I am using a single 74HC14 (hex schmitt trigger) to implement three oscillators. I now have a test build ready and encounter problems. See schematic, it shows component values. Also
- proper 5V power supply
- 2u2 electrolytic bypass near chip
- 100n ceramic disc bypass next to chip
- unused schmitt triggers' inputs are on ground or vcc
- outputs connected to inverting opamp amplifiers, each their own opamp with 100k and 500nF in series to the inverting input (the C is for DC blocking)
The problem is: each of the three oscillators interfere with the other ones, changing their frequency. E.g. if oscillator 1 is set at 50 Hz, turning up 2 or 3 will cause 1 to go up in frequency (wild changes, think +50%)
I'd think the schmitt triggers are not loaded very high (resistances are all >100k, problems occur with the potmeters at around 200k already) so surely I'm not pushing it in terms of sink/source current.