GB975627A - Improvements in electronic organs - Google Patents

Abstract

975,627. Electrophonic musical instruments. WURLITZER CO. July 8, 1963, No. 26949/63. Heading G5J. [Also in Division H3] A tone-producing system for an electronic musical instrument comprises a plurality of audiofrequency generators producing complex electrical oscillations connected in groups of sequential semi-tones to band-pass tone filters each consisting of interconnected inductance and capacitance elements tuned to pass the fundamentals and discriminate against the harmonics of the group of generators to which it is connected, each filter having at least two inductances and being overcoupled to have a double-peaked response curve with the frequency range between the peaks substantially equal to the frequency span of the fundamentals of the group of generators. As shown in Fig. 1 forty eight tone generators 10 are divided into eight groups comprising a half-octave of semitones and connected through switches 12 to junctions 14. Junctions 14 are connected through capacitors 16 to a common bus 18 and in the sixnote groups through capacitors 20 to eight busses 22 which are connected to contacts 24. Contacts 24 are engaged by a common movable switch arm 28 which is shown schematically as a plurality of ganged arms. Switches 28 are grounded and comprise a flute stop. Switch contacts 24 are connected through resistors 30 to filters 32, there being eight such filters all connected to a common bus 34, amplifier 36 and loudspeaker 38. Common bus 18 is connected to a fixed switch contact 42 of an oboe stop and to a fixed switch contact 44 of a trumpet stop. The oboe stop includes a movable switch arm 46 which is grounded in its rest position and is shunted to ground by a resistor 50, connected to filter F1 through resistor 52 and to filter F3 through resistor 54. Similarly the movable switch arm 56 of the trumpet stop is connected to filter F2 through resistor 62 and the to filter F4 through resistor 64. All the filters 32 are of the same configuration although the values of the electrical components differ. Each filter comprises inductances 88, 92, 106 and capacitors 100, 104, the inductive coupling being through the inductance 106. The filter response curve (Fig. 4, not shown) is a double peaked curve, the frequency range between the two peaks being the frequency range of the fundamentals of the six notes fed into any filter. The response curve has a sharp upper cut-off, thus eliminating the second harmonic and all higher frequencies, and a relatively less sharp lower cutoff which cuts down the fundamentals of notes falling below the first peak but allows some of the harmonics to pass through. The Specification includes modifications of the filters (Figs. 5 and 6 not shown).