GB371641A - Improvements in and relating to means for producing music electrically - Google Patents

Abstract

371,641. Electrical musical instruments. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. -(Assignees of Carlson, W. L. ; Kings Highway, Haddonfield, New Jersey, U.S.A.) May 21, 1931, No. 15051. Convention date, May 22, 1930. [Class 88 (ii).] Relates to the employment of two oscillators, each producing a fundamental and harmonics, of different frequencies so that a beat note is produced, with means for varying the pitch intensity and timbre of the beat note. Referring to the Figure, the two oscillators O, O<1> are tuned initially to the same radio frequency, and are connected through a potentiometer 18<1>, detector 19 and amplifiers 20, 21 to the loud-speaker 23. The oscillators have tuned circuits 4, 5 .. , 4<1>, 5<1> .. , respectively for their fundamentals and harmonics, coupled to them in parallel or series and connected to amplifiers A, A<1>. Short-circuits, comprising condensers 10, inductances 11 and variable resistances 12 under the control of spring- biased keys 24, and tuned to the fundamental and harmonics respectively of the oscillator O, control the amount of each component therefrom transmitted to the potentiometer 18<1>. A beat note of varying pitch is produced by varying the frequency of the oscillator O<1> by means of key-switches 17 in the circuits of condensers 14 of different capacity, the intensity of the fundamental and of each harmonic in the beat note being under the control of the keys 24. Oscillator frequencies sufficiently high are used to permit the required range of notes to be produced without overlapping of the components and without necessitating adjustment of the circuits 4<1> .., the action of the keys 24 thus being kept distinct. The leads 13 from oscillator O are connected across a portion only of the potentiometer 18<1> to prevent distortion ; or the generator O may be of smaller capacity than the generator O<1>. In Fig. 2 (not shown), the circuits of the fundamentals and of corresponding harmonics from the oscillators O, 01 are respectively connected together, under the control of keys 24, and are coupled to separate circuits each including an amplifier and detector, the output circuits of the detectors being connected to a single amplifier and loud-speaker. In Fig. 3 (not shown), the oscillators O, O<1> are each connected to an amplifying valve caused by negative grid-bias to operate on the curved part of its characteristic and thus to generate harmonics ; and the frequency of oscillator O<1> is varied by movement of the hand of the operator near a vertical electrode. Tuned circuits connected to suitable portions of the potentiometer carry the two fundamentals and the pairs of corresponding harmonics to separate circuits each including a radio-frequency amplifier with negative grid-bias, an audio amplifier, and a loud-speaker. The keys 24 are then arranged to control the grid-bias of the radio-frequency amplifiers.