Synthesizer-controlled equivalent sound as produced tuneable VCOs which supply rectangular output One of four identical KOV (keyboard output fast opamp types ensures linear VCO operation well linearity of the voltage-frequency curve relevant to The outputs of buffer opamps Ar . . . A4 (ICI, Typerail grounded. The rectangular VCO output signal has a 50% duty factor; if not, adjust the relevant preset. As the four VCOs lack a linear to exponential KOV type. KOV signal whose frequency doubles.