GB1162785A - Electronic Musical Keyboard Instruments - Google Patents

Abstract

1,162,785. Electronic organs. WURLITZER CO. 16 May, 1968 [18 May, 1967], No. 23389/68. Heading G5J. An electronic keyboard musical instrument has an electronic rhythm percussion accompaniment system which comprises a white noise generator 32 feeding amplifiers 62 and 30 through normally reverse-biased diodes 34, 38 and 50, and a brush keyer 46 which is arranged to cause the diodes 34 and 38 to conduct and a cymbal keyer 56 which is similarly arranged to cause diodes 34 and 50 to conduct when selected keys of the keyboard are depressed. The voltage pulse initiated by switching one of the key switches 24 is passed through stop switches 26, which operate the various percussion effects, and on to one of the keyers 46, 56 or 74 depending upon which stop switch has been operated. A pulse passing to the brush keyer is amplified and appears as a positive pulse at the junction 40 which switches diodes 34 and 38 on to allow a noise signal from generator 32 to be passed briefly to the amplifiers. The cymbal keyer is operated in a similar manner by switching the diodes 34 and 50 on except that the key switch in this case is operated by one of the foot pedals of the organ and can be held on as long as required. The drum keyer 74 is also operated by a foot pedal, the positive pulse from the drum keyer switching on a drum generator 70, the output of which is passed to the amplifying system. A shimmer generator 64 is provided to give a more realistic sound to the cymbal tone, by amplitude modulating the output from the generator 32 at a frequency slightly below the audio range. This is achieved by selecting the difference frequency of two adjacent tone generators 22 and passing this signal to junction 60. Detailed circuitry of the apparatus is shown in Figs. 3a and 3b (not shown). The noise generator comprises a transistor (192) used as a diode and biased to its Zener point to produce a noise voltage. The drum generator comprises a phase-shift oscillator which is biased short of oscillation and is switched on only by a positive pulse from the drum keyer. The output from the tone generators 22 is taken, after being switched by the key switches 24 to a pre-amplifier 28, and is combined with the output from the various percussion effects and fed to an amplifier 30 and loud-speaker 18.