Keyer system for an electronic organ

Abstract

A keying system provides selectable decay times for individual frequency components of a tone to be generated by an electronic organ having a top octave generator producing a multiplicity of rectangular wave signals, and a plurality of associated divider circuits. The keying system comprises a keying block having a plurality of keyer sections. Each keyer section has a first keyer channel comprising at least two MOSFET transistors which are connected in series. At least one keying section further comprises a second keyer channel similar to the first keyer channel, a voltage threshold circuit which has a selectable threshold and switching circuitry to select output signals from either the first or second keyer channel of the one keying section. Each channel of the keying block is connected between a supply voltage and a load resistor which is in turn connected to a reference potential. Rectangular wave signals from the top octave generator and divider circuits are applied to the gates of a first transistor in all keyer channels of the keying block. Upon the depression of a key on a playing keyboard, a keyer envelope signal is directly applied to the gate of a second transistor of all first channels of all keyer sections; and the keyer envelope signal is applied to the gate of a second transistor of the second keyer channel of the one keyer section through the threshold circuit. The output signals from the first keyer channels are rectangular waves modulated by the keyer envelope signal. The output signals from the second channel of the one keyer section are rectangular waves modulated by the keyer envelope signal shifted by the threshold of the voltage threshold circuit. The modulated rectangular wave signals from the first channels of the keyer sections and the selected channel of the one keyer section are passed through filters and combined by output circuitry to sound the desired tones.