GB390992A - Improvements in or relating to electrical sound recording apparatus - Google Patents

Abstract

390,992. Sound-recording circuits. RADIO CORPORATION OF AMERICA, 570, Lexington Avenue, U.S.A.-(Assignees of Dimmick, G. L. ; Westmont, New Jersey, U.S.A.) July 25, 1932, No. 20909. Convention date,'Aug. 6, 1931. [Class 40 (iv).] An electrical sound-recording apparatus is provided with an electrically-operated monitoring indicator which-has frequency characteristics substantially the same as those of the recording mechanism. The indicating apparatus, shown diagrammatically by Fig. 2, includes a galvanometer 1 which vibrates a mirror m and a light source 2, light from which passes through an aperture 4 and is then focused by a condenser lens 5 upon the mirror m. The reflected beam from the mirror m is further reflected by an adjustable mirror 6 and by a mirror 8 to impinge upon a viewing screen 9. The mirror 6 is adjusted by a member 7 so that in the normal position the reflected beam falls upon the mid-point of the screen 9. The output from the recording amplifier is supplied to transformers 11, 12 the transformer 12 operating the recording mechanism at 13 and the transformer 11 actuating the indicating apparatus. The galvanometer 1 is designed to have electrical and mechanical characteristics similar to those of the oscillating member of the recording mechanism and a resistor 14 is used to vary the sensitivity of the indicator to match that of the recorder. The apparatus is assembled as shown in Fig. 1a and is enclosed by a cover which is furnished with an internal screen for the light source 2 and with an aperture through which projects the member 7. An observation port in the cover allows the position of the light beam upon the scale of the screen 9 to be observed.