So, I kept playing with it and managed to make some headway - I’ve now limited the pitch drift to about the the last 10% of the duty cycle. Not perfect but certainly much better!
I stumbled across this thread: https://www.muffwiggler.com/forum/viewtopic.php?f=17&t=231130 and saw lots people repeating the problem (especially with the AS3340, like I’m using). I managed to treat the issue by including:
- 10uf electrolytic caps on the power rails
*100nf ceramic cap from pin 4 to ground
*changed the 10k resistor from pin 4 to ground to 56k (a la the datasheet)
*added a 100nf cap from pin 14 to ground - don’t ask me why
I also added a 1M resistor across legs 4 and 5 (something about hysteresis, means nothing to me) and it helped, but also reduced the pulse width pot to doing its full sweep in about 10 degrees of rotation. I cba to rectify that and it didn’t seem to make a huge difference, so away with it.
Thanks for the help everyone, I just want to rack this thing and play with it now, but alas it’s 2am on a Monday