MXR-185 Drum Computer

YouTube via rolandsh1000

" Demo of my modified MXR-185 EPROM-based drum machine. A lot like the LinnDrum (I think it even weighs as much), but a bit kludgier: you can't change patterns on the fly, it seems to lock up when pattern data isn't defined as blank, et al. Still, I don't have the manual and I haven't dug too deep into the programming, so it might be much cooler (or much buggier?) than I'm aware.

The internal architecture is similar to the LInnDrum LM-2, in that it uses multiplexed clocks and also multiplexes the drum samples. The drum samples are mostly stored on 2732 eproms and seem to be linear (not companded though, like on the Linn). One lame thing is that the sounds are stored on the EPROMs in a scrambled fashion, such that the addressing is not linear. This is a problem because you have to know the scrambling order to make your own EPROMs (though I think the Oberheim PROMMER can burn them). The toms and the open hat have VCA enveloping (using CA3280s). The shuffle is really stiff, though - the microprocessor cyclically drives the control voltage of a master 555 clock and it doesn't sound great at all.

I modified this one with the same tuning circuits I used for the LinnDrum LM-2. The only one I couldn't get to work was the crash cymbal. I also added pots that modify the control currents that go to the OTA's that VCA the toms and open hat, so that allows you to change the decay of those samples.

Overall, the sounds are pretty punchy, though, and I think sonically it could compete with other similar EPROM based machines."