Keyer circuit for electronic musical instrument

Claim 1

In an electronic musical instrument, a sustain keyer circuit comprising: means establishing a circuit ground; a power source; an input terminal for receiving a tone signal to be keyed; an output terminal for deriving a keyed output; a first field effect transistor having a source electrode connected to said ground means, a gate electrode connected to said input terminal and a drain electrode connected to said output terminal; a resistor and a key-operated switch connected in series between said drain electrode and said power source line; a capacitor connected across said switch; a switching element having an inherent internal resistance and connected between said capacitor and said ground means; and a rectangular wave generator for generating a rectangular wave signal having a frequency above audible range and a duty factor variably controlled by the instrument player, said generator being connected to said switching element for rendering said element alternately conductive and nonconductive in response to said rectangular wave thereby exhibiting an average resistance, which resistance and gate and the capacitance of said capacitor cooperatively determining a decaying time constant of the circuit.