Analog Wavefolder for adding harmonically related overtones
Farbfolder is an analog wavefolder for Eurorack. It does this weird and wonderful trick of folding the wave at the zero points, "squaring" a sine off with more and more sinusoid edges, thus adding odd harmonics.
https://makingsoundmachines.com/farbfilter/
Available as an assembled Module and as a DIY project.
This Module is currently available.
$110