I’ve created a VCO design based on the LMNC 1222 design but without the tuner and adding in a sine wave generator and a 6 octave selector. I thought I’d build it out on a breadboard first before designing a pcb for this but I’ve hit a problem… it’s going really slowly about 1Hz!
I think it’s something to do with the FM input, I noticed if I remove C13 and leave R22 disconnected from ground it goes at the sort of speed I’d expect but with the floating connection it’s very noisy. If I then connect R22 directly to ground I get no oscillation at all! I’ve also tried changing out C13 to be 10nF and 0.1nF but no change happens.
Nb. I’ve not implemented the sine wave generator portion as I need the triangle working first so I guess you can ignore that bit!
Any suggestions on why this is happening are super welcome… I’ve attached the schematic to see if anyone can spot something dumb I’ve done here!
I tried another I had and it all started to behave!! Note, now that I have things working I’ve updated the PWM input to give a full sweep and I’ve decoupled the Thomas Henry based wave shaper to center on ground so I don’t get something like the MacArches coming out!