I’ve gotten several requests on how to hook up the Casio Sk-1 with a Getlofi1799 Oscillator so I’ve quickly drawn up a diagram for hookups. According to other sources the clock input can be directly injected without cutting the trace. That may be possible but there are bootup problems if the clock isn’t at it’s original setting so you may need to add a switch regardless. The note about the optional 500 ohm resistor is only if you notice your sk-1 is now out of tune for wiring to the clock lines. this should drop pitch to a range where you can fine tune the keyboard back to A=440. Access to the fine tuning is available thru the bottom plate of the sk-1. Click thru on the pictures to get an exploded view of the diagram.
Here is a link that Roger sent me a while ago. Its a website by Frans Samshuijzen with detailed descriptions of some mods that he did to a set of Casio SK-1 keyboards appropriately titled: “Casio Twins“. The mods include a full pitch mod with the use of a TI 74LS624 voltage controlled oscillator. It is also worth noting that a 555 timer circuit would theoretically do the same thing, except that the max frequency of a 555 is about 2Mhz and with the LS624 chip the schematics indicate a range of between 1.5 and 10Mhz with a max of 20Mhz. The downside however is the fact that the LS624 is far more expensive, $2.55 a pop. Still worth every penny considering that the Casio will provide for a full 3 Octave mind melting sound experience, along with longer and grainier recording times. Other mods include a nice line level adapter schematic for the microphone input and a remote trigger option. Audio of the improvisations on the Casio Twin set can be heard here and there is more information about what all the controls are here.
Gijs of Geiskes.nl has just sent me some information on their recent experiments with patching signals from an Casio SK-1’s ROM chip to a video monitor. The circuit is simply a diode to prevent the back flow of current and a resistor to drop the +5 Volt logic gate to a +2 Volt required for generating a video signal. The color of the pixel is determined by the voltage in between 0 ( Black ) and 2 ( White ), so if multiple points on the ROM chip were mixed with various resistor values color images will occur. Gijs’ result is a series of lines that appear on a monitor in a scrolling fashion. The resulting image is neat and in sync with the sounds generated, however it is out of sync with the screen. The NTSC and PAL video standards require a sync pulse to be sent every so often, without it the image will scroll. Very nice work and I am sure that this technique will work with other circuit bent devices.
Video on of the bend is on YouTube.
There is nothing quite as mesmerizing as watching the patch arm of this mechanical-electric Casio SK-1 go round and round, like a chu-chu train leaving the glitch station. The Gijs’ SK-1 device has bends patched to various places around the stationary contact wheel and while the arm twists around at various revolution rates glitches are triggered. The keyboard also has a custom PCB that controls the Pitch and Internal Clock Speed which is done through the use of an opto-transistor. Definatelly one of a kind mod, great work. Thanks to Karl and Gij’s for sending this in. More images on Gijs’ website.