Patent GB-757984-A (GB)
Title: Improvements in and relating to organs
IPC: G10H5/10
Filed: 1953-04-20
Abstract: 757,984. Electrophone organs. CUTTERIDGE, O. P. D., HONESS, B., ROOPE, J. W. T., and WEST, R. L. April 13, 1954 [April 20, 1953], No. 10805/53. Class 88(2) A monophonic electrophonic unit comprises an electronic oscillator housed in or connected to a pedal box 10, Figs. 5, 7 (Prov.). The oscillator 13 is controlled by the pedals and generates a substantially pure sine wave which is shaped in stage 14 under the control of stops on a board 15. The shaped oscillations are fed through an amplifier 16 and leads 17 to a loudspeaker. Power is supplied from a unit 18. The oscillator comprises two triodes 51, 52, Fig. 1, the latter being arranged as a cathode follower driven by the anode of 51. Feedback over a parallel-T-resistance-capacity network X, an example of which is shown in Fig. 8 (Prov.), sustain the oscillations. The network X may include a non-linear resistance 26. A positive feedback provided by a, connection 56 between the cathode circuits of 51, 52 serves as a gain control and as a fine frequency control. The pedals, in effect, control the condenser 24 and the resistance 25 in X to change the frequency. Each pedal, when pressed, connects an individual resistance and a condenser common to a group of pedals. The wave shaper comprises a triode 37, Fig. 10 (Prov.) in the grid circuit of which, a resistance controlled by stops 41 determines the amplitude of the oscillation applied to the grid and hence the extent of overloading. The resistances 40 may be replaced by networks including non-linear elements. A switch construction actuated by a pedal 12 is shown in Fig. 6 (Prov.). The pedal is pivoted at 35 and is biased by a spring 36. The pedal is connected to a spring strip 29 by an adjustable link 28 so that on depression of the pedal, a depending lug of the spring strip engages a spring lug 33 and completes a number of electrical circuits, one of which includes resistance 25, Fig. 8 (Prov.). A circuit for controlling attack comprises a cathode followed 56, Fig. 2, followed by a triode 57 providing the output. A diode 59 acquires a positive cathode potential when it conducts in the presence of a signal and condenser 62 is charged through a delay circuit including resistors 61, 63. Triode 57, which is normally biased to cut-off is not enabled until the condenser 62 has charged sufficiently. Diode 64 prevents the grid of triode 57 from becoming positive with respect to the cathode and diode 65 discharges condenser 62 at the end of a signal. The Provisional Specification describes means for providing different musical effects from small reed organs, pipe organs, piano-accordions or harmonicas. A number of microphones 2, Fig. 1 (Prov.) are situated within a sound-proof reed chamber of a small organ and are connected in parallel to common leads. The microphones are mounted so that their diaphragms are not parallel to any flat rigid surface and some of them are connected in reverse so as to minimise the effects of vibration. Groups of microphones are connected to pre-amplifiers 4, a volume control 5, a mixer 6, an amplifier 7 and a loudspeaker 8. Different groups of microphones may be acoustically damped or loaded. Tremolo is produced by a circular disc 43, Fig. 11 (Prov.) rotated about its diameter in front of the loudspeaker. The disc is driven by an electric motor 46 and is normally unbalanced by a fixed weight 48 and a spring-biased weight 49 so that, when at rest, the disc does not obstruct the loudspeaker opening.