Finally I had time to work on the VCO. I finished the second prototype and prepared docs for ordering a final prototype.
This is basic VCO because has only basic functions.
Triangle core with sync possibility based on the THAT2180 and OPA2604 chips. Regular TL07* opamp doesn't work here because of high wave amplitude. Limiting wave with diodes as were suggested gives problem with sync. So, only OPA2604 in the core.
VCO range is from 8 Hz to 14 kHz. VCO/LFO switch between timing capacitors. I used 100p and 10n 1% polystyrenes. So LFO range is 100 times slower than VCO.
No expo converter here because THAT2180 has expo responce. CV circuit is tempereture compensated with two 2K tempco resistors.
I used BCM847BC matched pair for sinewave circuit.
I used LM4040 precise voltage source for offset voltages to minimize pitch flow. I tested during 4 hours - pitch was stable in range +- one cent.
I installed Schmitt trigger on the sync input. So any wave is good for sync.
I was able to achieve cent-by-cent tracking as on the first prototype.
[video][/video]
The VCO - left board the core, right board - saw, sine, PWM circuits:
