Video showing the settings for my version of the clarinet sound.
Two oscillators are needed for the clarinet patch to sound alright: one is a square wave, the other a sawtooth wave. The tricky part is to find the right balance between the filter cutoff frequency (low-pass filter) and the amount of filter cutoff envelope. Well, at least, that's what surfaced from my fiddling around.
The envelope is mostly sustain with a tiny bit of attack and release.
Patch wise, there's a little bit of vibrato, in other words, the pitch is modulated by the Low Frequency Oscillator (LFO) with a triangle wave. Although not necessary, I have added a little bit of amplitude by having the envelope generator (EG) modulate the amplifier (VCA).