A while back I modified my Whippany Rhythm Master analog preset drum machine from the late 60's/early 70's. This normally sounds like your typical cheesy rhythm box to accompany organs from this time, but with a few mods you can open up some possibilities. There are no chips I messed with here, or no markings on the circuit board to give you. I pretty much just replaced some of the trim pots inside and some of the resistors with potentiometers mounted to a panel and fit inside a wooden case.
At some point, I will go back in and try to find the trigger points for the sounds. If I ever get the external triggering figured out, I will have a pretty bad ass analog drum module for less than $50. In the meantime, you can check out a video of how this sounds right now.