Not too bad...just be careful to use only one VCO in square wave (that was what the TB-303 had) and only the lowpass setting on the VCF. Granted, the Neutron's VCF is 2-pole, not Roland's weird 3-pole LPF, but in the right parts of the range and with perhaps a tad of overdriving the filter, you should be right in the ballpark. Again, the sequencer is the key here...that odd non-linear glide that the original 303 has is another great example of a "wrong" design doing something "right", sort of like Moog's CP3 mixer.
-- Lugia
Thanks!
Although I think I have a solution, I'm still interested to know how experienced patchers would activate the CV control for the glide of the x0x heart module. For me, with the DAW doing the sequencing via MIDI, I would reach for a second MIDI channel just for the glide control, switching the glide on and off via "note on" and "note off" messages from the DAW that produce a gate output from a MIDI-to-CV module. (Another MIDI channel and MIDI-to-CV would handle the real notes.)
But I intuit that my first idea probably isn't the best one.