Patent GB-494759-A (GB)
Title: Improvements in or relating to electrical musical instruments
IPC: G10H3/08
Filed: 1937-03-25
Abstract: 494,759. Electrical musical instruments. COMPTON ORGAN CO., Ltd., J., and BOURN, L. E. A. March 25, 1937, No. 8862. [Class 88 (ii)] Relates to tone generators in electrical musical instruments in which an audio frequency voltage is generated electromagnetically or by resistance variation by a direct exciting current which determines the amplitude of the voltage, and consists in the provision of capacitative means to make gradual the build-up and/or decay of the direct current whereby a gradual attack and/or die-away of the tone results. In Fig. 1 a single tone pitch is generated by a phonic wheel 3 in a coil 1 on a core 2 polarized by a coil 7 which is connected through a resistance 6 to a current source 5 on closure of a key contact 4a. A large capacity condenser 8 in shunt to coil 7 charges gradually, causing gradual polarization of core 2 and gradual attack ; it discharges through the coil 7 giving gradual die-away. With the condenser at 9 instead of 8, instantaneous attack with longer die-away is produced. Condensers at 8 and 9 may be used simultaneously, and another resistance may be inserted between 6 and 7. Condensers and resistances may be variable. In Fig. 2 (not shown) the generator comprises a selenium cell in series with a resistance and modulated by undulating light, with a condenser filtering out the direct current component in the output circuit. Fig. 3 (not shown) shows the arrangement of the circuits (which may have different attack and die-away effects) for the partials of one note. Fig. 4 shows means for the preventing of robbing in borrowing both on the same and on different manuals. The generator 7 is required as a partial for the key contacts 4b<1>, 4b<2> of different notes on one manual, and for key contacts 4b3, 4b<4> of notes on another manual. Simultaneous closure of a number of these contacts on to the partial bus-bars 15 ... 18 gives increased energization of coil 7 through resistances r<1> .... r<4> in parallel. Each stop closes a set of contacts s<1> ... s<4> on to the partial bus-bars of its manual, and simultaneous closure on one bus-bar (15) of contacts pertaining to a number of stops (s<1>, s<2>) likewise increases energization of coil 7, through resistances (r<5>, r<6>) in parallel. Earthed resistances r<15> ... r<18> stabilize the bus-bar voltages, and resistances r<19>, r<20> preserve adequate volume variation with only a few stops in use. Additive effects may also be obtained by providing separate coils 7, Fig. 1, for each copitch partial of different notes, wound either on the same core or on different cores having a common phonic wheel. Swell pedals operating by current controls r<13>, r<14>, or by varying the reluctance of the magnetic systems, are provided. Pitch-wobble tremulants, operating by oscillating the cores 2 or by varying the rotation of the wheels 3, may be added. Intensity tremulants, operating by volume control on the amplifier, groups of coils 1, or the polarizing supply, or by variation of the distance between the cores 2 and wheels 3, may also be added. Specifications 388,036, 494,758, 403,444, and 433,050 are referred to.