Patent GB-1224396-A (GB)
Title: Improvements in or relating to keyboard electronic musical instruments
Inventor: TSUKAMOTO MASAO
IPC: G10H1/053
Filed: 1968-05-10
Abstract: 1,224,396. Electronic musical instruments. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 10 May, 1968 [12 May, 1967; 12 Oct., 1967 (4); 9 Nov., 1967 (2)], No. 22383/68. Heading G5J. General.-The invention relates to a keyboard electronic musical instrument which comprises a signal-selecting system 80 which is capable of selecting the tone signal corresponding either to the highest frequency or to the lowest frequency when a number of keys are depressed simultaneously. In the embodiment shown, one of the diodes 31 to 35 is rendered conductive when one or more of the key switches 21 to 25 are depressed, causing a signal from one of the tone generators 26 to 30 to pass to a common conductor 50 and on to the final stages 12 and 88 of the instrument. Stage 12 comprises a differentiating circuit 81, followed by a wave-shaping circuit 82 from which the signal is passed either to one 92 of a number of tone-forming circuits 85 and to one or more frequency dividing stages 83, 84 from each of which is taken an output to one of the tone-forming circuits 93, 94. The signal is passed from circuits 92, 93 and 94 to toneselector switches 95, 96 and 97 and on to a pedal switch 87 from which the signal is passed to amplifier 88 and loud-speaker 89. Signal selecting circuit.-The diodes 31 to 35 are normally reverse-biased owing to the arrangement of the bias resistors and the voltage source 58, but if one or more of the key switches 21 to 25 are closed only one of the diodes, either the one corresponding to the highest tone frequency or the one corresponding to the lowest tone frequency, depending upon the arrangement of the bias voltages, is rendered conductive. Decoupling capacitors 76 to 79 prevent coupling of the tone signal of any tone generator into the circuits of other tone generators. Capacitors 71 to 75 ensure the absence of noise pulses at conductor 50 due to switching. In an alternative embodiment (Fig. 3, not shown), several of the bias resistors are replaced by transformers, one for each note, Output circuits.-Fig. 4 (not shown) shows a circuit for stages 81 to 84, stage 82 comprising a four-stage transistor amplifier and speech clipper and stages 83 and 84 comprising emitter coupled multivibration to successively halve the frequency. Figs. 5, 6 and 7 (not shown) illustrate different embodiments of the circuit of stage 87, which comprises an amplitude control circuit which is triggered by an envelope control switched by the pedal 98. In Fig. 5, a battery is switched through a resistance/capacitance network to the trigger input of the amplitude control circuit to give an organ-like envelope, while Fig. 6 is a similar circuit in which a diode is utilized to give a piano-like envelope. In Fig. 7, movement of pedal 98 causes a shutter to move to allow a variation in the amount of light from a light source incident on a photo-resistor inserted in the lead between stages 86 and 88. Fig. 8 (not shown) illustrates a further embodiment in which the switching means 87 is connected between frequency dividers 83 and 84 and tone-forming circuits 92, 93 and 94. Complete instrument.-Figs. 10 and 11 (not shown) illustrate two embodiments of a musical instrument according to the invention. Fig. 10 shows an instrument equipped with melody keys and accompaniment keys in which the melody tone generators are connected directly to the key switches and on to a toneforming circuit to the output amplifier while the accompaniment generators are connected through a signal selecting circuit (see above) with its associate output circuits (see above) and on to the output amplifier. Fig. 11 shows an instrument in which both the melody and the accompaniment generators are connected to one of the said signal selecting circuits and on, through the said output circuitry to the output amplifier.