(Update - This is the second version of the XR80 Drum Kit, I had previously edited the ADSR envelope controls within the envelope control area, where I think I should instead be attempting to control as much as I can via mathematical expressions. The filters are still external to the expressions.)
This is my second attempt at a drum kit using mathematical expressions in Xpressive. Again, it is inspired by the analogue Roland TR-808. This time, I referenced to the TR-808 Service Manual, specifically the section describing the sound generator circuits. I do need to spend more work and check / get the tones right. I only have a close clone at home (Behringer RD-8), so when / if I do further work here, I will compare tones and timbre to samples to be sure. I wished to put this here copyright free in case anyone wants to use it / improve it / study it / make their own drums, as it may take some time until I come back to it as I am on to another idea.
I also started the same with the TR-909, but as some of the drums in the 909 are 6 bit samples, I decided that I may as well continue to use samples for the 909.