Patent GB-527080-A (GB)
Title: Electrical organs
IPC: G10H1/043
Filed: 1939-03-16
Abstract: 527,080. Electrical musical instruments. BALDWIN CO. March 16, 1939, No. 8482. Convention date, March 17, 1938. [Class 88 (ii)] [Also in Group XL] An electrical musical instrument comprises sources of electric oscillations of complex wave form, the oscillations being related as the notes of the musical scale, a set of means including switches, e.g., key switch Sk, Fig. 8, for feeding oscillations from the sources to a collector or header 18, Figs. 8 and 9, at least one further set of means including switches, e.g. Sk, for feeding oscillations from the sources to at least one further collector or header 19, an output system 29, R59 &c., a number of electrical paths from the collector or header to the output system and a number of further electrical paths from the further collector or header to the output system, each of such paths including a switch, e.g. stop switch Sts, and linear means for modifying in predetermined frequency ranges in the audio system the harmonic content of oscillations passing through the paths. Fig. 1 shows a group of glowdischarge oscillators O1, 02 ... in cascade, yielding one note and its octaves, each oscillator having a heated cathode K and applied negative grid bias. The master oscillator O1 is highly stabilized by a tuned circuit L1, C1 as in U.S.A. Specification 2,046,463, and by an inductance L2 magnetically coupled to inductance L1 transmits oscillations to the grid of oscillator 02, the inherent frequency of oscillator 02 lying between one and two octaves below the frequency of oscillator O1. Oscillator 02 is connected to ground by its cathode through a resistance R4, and by its anode through the condenser C2 and a network 3, and it is compelled to oscillate in phase with and at a frequency exactly an octave below oscillator O1. Oscillator 03, whose grid is connected to the resistance R4 of oscillator 02, is similarly stabilized at a frequency exactly a further octave below. A (high) note and its (lower) octaves are respectively carried from resistance R10 by leads " C " 1, " C " 2 ... , eleven other similar cascade sets supplying the remaining eleven notes of the scale and their octaves. Variations and changes in tube characteristics can be substantially eliminated by resistances R5, R6. The network 3 modifies the complexity of the oscillations, Figs. 3A, 3B respectively showing the wave form of the input to and of the output from the network. In Fig. 6, glowdischarge tubes each containing elements for two oscillators are used. The voltage transmitted by the coil L2 is adjustable by a resistance R15, and the resistances R6 are also made adjustable. Tuning of the note and its octaves is effected by adjusting condenser C<SP>11</SP>1. An instrument with an odd number of notes will leave one half Otr of a double glowdischarge tube spare ; this is utilized to provide a tremolo (controlled by a gradual switch Str in the grid lead), a sub-audio output at R16 varying the grid bias, and thereby the pitch, of the master oscillators. Fig. 7 (not shown) is a diagram of means for operating the instrument by A.C., including a rectifier-filter system, and a delay device protecting the master oscillators from a sudden application of anode potential. Fig. 8 indicates connections by which one keyboard may sound more than one stop-pitch, and by which two or more keyboards may be employed with one bank of generators. Each key actuates the two switches Sk, Sk of gradual contact type, one for the normal note and one for the octave above. Resistances R21 connected to the key switches adjust individual strengths and prevent robbing. 8 ft. and 4 ft. tones are collected separately, and taken (the lower tones through progressively more resistance) respectively to the leads 18, 19, Fig. 9. This Figure shows the tone-timbre system, operating by (1) out-of-phase octave combination, (2) filtering, to vary component strengths in certain ranges, (3) in-phase octave combination. A double vacuum tube (8) with a single cathode 22 and having the first plate 20 connected to the second grid 25 through a condenser C11 has 8 ft. oscillations led to grid 24, and 4 ft. oscillations led to grid 25. The 8 ft. oscillations become reversed in phase, and these out-of-phase oscillations combine at the grid 25 with the in-phase 4 ft. oscillations, so that the even-order harmonic components of the 8 ft. pitch are neutralized. The resulting oscillations with odd orders of harmonics predominating, and therefore of wood-wind type, are, at grid 25, out of phase with the oscillations in leads 18, 19, but become re-reversed in the second part of the tube so as to be in phase at the output 28. Actuation of the (gradalcontact) stop switches Sts in the various circuits shown utilizes the oscillations in the leads 18, 19, 28, singly or in combination, to produce the stop-timbres delivered at 35. In the Oboe, for instance, oscillations from lead 28 only are modified by a filter circuit C14, C15, R31 and resonating circuit L4, C16. The Open Diapason utilizes 8 ft. oscillations led through a filter R48, R49, R50, C27, C28, C29 and combined with 4 ft. Flute oscillations received by a branch 34. The general output at 35 from a keyboard is taken, with the outputs from other keyboards, to a two-stage amplifier through a condenser and through a resistance bridged across the amplifier and input; thence through a transformer and a low-impedance line with a constant impedance swell-pedal volume control, to a main amplifier and the loud speaker. Specification 477,653 also is referred to.