Roland TR-303 Schematics

The 303 filter is a diode-ladder filter (only that it uses transistors that
are
connected to act as diodes). So it is more similar to the EMS AKS or
Minisonic design than to the Moog in some way. It is a 4-pole filter; but
due to the pole location, which is quite different from Moog- or
CEM-filters,
it has more of a 18dB/Oct than the 24db/Oct slope in the interesting
range. (Of course, in the infinity, every 4-pole low pass is 24dB).

It is a 4-pole filter, with 3 poles the same and the 4th pole about 2.5
times higher in
frequency than the others. So, it will more resemble a 18dB/oct response.

https://www.timstinchcombe.co.uk/index.php?pge=diode2

https://electro-music.com/forum/topic-10441.html