Control circuit for sustain keyer circuit in electronic musical instrument

Claim 2

In an electronic musical instrument including sustain keyers each of which has a key-operated Switch operable to produce as audible tone signals and a capacitor for sustain-keying, the improvement in a sustain time control circuit, for and associated with each said sustain keyer, comprising: a switching element having a control electrode to be rendered conductive or non-conductive in accordance with a voltage applied thereto and connected to said capacitor in a time constant circuit in the sustain keyer circuit means for generating a rectangular wave signal at a frequency above audio levels having a variable duty factor controllable by an instrument player, and and means connecting said circuit means to said control electrode of the switching element for supplying thereto said rectangular wave signal.

Claim 3

A control circuit according to claim 1, in which said rectangular wave generating means comprises a triangular wave generating circuit, a Schmitt trigger circuit adapted to receive an output signal of a repetition frequency from said triangular wave generating circuit and to generate a rectangular wave, and means for varying a D.C. input potential to said Schmitt trigger circuit.

Claim 4

A control circuit according to claim 2, in which said means for varying the D.C. input potential comprises a variable resistor connected to said Schmitt trigger circuit for varying a D.C. input potential of the Schmitt trigger circuit.

Claim 5

An arrangement as in claim 1 wherein said switching element is a field-effect transistor.

Claim 6

A sustain keyer circuit comprising: a first field effect transistor having a gate electrode adapted to receive an input signal, a second field effect transistor having a gate electrode and being connected in series to said first transistor for establishing an output of said circuit, keying means for driving said first and second field effect transistors, a time constant determining circuit including a capacitor and a third field effect transistor having a gate electrode and further having a drain electrode which drain electrode is connected together with said capacitor to said gate electrode of said second field effect transistor, a Schmitt trigger circuit having an input and having an output connected to said gate electrode of said third field effect transistor for applying a rectangular wave thereto, a series circuit including a capacitor and a diode serially connected together and to the input of said Schmitt trigger circuit, a triangular wave generating circuit connected to said series circuit, and a variable resistance connected to said series circuit for varying the duty factor of said rectangular wave.

Claim 7

A sustain keyer circuit comprising: a first field effect transistor having a gate electrode adapted to receive an input signal, a second field effect transistor having a gate electrode and being connected in series to said first transistor for establishing an output of said circuit, keying means for driving said first and second field effect transistors, a time constant determining circuit including a capacitor and a third field effect transistor having a gate electrode and further having a drain electrode which drain electrode is connected together with said capacitor to said gate electrode of said second field effect transistor, a Schmitt trigger circuit having an input and having an output connected to said gate electrode of said third field effect transistor for applying a rectangular wave thereto, a series circuit including a capacitor and a diode serially connected together and to the input of said Schmitt trigger circuit, a triangular wave generating circuit connected to said series circuit, and a variable resistance connected to said series circuit for varying the duty factor of said rectangular wave.