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Circuit-Bend Electronic Toys Into Sonic Monsters!

June 30, 2014
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Creative, curious minds have always modified and enhanced audio hardware. But in the past two decades, a growing number of people have hacked into circuits to transform simple instruments into alien beasts of sound.

THE TERM “circuit bending” was coined in 1992 when Reed Ghazala began publishing a series of articles in the Experimental Musical Instruments Quarterly Journal titled “Circuit Bending and Living Instruments.” Ghazala, who had developed his skills since the late ’60s, defined a couple of simple rules that would enable anyone to safely explore and modify audio electronics, without a degree in engineering.

About ten years later, the first annual meeting of circuit benders, the Bent Fest, was organized by Mike Rosenthal and Daniel Greenfeld at The Tank. For three days in the spring of 2004, this lively mid-Manhattan art space brimmed with energy from the many creative forces that came from all around the world to attend the gathering. The festival included workshops, tutorials, concerts, and showcases centered on the creative use of electronics that were not necessarily designed for the purpose of making music. This event, which lasted until 2011, became the annual meeting of the creative crop of circuit benders and hardware hackers, and was the birthplace of some highly individual electronics and sounds.

What is Circuit Bending? So, what is it, really? How do circuits bend? The short answer: Circuit bending describes the modification of an electronic sound device beyond the designer’s intentions, adding new sonic and functional possibilities. Although there are many approaches to circuit bending, in general, the bending target will preserve its normal operation and is just enhanced with switches, potentiometers, body contacts, or jacks that will invoke the functions or sounds.

Circuit benders usually are not electronics experts, nor do they have service and repair manuals for the devices to be bent. The process of bending is one of trial and error, carefully avoiding risking the health of both the bender and his target. Anyone, even children (supervised by a seasoned bender) can do it, as long as some basic rules are followed.

The Rules The first and most important rule is written in stone: Never bend anything that plugs into the wall. Circuit bending is strictly battery powered. The safety risk is just too great. The maximum voltage considered safe at all times is around 6-9 volts. That range complies with most common bending targets, which are powered by 4 or 6 batteries. (I make one exception with the Suzuki Omnichord, a wonderful bending target, which needs to be powered with 12 volts.)

Do not bend anything that you are dearly attached to, or is difficult to replace. Usually circuit bending does not harm your targets, but sometimes things go wrong and you might accidentally fry the piece you are working on. It has happened to me, so be warned.

Avoid contacts that produce loud pops and clicks, drop the volume substantially, dim displays and LEDs, or heat up components significantly. Also, avoid the area where the power supply connects, especially these pins on ICs.

Be aware of electrolytic capacitors. Elcos that are bigger than a cigarette tip can store a significant amount of energy that will melt the tip of a screwdriver when shorted. Never reverse polarity or they will explode. Wear safety goggles!

The Suzuki Omnichord OM-27 before and after bending. The three silver knobs on the lower side belong to a Ibanez DE-7 delay.
The Tools
You will need some basic tools to perform circuit bending:

• A set of screwdrivers (especially Phillips nos. 0, 1, and 2, and some flatblade models) to take apart the device. You’ll also need a set of watchmaker’s screwdrivers for tiny screws and to access individual points on a circuit board.
• A wire cutter, pliers, and a tweezer, to handle screws, wires, and other parts.
• A couple of cables with alligator clips.
• A low-wattage soldering iron and some solder. • A drill and a reamer, to make holes for the additional parts, such as switches and pots.
• Assorted parts: resistors, cables, capacitors, diodes, LEDs, body contacts, etc.
• Gaff er tape. This will help you to keep internal batteries in place.
• Helpful but not mandatory: a multimeter to measure voltages and resistance.

The Targets Okay, we know the rules, we’ve got the tools. What can be bent? Pretty much anything that is battery operated! I have seen people bring some awkward things to bending workshops, such as a broken wireless phone from the dumpster that was transformed into a funny dial-tone feedback-screamer. But usually, small keyboards, speech-generators, stomp boxes, drum machines, or cheap Chinese sound toys are common bending targets.

As a rule of thumb, consider the 1980s as the Golden Age of bending targets—especially the small keyboards manufactured during that time by Yamaha, Casio, and lesser-known brands that had very limited “intelligence” onboard. These instruments are easily “convinced” to interpret their operational information, hard-coded in ROM chips, in unusual ways by shorting some pins with other pins. This will lead to surprising and often beautiful results, soundwise, but also with the arpeggiator and play-along features of the instruments. Most modern synths with more sophisticated CPUs will crash when you attempt to bend them.

The basic bending tool for shorting selected pins on a circuit board. With two alligator-clip cables, you can place components such as a pot or a capacitor between pins.
The Yamaha PSS-270 and Casio MT-240, as well as speech toys like the Texas Instruments Speak & Spell family, are among the great bending targets, with simple logic and big, easily accessible ROM chips.

Some devices that off er very limited “standard” capabilities can be greatly enhanced with body contacts. The Suzuki Omnichord or the rare KoolShades Electronic Drum Set, or even a Boss Metal-Zone MT-2 distortion stomp box, are great body-contact targets.

It is a good idea to search the internet for information on the specific device that you intend to bend. Apart from instructions and how-tos (which in my opinion spoil the fun of exploring the possibilities), you will often find at least some feedback on the “bendability” of your device. Occasionally, and this is an exception to the rule, some instruments turn out to be duds, where no bending attempt shows any usable result.

Bending Techniques Bending targets are highly individual in terms of modifications that will work on them. There are three basic modifications that you can apply individually or combine on most of your bends:

Bending setup with bending box and external power supply from a 12-volt battery through an LM 317 power regulator. The target is a Casio SA-20.
Short two (or more) points on a circuit board. Depending on the instrument and your preferences, this is performed with a switch, a momentary switch, or through a patch bay.

Connect two points through a resistor of a specific value, or a potentiometer (which is an adjustable resistor). A special resistor that changes its resistance as a function of the brightness of light (LDR) is a nice mod that will allow you to use gestures instead of touching a knob to control your bend. For best results, combine that with a pot to control the range of effect. Often, resistors of any kind are combined with a switch to turn the bend on and off .

Use a body contact to make you part of the circuitry. By connecting one or more points you will act as a variable resistor, like a pot. The more surface you touch, the lower the resistance will be. Some connections will work only with a fairly high resistance. The resistance of your skin falls between 100 kilohm and 1 megohm depending on its moisture. If you have very dry hands, the resistance will be in the megohm range; if you have sweaty hands, it can be below 100 kilohm.

Other electronic parts, especially capacitors but also diodes, coils, etc., might have the right effect on your bending target. It is up to you to try them out.

Preparations Before we start exploring our target, we should prepare our setup. In most cases, you can open the target by loosening the screws on the back side of the instrument and carefully taking off the back. The wires connecting the battery compartment are often quite short and can rip off easily, so take your time.

The Casio SK-1 is one of the best-documented and explored bending targets, with a wealth of great bends and a stable and reproducible behavior. This model is enhanced with a breakout box for the additional components.
Now we should see some sort of circuit board, mostly showing the soldering side. Take a photo of the soldering side (and also of the component side, if easily accessible), and print out a couple of sheets. (I prefer bright, black-and-white prints.) This will be your “notepad” to mark the hot points on the circuit board and take notes about their behavior with other points.

It is always a good idea to write down the labels of the chips and Google them. For most chips, you will find data sheets that will explain their function and show the pin-out. That way, you will know the pins where the power supply connects, and avoid them.

It is tempting to just solder up whatever you have found, while exploring the circuitry. But the photo method will reward you with valuable info for later reference and encourage you to plan the best layout and bending technique before you start drilling holes.

Speaking of soldering: If you have never used a soldering iron, it is not a good idea to start soldering right on your bending target. Find an abandoned circuit board (such as a PCI-slot graphic card) to practice on; there are many great soldering tutorials out there on the web; see the “Helpful Links” sidebar for more information. After you have successfully soldered some cables to neighboring contacts on a chip, without shorting them or just “glueing” the joint (by not heating it up enough), you are ready to work on your bending target.

Fig. 1. The circuit board of the Casio SK-1. Here, three double rows of pins mark the ROMs. Note two main-points on the ROMs, and some of the interesting connections. There are many more possible connections, but not every single pin needs to be checked; some of the pins already connect to others on the same or another ROM.
Let’s Get Started!
For this example, we will bend one of the most rewarding and iconic bending targets, the Casio SK-1 sampler. After batteries are fixed in place, we will start our exploration by checking the circuit board for chip-pin patterns.

On the left side of the circuit board, three vertical double-rows of pins indicate the three ROM chips; this is where we start (see Figure 1). Now we need our alligator clips. Link two watchmaker screwdrivers with it, and presto—there is your “precision bent-point detector.”

Now we come to the somewhat uncomfortable fact that we need make the instrument play while we are working on the back. Luckily, most synths have demo songs that start on one button press, so we can use those and concentrate on the backside. Choose one of the pins as a master pin and connect that to all other pins on the ROMs, while the demo song is playing. You will notice the sounds and playback patterns change significantly, but the connection of some points will crash the instrument; you will know this has happened when the sound freezes or mutes and nothing happens when you press any buttons or keys. This is not a big issue or reason to worry. Disconnect the battery or switch the SK-1 off and back on and start over. As this procedure is somewhat tiresome, I install an NC (normally closed) momentary switch into the positive battery wire (red), so I can reset the SK-1 with the push of a button, with easy access.

The KoolShades drum toy is a very lively body-contact bend. Note the upholstery tags used for the body-contacts and the mark sheet.
In addition to the ROMs, you’ll often find some kind of tuning trimmer. You can connect that with a variable resistor, like a pot or an LDR, or a combination of both, to certain points on the circuit board. Sometimes these trimmers relate directly to the speed of the CPU; to keep it from crashing, a minimal resistance needs to be detected and inserted as a resistor at the wiper (middle) lug of the pot. Be sure to make this mod switchable, so you can always fall back to the original tuning.

Over time, you should have marked the good and bad spots on the ROMs; now, think about your preferred way of making them accessible. There are many ways to do so, especially with the Casio SK-1. (For inspiration, search the Internet for pictures of bent SK-1s.) The space inside is too tight for everything to be wired up in the instrument itself, especially if you don´t want to sacrifice the speaker. So, if you like to max out the possibilities, it might be a good idea to use an external box and use a multicore cable to connect your switch or patch-board to the SK-1.

The procedures described here apply for pretty much all keyboards with ROMs. If the target is based on FM synthesis, such as the Yamaha SHS-10 or PSS-270, cutting the data lines between FM chip and CPU and rewiring them to switches will bring out the amazing sonic possibilities of FM synthesis beyond the “normal” sounds found in the instruments.

Body Contacts One of my favorite bending techniques is the use of body contacts. Body contacts provide very tactile and sensitive control of a connection; unlike switches or pots, they are as subtle as the fretboard of a violin, altering tone and timbre with the slightest movement. Almost every bending target has at least some body-contact points at the amplifier section. But usually these produce only very loud feedback.

But some bending targets, especially ones where the sounds (or lots of gain) are produced by analog circuitry, offer a wide range of feedback, at a controllable level.

Finding body contacts is really easy, and it’s the first thing I check on any bending target. I simply touch the circuit board with my fingers (moistening them a bit if they are very dry). If you have found areas that work nicely, it is time to grab the watchmaker screwdrivers (this time without an alligator-clip cable between them) and break things down to individual points.

The best way to make those points accessible on the outside of the instrument is to use upholstery tags. These are cheap, easy to install, and have a nice feeling to the touch. Most importantly, you can solder wires directly to them. Drill a hole slightly smaller than the tag’s pin, push it through the plastic case, bend it a little to keep it in place, attach the cable, and you are done.

One of my favorite body-contact feedback screamers does not even need that step. The Boss Metal-Zone MT-2, a distortion stomp box with high, low, and parametric EQ, has so many interacting points that I just sanded down the spiky pins on the board and rehoused it in a lightweight plastic case.

Above right, bending box; below, its schematic. Note that the resistor cascade can be used in series with all other components with the switches S1-S3.
Tool of the Pros: The Bending Box
If you like to practice circuit bending on a regular basis, you may want to optimize the process of exploring your target. A really helpful tool that you can easily build yourself is a bending box, which will contain assorted common components like a switch, temporary switch, body contacts, LDR, LED, capacitors, and a resistance decade. A resistance decade is made of pots connected in serial, with a resistance that increases ten-fold with every pot: 10 ohms, 100 ohms, 1 kilohm, 10 kilohms, 100 kilohms, and 1 Megohm would be the values of choice. This tool will enable you to precisely dial in any value between 1 ohm and 1 Megohm, which is very helpful to determine the best resistance or pot-range value for your special bend connection.

The bending box I built for myself also doubles as a power conditioner. I use a 12-volt gel/lead-acid battery through a simple circuit around a LM 317 power regulator, which lets me dial in any voltage between 3 and 11 volts. Gel-lead batteries are cheap, reliable, and will easily work for a decade if you charge them properly after every use and never deplete them fully.

I’ve only introduced you to the basics of circuit bending. There is so much more to learn and explore. Check out the books and Links listed here for some inspiration—and have a nice bend!

Joker Nies lives in Cologne, Germany. He is a musician, recording engineer, circuit bender, and editor for Sound & Recording and Keyboards magazines. His circuit-bending career started in 1995 with a Suzuki Omnichord OM-27, which is still one of his favorite instruments to play.

Bending Targets

These are bending targets with proven bending potential. This list is in no way complete; you will find more models on the internet.

Keyboards
Casio SK-1, SK-5, SA-2, MT-240, SA-10, MA-101, Concert Mate 380 (SA-2)
Yamaha PSS-270, PSS-470, PSS-780, PSS-790
Fujitone 3A
Neurosmith Musini

Speech Toys
Texas Instruments Speak & Spell, Speak & Math, Speak & Read, Touch & Tell
V-Tech First Talking Computer, My Little Talking Computer, V-Tech Apple
Hasbro Furby

Guitar FX
Distortion/body contacts: Boss MT2 Metal-Zone, Boss DS-1, Pro Co Rat
Delays: Ibanez DE-7, DL-10

Drum Machines
Korg DDD-1, DDD-5
Roland TR-505, TR-626
Yamaha DD-6, RX-11

Reference Books

A great guide to start out with, especially if you are totally inexperienced with electronics, is Reed Ghazala´s Circuit Bending: Build Your Own Alien Instruments. The master shares his knowledge by explaining every step, electronic component, and technique carefully and in great detail, for many bending targets.

Another great read, with lots of examples from the world of hardware hacking, is Handmade Electronic Music: The Art of Hardware Hacking by Nicolas Collins. It also starts with detailed basics and unfolds into building your own little sound circuits. It also features an amazing collection of examples from sound artists, in pictures, description and sound (on DVD).

Finally, a wonderfully hand-lettered and drawn book to help you get familiar with electronics: Forrest Mims III’s Getting started in Electronics. Its appealing drawings make this book an easy-to-understand read, covering all aspects and components of electronics.

Helpful Links

Reed Ghazalas’ informative homepage, with lots of info and photos of his gorgeous creations: anti-theory.com.

Issues of the Experimental Musical Instruments journal are still available online on CDROM, in case you want to read Reed Ghazalas’ original articles on circuit bending: windworld.com/productspage/back-issues.

A great soldering tutorial in comic form: mightyohm.com/blog/2011/04/soldering-is-easy-comic-book.

A great collection of information on many common and rare toy keyboards and bending targets: weltenschule.de/ tablehooters/instruments.html.

Lots of info on all aspects of the topic: getlofi.com.

This page specializes in stomp-box mods: circuit-bent.net/effects-pedals.

The British branch of circuit-bending; many drum machines found here: circuitbenders.co.uk

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