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Casio SK-1 (SK1) Mod: your own sounds in the preset ROM

Swap the preset ROM of the Casio SK-1 (SK1, also sold as the Realistic Concertmate-500) for an EEPROM and fill it with your own sounds. Free, open source, and tested on a real SK-1.

ROSETTA OS // SK-1 STUDIO
SK-1 Studio on GitHub The hardware mod

Works on a real SK-1

Drop-in EEPROMA Winbond W27C512 goes in the preset ROM's socket. No other changes to the board.
Your own presetsThe 5 sampled presets replaced: an overdrive guitar chord, a Mellotron choir, a Chamberlin voice, a poly synth and a sci-fi FX.
3-second soundsOne sound can fill the whole ROM: 3.2 s, against 0.4 to 0.9 s for the stock presets.
Custom loop pointsHold a key and the sound sustains on a custom loop instead of stopping.
Stock in one swapPut the original chip back and it's a stock SK-1 again.

SK-1 Studio

A Windows app that builds the ROM for you. Load a sound into each of the 5 preset slots, hear it the way the SK-1 will play it, and burn the chip.

SK-1 Studio main window
Each slot takes a WAV, a sample from a Roland S-760/S-770 CD image or an Akai S1000/S3000 CD image (.iso, .nrg).
SK-1 Studio loop editor
Loop editor: drag the loop start and end on the waveform, snap to zero crossings, set the crossfade, play the loop.

How it works

  1. Desolder the preset ROM (LSI2, NEC D23C256EAC-011) and fit a 28-pin socket.
  2. Read your own chip on a programmer such as a T48 and keep it.
  3. Build your sounds in SK-1 Studio on top of that dump and burn a W27C512.
  4. Fit the W27C512 and play.

The SK-1's own sampler stays as it is (1.4 s at 9.4 kHz). The mod adds custom samples in the preset ROM. For longer self-recorded samples there are notes on a clock mod.

SK-1 mod FAQ

Can you change the preset sounds on a Casio SK-1?

Yes. The SK-1's sampled presets sit in a 32 KB ROM chip (LSI2, an NEC µPD23C256). Swap it for a Winbond W27C512 EEPROM holding your own sounds, built in SK-1 Studio. Tested on a real SK-1.

How long can a sound be?

One sound can fill the whole ROM: 3.2 seconds at the SK-1's own 8-bit, 9.4 kHz. Five sounds share that space, so each is around 0.6 s, and one of them can loop. The stock presets are 0.4 to 0.9 s.

Can the SK-1 record samples longer than 1.4 seconds?

Not with this mod: the 1.4-second limit of the SK-1's own sampler is set inside its CPU. A slower clock gives longer, lo-fi samples; see the clock mod notes.

Do loops work?

Yes, tested on a real SK-1: one preset can loop, so a held key sustains instead of stopping. SK-1 Studio's loop editor sets the loop start, end and crossfade.

What do I need?

A 28-pin socket, a W27C512 (or another 27C256-pinout EEPROM or EPROM), a programmer such as the XGecu T48, a desoldering tool for the old ROM, and a Windows PC with Python for SK-1 Studio.

Does it work on the Realistic Concertmate-500?

The Concertmate-500 is Radio Shack's version of the SK-1, and its service manual describes the same board. It should work the same way, but it hasn't been tried on one yet.

Is Casio's ROM included?

No. You read your own chip and SK-1 Studio builds on that dump. A good SK-1 dump has CRC32 d615963c.

Community

Questions, hardware reports and ideas: join the Discord. More Rosetta OS mods: Roland D-110, SP-808, Akai S2000, GP-16, U-110.