Envelope circuit for a keyboard type electronic musical instrument

Claim 1

In a keyboard type of electronic musical instrument, a plurality of envelope circuits having a damping and sustain characteristic and each comprising a keyswitch operated in association with the actuation of a key on the keyboard of the electronic musical instrument, a power supply, a voltage responsive circuit coupled to said power supply for producing an output tone, the volume of which decreases as the magnitude of the voltage applied thereto decreases, a sustain circuit means coupled to said voltage responsive circuit for causing the operation of said voltage responsive circuit to continue, a time constant circuit means having a first resistance having a first terminal connected to said keyswitch and a second terminal and a first capacitance having a first terminal connected to the first terminal of said first resistance and to said keyswitch and a second terminal connected to the second terminal of said first resistance, said first capacitance being coupled to said power supply in the normal position of said keyswitch for being charged thereby and being coupled to said voltage responsive circuit when said keyswitch is in the other position with the key actuated for delivering a decreasing voltage to said voltage responsive circuit, the initial magnitude of which is proportional to the time which said keyswitch takes to move from the normal position to the other position, a second resistance connected between the junction of the second terminals of said first resistance and said first capacitance and said sustain circuit means in series with said first resistance for providing a voltage to said sustain circuit means when said keyswitch moves away from said other position toward said normal position when the key is released for causing said sustain circuit means to deenergize said voltage responsive circuit, third resistance connected between the junction of the second terminals of said first resistance and said first capacitance and ground, a single sustain switch for all said envelope circuits connected in parallel to said sustain circuit means in each envelope circuit for bypassing said voltage supplied to said sustain circuit means from said time constant circuit when said sustain switch means is closed for making said sustain circuit means inoperative to deenergize said voltage responsive circuit, and reverse current flow preventing means for each sustain circuit means connected between the sustain circuit means and said sustain switch for preventing reverse current flow from individual sustain circuit means into other sustain circuit means, whereby said voltage responsive circuit continues to produce an output tone.