Selective keyer biasing to enhance percussion effect

Abstract

A keying system provides selectable decay times for individual 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 keyer block having a plurality of identical keying sections. Each keying section comprises at least two MOSFET transistors which are connected in series and the series combination is connected between a supply voltage and a load resistor. A multiple position switch is connected to each load resistor to selectively connect the load resistor to one of a plurality of biasing voltage supplies. Rectangular wave signals from the top octave generator and divider circuits are applied to the gate of one of the transistors in each of the identical keying sections of the keyer block. Upon the depression of a key on a playing keyboard, a keyer envelope signal is applied to the gates of the other transistors in each of the identical keying sections of a keyer block. Upon receipt of the rectangular wave signal and the envelope signal the keying section provides an output signal which is a rectangular wave form that is modulated to varying degrees by the keyer envelope signal, the degree of modulation depending on the biasing voltage applied through the multiple position switch to the individual load resistor. The modulated rectangular wave output signals from the individual keying sections are passed through filters and combined by output circuitry to form the desired tones.