Schematics / A 440 Oscillator Version X
A440 Oscillator Version X by Henry ,visit his page Henry's Exciting Circuits for details on this Test oscillator and more http://homepage.ntlworld.com/henry01/henrys_exciting_electronics_contents.htm . From there the brief description :
While tuning my Oakley and other homer VCO synth modules I originally used to use and old £45 Maplin "Precision Gold" multimeter of 1990 vintage and use the surprisingly accurate frequency counter on there to set the VCOs to the A440 international tuning standard. However I'd seen a prototype Moog module in the booklet of the Switched On Bach CD box set which Bob Moog once made as a Christmas Present for Wendy Carlos. I thought it was time for a crystal controlled reference oscillator design. The requirements were standard crystal stability (easily good enough for analogue synths), sine wave output and extreme simplicity and cheapness.