Here it is, with the said changes.
303v5pJ.axp (50.2 KB)
At the moment I have no clue what to do with the filter. I have done some reading on resonant filters and they seem to work by having a feedback loop which introduces the peak at the cutoff frequency. I think (I may be wrong) the 303 has a HPF in this loop and this is what makes the bass disappear when the resonance is increased. I don't know how to emulate that with the objects we have.
I think the sequencer is the best bit of this patch. Everything else is nominally right (or at least in the right direction) but if it is to be closer to the authentic sound, work needs to be done on the oscillators, filter and the FEG.
After reading some of the thread alex linked I made a quick version of the square osc (from how I understood what antto wrote in there) using two phasor saw waves, one of them inverted, which were then summed and put through a high pass filter, and the result looks more like the 303 square than before. The filter, like I said, I don't know what to do about it. The FEG has to be bipolar so that increasing the depth also makes it go lower on the decay but I don't know how to build this, though I suspect it can be done with some thinking.
I'm pretty proud of this patch anyway, it sounds wack in it's own right. Especially the filter tracking across a sequence that has notes from a few octaves is nice and can lead to unpredictable results. I was hoping to make it a support for my x0xb0x since I can't afford another one and I guess it is usable for that as it is. It's a different flavor but pretty acid.