After a number of important revisions, the very first reliable, stable and interesting VCO is finished! Some features:
– Instead of a classic configuration where the sawtooth core is reset by a voltage comparator and a small capacitor, this sawtooth core is reset by a Schmitt trigger configuration, allowing LFO functionality by switching on an extra capacitor in the sawtooth core. This because the reset pulse does not rely on the size of the reset-capacitor but is determined by the Schmitt trigger.
– Double reset transistors over the same capacitor(s), one for the Schmitt trigger saw and one for the hard-sync in.
– Cheap, almost all components are easily available. The total cost of the base-board (without jacks, pots and PCB) is €6,-.
– Outputs: Saw, Ramp, Triangle and PWM. Multiple voltage inputs, of which a number are attenuated. PWM settable via input or direct via potentiometer.
– Base-board can be used without top-board in e.g. polyphonic configuration.
– Most resistors and capcitors are smd, saving PCB space but not having influence on the raw, gritty sound.
– Routed by hand ;)
Following is a link to a demo on YouTube where I’m learning to use 3 of these VCO’s together, the schematics in PDF and the schematics and board design in Eagle format.
VCO topview which shows the correction on the hard-sync input. Further SINE and LINFM were discarted. So, the topboard will need a revision ;)
All 3 VCO in perspective view. Switches are added to switch between VCO and LFO functionality.