Patent GB-1133208-A (GB)
Title: Electronic musical instruments
Inventor: DUNLOP JOHN HENDERSON
IPC: G10H1/22
Filed: 1965-12-09
Abstract: 1,133,208. Electronic musical instruments. WURLITZER CO. 9 Dec., 1965, No. 52367/65. Heading G5J. [Also in Divisions H1 and H3] An electronic musical instrument having a keyboard with keys and corresponding key switches, e.g. an electronic organ, and in which a note once played is sustained, includes a switching circuit which allows a note to be sounded upon depression of a given key and which simultaneously acts to cut off the sustain of any previously sounded note to prevent the production of beats which would otherwise occur between notes, particularly bass notes, sounded together. Preferably capacitors are used to sustain the note played. The switching circuit includes a series of separate circuit paths connected to a common output, along each path of which a signal corresponding to a particular note to be played is conducted, each path including a diode 98, an electronic switch 84, e.g. a neon discharge tube, and a sustain capacitor 86. As shown in the Figure bass notes are sounded by operation of a pedal which closes corresponding contacts 48, 50 and 52 on to busbars 34, 36 and 38 respectively; the other contacts 48 remaining in contact with bus-bar 32. Contact 48 operates to apply a negative D.C. potential which fires neon discharge tube 84 to render diode 98 conductive. At the same time capacitor 86 charges rapidly. The diode connects the output of a treble oscillator with a frequency divider, Fig. 4 (not shown), to produce the bass note which is fed into an output circuit that is opened by a potential derived from contact 52 and bus-bar 38. Any charge remaining in a capacitor corresponding to a previously sounded note is dissipated by a positive D.C. potential applied to bus-bar 32 and the contacts 48 still connected to it when contact 50 is closed on to bus-bar 36 so that all the diodes, except the one corresponding to the newly sounded note, are reverse biased and rendered non-conductive. The firing of gas discharge tubes in series is avoided by arranging that contacts 48 break after contacts 50, 52 when the pedal is released so that the capacitors of the undepressed note circuits have time to discharge their positive charge to an extent sufficient to prevent series discharge before contact 48 is broken. A second set of handoperated keys and keyswitches housed separately in the chord unit of the organ, Fig. 5 (not shown), may be provided in addition to thepedals and without duplication of parts other than the actual switches, so that the bass notes can be played by hand. These auxiliary switches are connected in series with the pedal switches across the appropriate points X-X above resistances 82. The arrangement is such that when no auxiliary bass note key is depressed the pedal key switch circuit is connected to resistance 82, but when an auxiliary bass note key is depressed the corresponding pedal key is disconnected so that the positive potential which is applied to all the remaining undepressed circuits via busbar 32 does not render the depressed circuit inoperable by cancelling the negative pulse. The main difference between the auxiliary and pedal switches is that the auxiliary switches are individual switches which comprise a plurality of contacts ganged together by a wire, rather than being a continuous bus-bar. Construction of the bass pedal contacts is described, Fig. 1 (not shown).