LZX Industries CADET VCO
The XR2206 gave poor results at high frequencies with reduced amplitude and noises. The trimmers were a bit of a pain to set as well. I was not very pleased with the result. I decided to use the open-source Lzx industries cadet vco . I made a PCB with 0805 smd componements and through-hole transistors for matching them (boring). I added to the circuit inverted outputs for both original outputs (square and triangle). The LM6172 were quite sensitive to what seems to be the ringing of the 74HC14 and produce noise at 42MHZ. A 10pf cap in the feedback loop solved the issue. A test jig was made for testing two vco and observe the modulation between them. I used the video extractor to provide proper syncs and video signal for modulation. It gave great visuals and patterns, alhough black and white (no video encoder). The vco can be modulated by video signal as well (picture 3 and 4) which give me the idea of a potential video extractor to modulate the VCOs.