON, D. W. April 4, 1941, No. 4536. Addition to 473,256, [Group XXXVIII] [Class 40 (iv)] [Also in Group XL] The reproducing arrangements of the parent Specification in which volume expansion is effected under control of an auxiliary track in one or each sprocket hole strip of the film is modified by providing one or more amplifiers in addition to the main amplifier and using the auxiliary track to control the additional amplifying arrangements alone or in conjunction with the main amplifier. The additional arrangements may be capable of large output and brought in automatically to deal with loud passages. All the amplifiers may serve the same or different loud-speakers, or low frequencies may be fed to the same loudspeakers and high frequencies to separate ones. The additional amplifiers may deal with a restricted frequency range. As shown in Fig. 1, sound currents from cell C and control currents from cell C1 and, if two control tracks are used, from cell C2 are fed to the usual fader F, the sound currents being amplified by head amplifier HA. The currents then pass to a control unit CV which supplies the main and auxiliary amplifiers MA, AA as described with reference to Fig. 3. The control current which comprises modulated sprocket hole frequency (96#) is applied to valve V1 the output of tuned transformer TRI being rectified at R1 and applied over filter FC1 and the secondary of sound transformer TR2 to the grid of valve V2 which supplies the main amplifier MA and is biassed by a tapping from battery B1 over rectifier R2 which limits the control voltage applied to V2 to prevent overloading. The control voltage is also fed over a further smoothing circuit FC2 to valve V3 which receives sound currents from transformer TR4 and is biassed in a manner similar to V2 except that it does not come into operation until V2 is fully loaded. Valve V3 supplies the additional amplifier AA and, to prevent reproduction of valve noise when V3 is quiescent, the output circuit of AA may be completed by a relay RL when V3 is in working condition. In the modification, Figs. 2 and 4 (not shown), in which only the additional amplifier is controlled, the control circuits of the valve feeding the amplifier are similar to those of V2, Fig. 3.