Circuit bending a SK-1 is a rite of passage for electronic musicians and electronic tinkerers, and something I have always wanted to do but until recently never had the time or know how. Months ago I came across a dead SK-1 on ebay for under $20 (including shipping) and managed to locate and replace the burnt transistor preventing it from powering on, which was an amazing feat considering I know almost to nothing about electronics. There were a couple other things wrong with the keyboard, but it generated sound and that's all that mattered. After all, circuit bending is essentially breaking a device in a controlled manner.
The SK-1 is probably the most bent keyboard on the planet and thankfully there are plenty of people who share their bending experiences on the Internet. After weeks of research I was able to learn enough about the device to feel comfortable attempting some mods. I had a very specific goal in mind.
I've listened to many samples of bent SK-1's and noticed they mostly make crazy sound effects and are not very musical. I wanted something more practical, something I could rock out with. Pitch bending was a must and sounds had to be quickly recallable. Below is a list of popular bends I used, then I added a twist of my own:
- Syncro's anti-aliasing filter bypass (crisp!)
- Reed Ghazala's Aleatron pitch bend with body contact for vibrato
- LTC1799 pitch bend and speaker-to-line out mod from circuitbenders.co.uk*
Probably the single most popular Casio SK-1 bend involves adding a patch bay and hooking it up to the ROM/RAM chips, similar to the Tablebeast mod. While there are thousands of connection possibilities on the keyboard's PCB, I found that most of the interesting and practical sounds came from simply hooking one side of the ROM chip to the other. So rather than install a messy patch bay I wired each side to a single-pole, twelve throw switch. While there are hundreds of possible combinations per patch most of these either crash the machine, do nothing, or make redundant glitch noise. My creation provides only a few new, practical sounds, but they great and can be called up instantly by dialing in the two rotary switches.
One unexpected bonus is that the bending process caused the keyboard to play notes a 4th lower than normal, which is great because I think the SK-1 is more useful in the lower ranges.
The final construction of the VH-1 keytar involved cutting out a section of the chassis with a rotary tool, then running the wires through a pair of 3/4" PVC pipes bound together with athletic tape into a project enclosure housing the switches and potentiometers.
All of the SK-1's original functionality is still there and can be used as a stock keyboard, except for the built-in microphone which was broken when I got it (the line in still works).
*Note: The LTC1799 bend is also featured on GetLoFi and greightbit's Instructables tutorial. (WARNING! Do not use the wiring diagram on the Instructables site, use greightbit's video instead. The drawing is wrong at the time of this writing and will fry your LTC1799 clock. Guess how I know this?)