Patent GB-503598-A (GB)
Title: Improvements in and relating to electrical musical instruments
IPC: G10H3/06
Filed: 1937-09-02
Abstract: 503,598. Electrical musical instruments. ROPOHL, F. Sept. 2, 1937, No. 24045. [Class 88 (ii)]. Relates to a keyboard photo-electric musical instrument in which each note is represented by a group of endless sound-lines 1a, of different quality corresponding to known instruments, on a rotating transparent cylinder I, inside which is a source of light 9, Fig. V, directed in the form of a beam onto one or more photo-cells 10 outside the cylinder. In order to select individual sound-lines of desired timbre from the note-groups, the light-beam is intercepted by a composite mask 41, Figs. VIII and XIII, arranged between the rotating cylinder 1 and the photo-cells 10, Fig. V, or 34, Fig. XIII. In this arrangement, each note is represented by six sound-lines of different quality, and the mask comprises six combs 41 having teeth.43, which are half opaque and half transparent. The space 42 between the teeth of the front comb covers a group of sound-lines and the teeth of the remaining five combs are relatively staggered so as entirely to fill the tooth-spaces of the front comb. To expose selected individual sound-lines of the note-groups, one or more of the combs 41 is or are drawn across the path of the light-beam by drawing or rotating stops 51, which rotate pulleys 50, carrying cords 44 connected to the combs 41 and passing over stepped pulleys 49, which guide the combs at a desired angle. The opaque parts of the teeth, which may be produced photographically, may merge into the transparent parts, to give a gradual variation in timbre. In Fig. XIII there is a single permanently illuminated elongated lamp inside the cylinder, the light therefrom passing through a narrow slit 32 into a series of chambers 52, each containing a photo-cell 34 and a condensing lens 33. The chambers are arranged sideby-side along the cylinder, each one corresponding to a single note and coacting with groups of sound-lines of the same pitch. Notes are played from a keyboard by switching photo-cells 10, Fig. V, or 34, Fig. XIII, into the lowpowered input circuit of the low-frequency amplifier 14, Fig. V, whereby disturbances due to keying are avoided. In Fig. V, a greater number of tone-qualities is provided by dividing each group of sound-lines representing a note into six sub-groups each controlling its own photo cell 10, the photo-cells being distributed helically around the cylinder 1, and energized by six common elongated lamps, each of which directs light through a condensing lens 9. Individual sound-lines of each sub-group are selected by the composite masking arrangement described above, the sub-groups themselves being selected either by illuminating the particular one of the six light-sources 9 corresponding to the sub-group required, or by pre-switching the photo-cells of the required sub-groups into the keyboard circuit, the lightsources being all permanently illuminated. Such pre-switching may be controlled by stopswitches, or the individual photo-cells may be connected to separate manuals. Note-keying is effected by a double key 12 comprising one key 12 for obtaining full-tones by switching the photo-cell into the amplifier circuit with a series impedance 17, whilst depression of a rear key 11 produces half-volume tones by switching the photo-cell in with a different impedance 18. Depression of the rear key 11 also operates the front key but the effect of the latter is cancelled by the opening of a contact 19. The impedances 17, 18 can be varied by pedal controls. The keys 11 and 12 may also operate an arm wiping over an additional impedance. The impedances may be in the form of resistances, condensers or inductances. The cylinder 1 is built up of a number of cylinders connected by rings 2, which bear on a number of rubber-covered rollers 4, driven through a belt 5 by a motor 6. The instrument may comprise several cylinders coacting with a single photo-cell group by means of light-deviating prisms.