Reed Ghazala, author of this article, wrote an extensive series of articles for the Experimental Musical Instruments quarterly journal between 1993 and 1999. For a fuller exposition of his circuit-bending techniques, you can find the last of this series, published in EMI in June 1999, posted on the Oddmusic web site.

This article appeared in Experimental Musical Instruments Volume 12 #2, December 1996. The print version of the article contains several photos and an additional sidebar not contained in this version appearing on the World Wide Web.

Copyright 1996, Q.R. Ghazala..

The Casio SK-1: Escapist Sample Shuttle

By Q.R. Ghazala

The glass in my workshop window is 70 years old. Its thickness varies, and the world outside passes by in fluid, undulating waves. In the cracks of this glass, where a forgotten autumn's chore may have left its mark, can be seen all the colors of the rainbow, refracted splendidly for anyone given to close inspection. Glued to a rippled pane, a fine rubber skink watches a small cricket climb up the yellowed edge of an old skyharp postcard. Through the Victorian crystal teardrops and hanging stained glass spheres, through the pinned-up templates and photos and chipped green paint of the window's dusty sash flows the orange evening sunlight, wavy after passing through the magic window-lens. A breeze comes now and gently swings the antique glass balls, their projected optical flares rocking back and forth upon circuit drawings, colored-light fairies on a rippled orange sea.

The plans, today, upon which the fairies dance are those of the circuit-bent Casio SK-1. ("Circuit-bending" refers to the process of creative short-circuiting by which standard audio electronics are radically modified to produce unique experimental instruments. A further description of these techniques can be read in EMI Volume VIII #1, 1992.) Readers of this article series have inquired over the years about the viability of keyboard instruments as a focus for circuit-bending. While I'm inclined to think the end result of the bending process is often better suited to less linear sound machines, keyboards were an early target of mine, and the circuit-bent SK-1 is an exceptional example of deep-end anti-theory application combined with equal-tempered polyphony. Abstract sound fields thick and intriguing, complex voices, split keyboards, strange tone shaping and extended ADSR envelopes begin the list of new possibilities... but more on such things in a moment.

Casio's SK-1 introduced digital sampling to more individuals than any other sampler to date. The SK-1 began to appear on store shelves in 1986. For its time, at its price and with its functions, there was nothing else like it. Main features of this 32-note mid-size keyboard include:

- 4-note polyphony, available live and also in memory for digital record/playback functions of two types: 1) real-time 4-note polyphony, and 2) 3-channel multi-track memory coupled with a "one key play" system allowing notes in memory to be manually sequenced for editing purposes;
- 5 PCM voices, 1 user-sampled voice, 3 harmonic synthesis voices and one user-adjustable harmonic synthesis voice (this nice feature provides a tone in which most of the first 16 harmonics are present and can be adjusted in strength, with up to 14 levels of accentuation for each);*
- Thirteen different preset ADSR envelopes which can be applied to any voice in use;*
- Preset portamento and vibrato effects;
- 8 bit PCM sampling at 9.38 kHz (sample time is approximately 1.4 seconds);
- Built-in condenser microphone for inputting samples, as well as two input jacks line and external microphone;
- Line-output;
- Master tuning;
- 11 auto rhythms with chord accompaniment;
... and lastly, that button everyone dreads hitting by accident... the Demo Tune (which circuit-bending reconstructs in a wonderfully irresponsible manner).
*PCM (Pulse Code Modulation) is a high-quality means of digital audio data processing. ASDR (Attack-Decay-Sustain-Release) describes the four main parameters of sound envelope transients as commonly addressed in electronic synthesis techniques.

No, it's not a hi-fi sampler. But thousands of people found the SK-1's audio quality good enough to keep interest on high for some time.

Plenty of SK-1s are still around today, patiently waiting to be reborn through circuit-bending. Since the resultant instrument is so exotic in its behavior, so intriguing in its sounds and so attainable through standard rewiring techniques, I'll devote this column to the SK-1's anti-theory transformation.

My first SK-1 was bought during its heyday at a price of around $90. I quickly made two modifications and, until lately, thought no further about altering it. These early changes resulted in two jacks being mounted on the SK-1's case. One was wired so that it would accept a remote sampling trigger to use in conjunction with an external microphone. The other jack was wired to accept programmed voltage pulses (such as those generated by drum machines) so as to trigger the "one key play" function thereby turning the SK-1's note memory into a nicely controlled sequencer. Push "start" on the drum machine and both it and the SK-1 perform in tight synch. Fun.

Years pass... the SK-1 is overshadowed by industry changes and pushed to the back of the shelf (go take out those batteries!). Few things tend to encourage a circuit-bending experiment more than finding a promising target device at a bargain price. Especially if the device is a duplicate of an item you already own and care for, and is one you'd like to bend but are hesitant for fear of damaging it in the process. So I was thrilled to recently find a SK-1 (with a key missing) for only $1.50 at a thrift shop. Oddly, several days later I found another SK-1, this time in great shape and costing $5.00 at a different second-hand shop. The one with the missing key became my prototype, the $5.00 unit became the finished instrument and my original SK-1 remains as it was before.

Following the usual process of circuit-bending, the instrument was expanded upon to the degree of now providing 28 new controls (switches, dials and body-contacts), 7 micro green & red LED logic pilots and an ultra-bright sound envelope LED... 36 modifications. With all the added controls turned off, the SK-1 operates as normal. The modifications are easy to find and are open to anyone familiar with the use of a soldering pencil (small, low-wattage soldering iron).

Once again, the creative short-circuit is on the loose, the repercussions of its catalytic anti-theory wreaking indeterminate digital havoc within the all-too-proper halls of previously strict program logic. The new controls were discovered one of two ways. Either by listening to the instrument's voices while 1) using a wire to momentarily connect arbitrary circuit board points to each other (this giving rise to 20 of the 22 circuit-bending switches, their purpose being to implement and combine the creative short-circuits just found), or 2) using fingertips to connect arbitrary circuit points to each other (the 3 body-contacts and 2 of the 3 dials [potentiometers or pots, variable resistors] were found in such a way).

This last activity, touching an active circuit-board with the fingers to hear what changes occur in the sound, should be done only with low-voltage, battery-powered circuitry. Circuits containing large capacitors or step-up transformers are to be avoided. These are simple to recognize; check out a beginner's electronic Project book if unfamiliar. These components usually appear in various types of lighting circuits, practically never in the audio electronics appropriate for circuit-bending. At any rate, the idea is that interesting sounds arising from finger contact can be hard-wired into existence by soldering a pot (variable resistor) between the two points so discovered. The middle solder lug of the pot is wired to one circuit point, an outside lug of the pot to the other circuit point. After all, that's exactly what your body is doing in the same situation. As the electrical energy is conducted through your flesh its potential changes as you vary the resistance presented it by adjusting the pressure of your fingertips on the circuit-board. You've become, in essence, a variable human resistor (aren't we all?). Conductivity will differ from individual to individual, so there is no exact recommendation I can give as to the resistance rating of the pot. Experiments with a 500K will provide a good starting point.

My SK-1 circuit-bending applications fell into 9 sections. These are the IMAGE GROUP of 9 switches, the SKEW GROUP of 7 switches + 1 pot, the BODY CONTACT GROUP of 3 brass spheres, the PITCH control dial, the POLY control dial, the AXIS GROUP of 3 switches, the RESET GROUP of 2 switches, the LOGIC PILOTS GROUP of 7 LEDs + on/off switch and, lastly, the SOUND ENVELOPE LED. None of these expansions of the SK-1 were hard to find. Following are brief explanations of these new circuit-bending discoveries, as well as guidelines for implementing the changes yourself.

1) Though it seems I haven't harmed any normal functions of my 3 SK-1s, there's no guarantee that a connection I didn't try exists that could damage or destroy the circuit. In the same vein, manufacturer's design changes can create a situation in which a previously trusted circuit-bending connection becomes either inoperative or destructive on a later model. Therefore, while my instructions are valid in pertaining to my SK-1s, they may not be advisable for yours.
2) The bending procedure requires a great deal of soldering tiny wires to very closely spaced IC pins protruding through the underside of the board. Very careful connections need to be made in order to avoid creating solder bridges between the pins. Quick connections are also a good idea so as not to overheat the internal IC electronics connected to the pin. I use a 30-watt grounded soldering station with long, tapered, 1/16" wide chisel-tip on the soldering pencil. For point-to-point connections I use insulated bought-in-quantity 30-gauge "wire-wrap" wire, the wilder color the better, and lead-free silver electronic solder.


[Note for web-site readers: while the descriptions that follow will stand on their own, the photo of the circuit-bent SK-1 that accompanies the print version of this article (EMI Volume 12 #2) will help in orienting the reader. The photo contains small lettering which would not reproduce legibly on the screen.]
For persons interested in experimenting on their own SK-1s, my descriptions below assume the working orientation of circuit is such that the underside of the board faces the experimenter and that the parallel grouping of three large (28 pin) ICs is to the bottom left (on reverse of board). In this position a medium-sized electrolytic capacitor is situated at the top right corner of the circuit-board. This needs to be relocated elsewhere within the case (on insulated wire extensions) to open up room behind it for new controls to be mounted.

Image Group
These 9 switches to the right of the keyboard are interconnected between various pins on the furthest to the left of the three ICs mentioned earlier. Experiment to find these connections and others. Turning these switches on singly or in combination will create up to 8-step sound envelopes, up to five keyboard split points (different sounds assigned to various key groups), oddly evolving tone clusters and extended decays lasting up to 30 seconds or more. The multi-step sound envelopes may combine voices from the SK-1's menu or create new voices, changing voices, strung end-to-end and finally settling upon an unusual sustained tone, or slowly fading away. Additionally, choosing a different voice from the menu may completely change the effect of a given IMAGE switch.

Skew Group
These seven switches and 10K pot make connections between various pins of the same large IC and a common point on the bottom right-hand side of the board, that being to a pin on the 14-pin chip just to the left of a board mounting screw. Again, experiment. Essentially, the five main SKEW switches connect five pins of the large IC to the smaller IC by running through one of the other two smaller switches in the group. This signal also passes through the 10K pot. The pot adjusts the strength of the signal passing between the two chips, and the smaller push-button and toggle switches allow the choice of either intermittent or continual use of the chosen SKEW effect while playing. So if, say, SKEW switch 1 is turned on, a connection is made between a pin on the large IC and the pin on the smaller one. The intensity of the effect is governed with the SKEW pot, and the musician controls the duration of the effect with the two miniature actuation switches. The SKEW effects are similar to the IMAGE effects with the addition of adding pulsings to final voice segments of multi-step sound envelopes. Assorted sustains, echoes, repeats, doublings, choruses and harmonic distortions also arise from the SKEW effect group.

Body Contact Group
These three brass balls are wired to three circuit traces just to the left of the master tuning trim pot soldered into position in the center of the board. Primarily pitch controls, bridging with a fingertip the gap between the center sphere and the one to its left will lower the frequency. Bridging the gap between center and right will raise the frequency. Actually, just touching either outside sphere will bend the frequency, but not as dramatically as when bridging the gaps as mentioned. Very nice real-time vibrato and pitch-bend are possible in this way. Beyond this application, a moistened fingertip pressed across all three contacts will bring on an assortment of deep-end audio calisthenics simply impossible to describe! Tech Note: On a crowded circuit board it can be hard to tell just which traces your fingers are touching to create the audio changes heard during this process of exploration. Holding a metal jeweler's screwdriver in each hand will allow you to touch obvious and specific traces on the board. Electricity will flow into one screwdriver, through your body and out the other screwdriver back into the circuit. Varying hand pressure on the screwdrivers will allow you to observe the effect of changing resistance between the two potential body-contact points.

Pitch Dial
This is simply a 500K pot wired between the two outside body contacts. Decreasing the resistance raises the overall pitch of the instrument.

Poly Dial
Another 500K pot, this one is connected between the right-hand lug of the SK-1's on-board master tuning trim pot and any of a number of potential traces on the board. Try traces an inch or so below center mounting screw. When the resistance is decreased, a note or two of the polyphony will slowly fade out. This control is used to adjust the degree of polyphony, especially valuable when applied to the dense abstract sound fields generated through other circuit-bending controls.

Axis Group
These three switches connect a pin on the large left-hand 28-pin chip (again) to three pins on the two 28-pin chips to its right. Many possibilities here... experiment! Drastic voice changing in the form of distant ethereal sounds, rich tonal swells, seemingly chance music cycles, metallic percussive bursts and endless de-tuned sustains are a few of the effects created by the AXIS GROUP.

Reset Group
These two switches represent a choice of "HARD RESET" or "SOFT RESET". As I've stated before, the unusual anti-theory design system of circuit-bending can create digital exasperation in logic routines, otherwise known as program crash. When the circuit-bent SK-1 crashes (and it will), four reset options are available. Casio's front panel "RESET" button might work. If not, turning the SK-1's main power switch off and back on might work. If both of these fail, my "SOFT RESET" miniature push-button on the left side of the case could solve the problem. This makes the same connection as IMAGE switch 2. During initial prototyping I noticed that this connection could reset certain crashes without powering-down the unit. Yes, I could just flip IMAGE switch 2 on and back off, but the mini push-button is easier, quicker, and more out of the way while playing. The "HARD RESET" is a "push-on/push-off" switch situated next to the mini switch just mentioned. This is the deep crash remedy since it completely breaks the circuit between the power supply and the board. Therefore, it is also a MASTER POWER switch. This is the standard reset I include on many circuit-bent instruments prone to crash. Can you keep a secret? It does the same thing as the tiny reset switch you're instructed to push with a pencil tip in case of malfunction of your calculator, answering machine, musical keyboard and lots of other digital whatevers. Yep, the Big Guys' theory-true toys crash deep enough all by themselves to need as drastic a thing as battery disconnection to set them straight again too!

Logic Pilot Group
This group of seven miniature red or green LEDs is implemented by connecting the anodes (+ leads) of the LEDs to various pins of the large right-hand 28-pin chip. All LED cathodes (- leads) then connect through a LOGIC PILOTS power switch (on back of case) to the negative side of the power supply. The switch to turn them off is needed for two reasons. First, if left on they continue to drain power unless my added master power switch (HARD RESET) is turned off. Second, certain IMAGE switches overdrive the LEDs when turned on, risking eventual burnout. These LEDs flash mysteriously as logic levels (voltages) go high or low as the instrument functions. These can also be considered STATUS LEDs, and can be quite informative when gotten used to on this and other circuit-bent instruments. I've drilled holes for these along the top of the SK-1's case with a few also mounted below, amidst the control buttons. Circuit connections for these are discovered the same way as switch connections. Simply use LEDs with alligator clip test lead extensions in place of the usual short-circuit exploration wire. Remember that LEDs are polarized semiconductors: if an LED won't light, try reversing its leads and reconnecting it to the circuit. If an LED glows too brightly or gets hot, try connecting a resistor (experiment around 100 ohm) between the LED's anode and the circuit.

Sound Envelop LED
This clear, bright, red LED (2,000 mcd) is connected across the speaker terminals and fluctuates with the intensity of the sound without disturbing sound volume or clarity (which is not always the case with this parallel wiring scheme). LEDs can also be connected in series with a speaker if more energy is needed to drive them. Sound envelope LED connection points can also be found by attaching one LED lead to a speaker terminal and then touching an extension of the other LED lead to various parts of the active circuit. In fact, such envelope LEDs can be driven by points discovered on the board having no direct connection to the speaker whatsoever.

As noted before, circuit-bending the SK-1 does require a good deal of careful work since tolerances of both soldering and component placement are tight. Much more is possible than what I've done. Still, a person might want to add, say, only a body-contact and leave the rest of the SK-1 untouched.

Any newly bent instrument presenting significant sound forms deserves a visual transformation as well. Once the holes were drilled to accept the new switches, pots, LEDs and body-contacts, I painted the case of my circuit-bent SK-1 a hi-gloss fire engine red. Over that went a flat black crackle coat. This is a type of paint that contracts and cracks apart as it dries, leaving an organic-looking and somewhat fractalized pattern. From far above the case a sweep in the air of holographic micro glitter (several specks could fit in the dot of this letter i) was rained down onto the housing, falling like a star field across the scarlet veins in the black crackle field. These tiny particles reflect a brilliant spectrum of light, shifting hue in unison as viewing angles change.

A high-solids clear gloss final coating was then applied. This deepens colors, serves as a sealant and provides a surface upon which an extra-fine-tip opaque paint marker can be used to label the new controls, and re-label the old, their having been painted over in the refinishing process. New controls are then mounted, unit is reassembled and wiring is begun. With the SK-1 I decided not to refinish either the case bottom or the strip above the keys that contains envelope symbols.
Be forewarned that if you decide to dismantle the entire device to refinish the case as I've done, the keyboard "trees" need special handling. All the keys, in separate sets for white and black, are connected to a common tree and remove as single units. It is the junction of key-to-tree that is very fragile and must be handled with real care. It takes little force to bend a key out of alignment or snap it off completely.

Exploring the SK-1 circuit is fascinating. In the EFFECT GROUP discussions above I've only begun to describe the major effects available within the separate groupings. Not only can each group be depended upon to produce many more effects than those covered, when multi-group combinations are experimented with (e.g. IMAGE switches 1,3,7 + SKEW switches 2,3 + AXIS switch 1 while touching body-contacts or sweeping POLY dial), the surprising nature of circuit-bending's ability to always generate new audio behavior becomes evident. My initial examination of such switching combinations produced 30 strong variations using the PIANO voice alone.

On some deep-end settings the circuit-bent SK-1 becomes an aleatoric music box, evoking outlandish chance compositions. Other settings turn the keyboard into an alien sound field generator, intercombining curtains of relatively pitch-free noises. Peculiar mixtures of countless types emerge as one moves deeper into switching possibilities... and I now find myself in the position again of trying to describe the eccentric, many-nuanced voices of circuit-bending. Like trying to define a rare flavor or shifting color.

As it often is with circuit-bending, these more extreme settings impose a control/non-control balance that can take some getting used to. Program crash is often inevitable under these conditions. Charting patch settings and sequences goes a long way to establish reliable interactions, but the temptation to go a step further and see what happens is always there. I accept, even enjoy the non-control aspects of circuit-bending, feeling that they add to the mystery, and knowing that they are an integral part of the whole fascinating process that I've grown to enjoy so much. I'm reminded of the orange evening light through my wavy glass, and the prismatic fairy-flares dancing along its crests upon my SK-1 plans as I sat down to begin writing this article.

I'll admit I thought for a moment of turning on the overhead drawing lamp, chasing the light fairies away so I could better see my notes. But you know, I didn't.


Reed Ghazala can be reached at :

E-mail:  Anti-Theory
POB 20181
Cincinnati, OH 45220


Reed's full-color Anti-Theory Workshop catalog is now available. A visual treat itself, the 8-panel brochure depicts 19 different instruments and three of Reed's recent music packages. To receive a copy send $1 and a self-addressed stamped envelope to the workshop address above.