Hello all! I don't currently have access to my build, but I'll try to post a video later today. The low, raspy sound is gone, the sound is much cleaner, and the frequency now smoothly transitions to the zero beat through the lower octaves.
What I did, in chronological order:
1. Added JFET follower stages (did not seem to have a big impact)
2. Previously had both oscillators power and ground rails directly connected; disconnected them and added a small RC filter at the connection between each and the +12V/GND rails (I think this had a small effect, but there was still locking)
3. Physically moved the oscillators about a breadboard's length apart (this fixed the locking entirely)
I also had a small issue where my JFET followers seemed to "drift" from a full 400mVpp amplitude to practically zero. Do not make the same mistake as me... the gate on your JFET needs a resistor to ground (which seems very obvious in retrospect, but it was a big system!)
I was not really expecting physical distance to have such a big effect on the inductor interactions (something something inverse square law). I kind of thought people were exaggerating the effect, but no, it's like 400Hz minimum frequency down to like 20Hz.
ILYA, this is my exact shopping list:
- 10mH inductors: https://www.digikey.com/en/products/detail/epcos-tdk-electronics/B82144B1106J000/3501400
- 1mH inductors: https://www.digikey.com/en/products/detail/bourns-inc/RL181S-102J-RC/946948
- Capacitors and resistors I just took whatever I found, seems to work fairly well
