The Vocal Tractor is a strange sort of instrument that is an offshoot of my homemade Commodore 64 speech synthesizer. It uses the same SP0256 chip but in a manually controlled configuration. The SP0256 creates phonemes or partial speech sounds like those created by the human vocal tract (lungs, throat, vocal cords, mouth + tongue). Under computer control they can be strung together to form words. When manually controlled by a relatively slow human interface, these phonemes become textural, percussive, or drone type sounds. I built one prototype of this instrument which is now in the audio arsenal of the improvisational electronic musician Bonnie Jones.
The SP0256 chip uses a parallel input scheme to select from 64 phonemes and pauses. Because the input is binary, only six positions of 1 or 0 are needed to relay this data. So the prototype uses six pushbutton switches to create the binary input and a seventh button to "send" the data to the chip. Theoretically one could memorize the button combinations for each sound and create words by rapidly pressing the right buttons. In practice however, sounds tend to repeat or sustain before a new combination can be entered. Of course this allows the sounds to be used for entirely new effects.
The circuit is pretty much straight off of the datasheet for the chip. You can search for it at the Datasheet Archive - just be sure to type a zero between SP and 256, not a letter O. This version runs off of a 9 volt battery which does not last very long due to the 5 volt regulator wasting a lot of energy. I have some ideas for the next version including switches to preset a bit to 0 or 1 and a more ergonomic layout as well as power improvements.
To the Left are the six binary switches which are actually on the bottom of the unit in use. On the Right you can see the Send switch which can be pressed with the thumb. On/Off and a 1/4" audio jack are on the end of the unit. The screws secure the circuit board inside the unit and the silver plate covers a mis-drilled hole.
There is not really much additional circuitry to support the SP0256. A crystal to clock it, one transistor, some caps and resistors and an opamp to amplify the audio. It is perfectly happy wired up on perfboard with no critical component layout needed. There's still room on the board for some v2.0 improvements.
You can listen to two MP3 samples of me playing around with the prototype. The files are about 1MB each. Sample 1 and Sample 2