well.... uh... it looks like i totally cocked up the ADC side of the flying squirrel circuit for the microphone! i must have been on drugs or something (someone slipped something into my hot water with a bit of milk). the connections i made to the LM13700 OTA bear absolutely no relation to the example schematics!
luckily i did manage to connect +ve and -ve to the right pins, meaning that the 3 LM13700s i now have are absolutely fine, so i've spent the day putting resistors on one of them like a porcupine, experimenting.
what's really awesome about the LM13700 is that it has a fascinating history of its own: http://www.idea2ic.com/LM13600/LM13700.html being an independent-buffered dual-version of an incredibly famous OTA - the CA3080 - which was first sold in *1969* http://www.till.com/blog/archives/2005/06/last_of_the_ota.html
i'm reminded of when i put the flying squirrel schematics in front of a chinese ODM for them to quote helping get it made, they said "that's a really old school design". i had no idea :)
anyway, i'm presently flipping quills on an LM13700 porcupine and also i'll errr... this time be actually... like... connecting the ADC VREF pins on the STM32F so that... y'know... the ADC actually works?
honestly... :)
l.