Can I expect a pure sine tone?

[Sotsirc]

When I listen to the sub oscillator in sine mode I hear really audible distortion (harmonics) even at low settings.
Should it be possible to get close to a pure sine tone?

[beefinator]

It's just how the oscillator is.  There's a little blip at the peak of the sine.

Just close the lowpass filter to cut out anything above the frequency of the sine, you won't lose anything of the desired waveform since it's just a sine.

If that's not enough, have the filter do 100% tracking and set the filter cutoff to always match the note being played, then turn up the resonance to boost the base sine tone in addition to filtering out higher components.

[Quinthius]

Actually I raised this question a while back as I noticed the sine wave was definitely not "pure", but was not sure if that was normal for analog synths or not.

Yves Usson very kindly investigated my question and gave a great explanation that the sine wave sub osc is actually not generated independently but is created from a mathematical formula applied to the saw or square wave (forget which).  I might be getting that slightly wrong but that was the basic idea.  So that is why those extra harmonics are in there.  It is more like a "pseudo-sine wave" since under the hood it has its origin in the saw/square wave (again, forget which).  He confirmed it is definitely not a clean sine wave - so that is normal, your unit is not defective - but at the same time it was not really intended to be used by itself, as its primary intention is to be used as sub oscillator underneath everything else going on, where you would not hear those extra harmonics so much.

So yeah... basically, you have to accept it as it is... a sine wave with character or use the tricks beefinator suggested (I prefer the first option, I like character!)