Category Archives: Schematics

Schematics for various circuits.

Casio SK-1 Modifications from back when

Casio Twins sk-1 modified
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.

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Building Guitar Effects + Other Circuits

Random Note Generator
This link I’ve been hanging onto for over a year now, Laurier’s Handy Dandy Little Circuits. The guy has quite a collection of various Wah-Wah circuits ranging in complexity and features like an added Fuzz circuit. Through some browsing other little circuitry gems can be found including this simple oscillator collection and a random note generator. Good pleace to get some ideas for experimenting.

Casio Sk-1 with a Video Out

Casio SK-1 Video Out

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.

Casio SK-1 Video Out Circuit Bent