DrumBox

This a collection of CR78, TR808 and TR909 based drum modules. I bought the PCBs and front panels from Analogue Solutions, but built them myself which gave me the opportunity to make a few feature enhancements along the way.

I have the following modules:

BD78 - CR78 Bass Drum
BD88 - TR808 Bass Drum
BD99 - TR909 Bass Drum
BD99 - TR909 Bass Drum (Yep, I've got 2 of these!)
SD78 - CR78 Snare Drum
SD88 - TR808 Snare Drum
SD99 - TR909 Snare Drum
CP88 - TR808 Hand Clap
RC88 - TR808 Rim Shot / Claves
HH88 - TR808 Hi-Hats
CB88 - TR808 Cowbell

Inside the box, behind the drum modules is a MIDI to drum trigger converter based on the Fat Controller design and PCB. Altogether the converter has 29 outputs as follows:

15 with velocity sensitive pulse amplitude (4V to 14V)
11 with trimmer set fixed pulse amplitude (4V to 14V)
3 with fixed pulse amplitude (5V)

This is the maximum number of outputs I could squeeze out of the Fat Controller PCB. The velocity sensitive outputs come from a multiplexed precision 14-bit DAC which is overkill really but I had one lying around - I didn't bother using precision opamps though! The trimmer set outputs come from an expansion board running from the connection that was used for the 8x2 ASCII display in the original Fat Controller design. And the 3 fixed amplitude outputs are 3 Fat Controller gate outputs.

As the CR78 doesn't have accents, the BD78 and SD78 circuits don't respond to different voltages, so they are hooked up to the fixed pulse amplitude outputs. The CB88 and one of the BD99s are triggered from the trimmer set outputs, leaving the BD88, other BD99, SD88, SD99, CP88, RC88 and HH88 (open and closed) which are triggered from the velocity sensitive outputs. The other 7 velocity sensitive outputs are connected via a D-socket on the back to trigger a modified TR606.

So I still have 9 trimmer set outputs and 1 fixed output left for future drum modules :)

The drum trigger converter only responds to MIDI Note On messages and gives a trigger pulse of a certain length. This length is set to 1ms on power up (about right to get a nice sound out of these Roland circuits), but the pulse length can be varied from 1ms up to 127ms by sending Polyphonic Aftertouch messages. For some of the drum circuits this gives an interesting variation in sound.

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