The TB 3k3 is my version of Oakley Sound Systems TB3030. I actually started working on this project prior to the Midibox SID, but being the more complex project out of the two it was completed only some 6 months after. Since I prefer playing keyboards, I decided to make a keyboard version instead of a rack module. As I don’t have a CV/Gate converter or anything else to drive the sound board with, the keyboard is a necessity in that sense too. No build photos of this project either so once again, the completed unit:
The casing is bent from a single sheet of aluminium 1mm thick as this is far easier to work with. Not that there was enough of it to make a bottom plate, so the casing remains well-ventilated until I happen to come across a suitable piece. Meanwhile, call it a easy access repairs or swift calibration adjustment model if you like ;) .. The wooden ends are nothing too stylish or expensive, just the average varnished b-grade birch I happened to have at hand. It won’t be too much of a task to upgrade them if I happen to get something fancier..
The keyboard was cut out from a damaged Casio SK-1 with the top part of it’s casing included. This allowed me to include the SK-1 speaker, should I wish to add some small 8ohm speaker amp at some point. The diode matrix of the keyboard is modified to a resistor network similar to the one instructed in Penfold Book. I built a separate circuit on a perfboard to create a gate signal from the keyboard CV, but I can’t recall whose schematic it is built from (will update this post when I locate it). Much to my amusement, there are a few things where this whole keyboard circuit fails rather big time.
First, as I didn’t have enough 47R resistors at hand to build the resistor network, I went for a slightly higher value. This of course results with the keyboard sending non-compliant CV per octave (0.8V to be exact, can’t be calibrated to a higher value). So either you tune the unit to be played with the keyboard OR by an external sequencer but not both. How handy.. d’oh! Safe to say, driving the synth with an external 1V/Oct sequencer but having it calibrated for the 0,8V/Oct scale, the results can be quite exciting for the fans of non-chromatic music ;)
Second, there’s absolutely no way of creating enough different control voltages from a keyboard to make the unit sound all-the-way-303ish. If played with the keyboard alone this synth is soundwise pretty far from a real 303 in action (I’m a big fan of slides and accent env mods) and you’re also stuck with tweaking a single knob at a time as the other hand is occupied playing a pattern. That said, the synth is still very neat for basslines but despite all my efforts, for any 303ish performances I’m still stuck with Rebirth. D’oh!