Over the years, I have stated my approach of modeling to this community but I will reiterate it for new members. When doing a model, my first step it to create an over detailed simulation model in order to try to capture the sound of the original as close as mathematically possible. Once I have that over detailed model, I start making optimizations by removing the parts that are complex and have little impact to de sound. The next step is to play with the model or my custom circuit in order to personalize or “fix” quirks of the original, basically modding the thing. Last step is to create the DSP code.
In the case of the drums, the careful looker will see that these are not exact 909 drums, starting with the fact that these have more controls than the original 909 drums. These are my modded circuits. I always avoid using the word “emulation” because that’s implies that if you get a 909 and you compare the sound of mine it must sound exactly the same. But that will never be the case. Even my two snare boards that are made with the same components sound different. This is in part due to the tolerances of the components and the differences in the semiconductors. I have some measurements that I will publish at some point.
In conclusion, if you would like to have a version of the drum machine that I would have made in the 80’s, this is it. The analog drums are based on the 909 circuits but they are modded versions (check specially my Rim and Toms). The cymbals are custom and the 808 kick is modded as well.