Yay! Good to know there is another fan here - they really are superb hey!
It took me a little while to fully understand them, but now I absolutely rate the Hertz Donut mkII as one of the best complex oscillators out there!
My tips to get the most from it as a new user:
Turn all attenuverters to their centre position, Discontinuity, Tracking (off) and Modulation to zero, choose Sine waveforms for both oscillators and just patch the main Sine out to the mixer.
Really important: Tune the oscillators to each other < seriously, take your time here, they are super sensitive, but your experience will be transformed if you get it right!
Then turn on the through-zero FM and slowly bring up the Modulation knob to discover lovely FM bell tones!
Once you have found this you have found the most pure of Hertz Donut sounds, from there just adding a tiny bit of any of the 3 flavours of Discontinuity wave folding will give you endless timbres, after that, well, just experiment... remember less is more, but sure... why not go all out and turn it all into a snarling cacophony of sound!!
Pro Tip: use Argos Bleak to generate the ratios ad intervals for your oscillators in FM mode - prepare to be amazed!
I am taking commissions for synth builds. UK ONLY for now. DM for details :)
You can find my modular synth album here https://kel-audio.bandcamp.com