Quantisise VCO


Here is a wide range, non-precision, and somewhat unstable voltage-controlled oscillator (VCO) with just a pot for initial frequency, a CV input attenuator, a triangle (-0.5 to +4.5 volts) and a square wave (+/-14.3 volts).  It uses an obsolete part (CA3080).  Perfect for the Quantisise!

This CGS SSG board is built as a dual VCO for the Quantisise, which uses three of these boards.  The Serge SSG consists of two virtually identical voltage-controlled slewing circuits that, depending on how patched, can function as a straight-through slew, an LFO/VCO, or a Sample & Hold.  I also used this board in the CGS-Serge panel to make a true SSG.  Here, the two circuits are each hard-wired to cycle as a VCO.  This schematic shows one of the circuits, as built, plus a bit of wiring for an unused section of the LM3900.  (Ignore the LED driver.)

There’s no external input.  The parts for the one-shot circuits and the hold inputs are omitted.  A jumper from pin 5 of the cycle comparator back to the input (A, K) patches the feedback that makes it oscillate.  I’m using the same 47 nf capacitor as I used in the Quantisise S&H as the integrator.  This gives a maximum frequency in the 3.5 Khz range.  The low end is as low as you need, virtually stopping.  Much of this range can be swept by a 5-volt CV.  The Cycle Out will be patched to a One Shot input on a S&H board and optionally routed to S&H Hold inputs by toggle switches on the Quantisise control panel.



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