Patent GB-388036-A (GB)
Title: Improvements in or relating to electrical musical instruments
IPC: G10H3/08
Filed: 1931-08-10
Abstract: 388,036. Electric musical instruments. COMPTON ORGAN CO., Ltd., J., Chase Road, Willesden, London, and BOURN, L. E. A., 22, Stanwell Road, Ashford, Middlesex. Aug. 10, 1931, No. 22591. [Class 88 (ii).] In an electric organ, the windings 4, Fig. 1, in which undulating currents are generated by phonic wheels 1, are loosely coupled to the loudspeaker S by tuned circuits t, to ensure that the currents are of true sine-wave form. The circuits of field windings 3 on the cores 2 are closed by stop-contacts 6. The circuit of the generator winding 4 for the fundamental of a note, and the circuits of similar windings energized by other wheels 1 for the harmonics of that note, are closed by contacts 5 all operated by the key. The tuned circuits t, which also eliminate key-contact noises, are connected in series between the grid and the filament of the first valve of the amplifier A. One tuned circuit t serves for the circuits w of a fundamental note and of such harmonics of other notes as are distant not more than a semitone or a tone. Fig. 2 shows the action of the stops S and keys K. Associated with each key is a set of sixteen cores 2, field windings 3, generator windings 4 and contacts 5 (four units of each set being shown in vertical columns), corresponding to the fundamental and fifteen harmonics. The field windings 3 of all the fundamentals (and similarly of each order of harmonics) are connected in series through resistances 7. Depression of a key closes all its contacts 5, but currents are only generated in such windings 4 as relate to field windings 3 in circuits closed by stop contacts 6. For instance, stop Sn closes contacts 6n completing the field winding circuits of the fundamentals and all harmonics of all notes of the scale, giving trumpet tone for any note sounded. Each stop makes its requisite contacts 6 through its own resistances 7, whereby correct additive effects are obtained. To prevent slight currents being generated in windings 4 although the corresponding windings 3 are not energized, owing to hysteresis in the cores 2, mechanical interlocks may prevent contacts 5 from closing so long as no contacts in the corresponding field winding circuits are closed ; or, according to the Provisional Specification; the windings 3 may be given slight reverse currents by the stops when in " off " positions. Stopcontact noises are prevented by a choke and a condenser connected to each field-winding circuit. A " tremulant " stop superimposes an alternating current of say 8-20 cycles per second on the amplifier input. A " celeste " stop combines with. a given note, harmonics that are either sharp or flat. Twelve spindles, representing the semitones of an octave, are geared together at speeds increasing in the ratio 12#2. Each spindle carries discs 1 producing all the octaves of a given note together with their harmonics, the discs on one spindle being respectively similar to the discs on any other spindle. To avoid providing a separate disc for each fundamental and each harmonic of every note, where a note or any of its harmonics are of the same frequency as the harmonics of a lower note on the same spindle, the same disc is utilized for a number of windings. The consequent grouping of generator windings on each disc is illustrated in Fig. 3 (not shown).