A few years back I received a birthday card that, when opened, played a 15-second clip of The Final Countdown. Before tossing it out, I tore the little board and speaker from the card. I knew nothing about electronics at the time, but I just thought it was worth keeping around.

The audible gates of Hell.

The audible gates of Hell.

Well I found the little device in one of my junk containers last week and immediately recognized it as something to be circuit bent. The board had an IC, a capacitor, and two resistors. As I learned from Nicolas Collins’ excellent Art of Handmade Electronic Music, one of those resistors was the freakout resistor. Following his “laying of hands” technique, I licked my finger and ran it around the board while the circuit was on. This actually worked very well as I immediately found the resistor that caused the sound to go all wonky.

The basic idea here is that the circuit operates at many cycles per second, at a rate determined by some resistor. If you change the value of the resistor, that rate will change and the audio clip will either speed up or slow down; this is the basic idea behind circuit bending. When you run a damp finger across the board, you’re making random connections and changing how components interact with each other. When you short out the clock resistor, it sounds like hitting the circuit’s main nerve.

So now with the clock resistor found, the next step was to replace it with a potentiometer so that the clock speed could be manipulated with a twist of a knob. After removing the resistor from the board, I measured its value as ~400k and set out to find a potentiometer in the same range. I was very happy to find a 2 megohm pot in the parts hole at the space since it would slow the clock quite dramatically, producing some really cool roaring depths-of-hell sounds.

Trimpot between output wires.

Trimpot between output wires.

The board had an integrated 3V watch battery which I replaced with a 2-AA holder. There was also a mechanical contact on the board to turn the circuit on when the card was opened; I replaced this with a simple toggle switch. I also thought it would be cool to switch back and forth between normal mode and circuit-bent mode, so I used a DPDT switch to toggle between the original clock resistor and the circuit-bending potentiometer.

Lastly, I wanted to add 1/4″ output to the circuit. That way it could be amplified, distorted and subject to all sorts of effects and processing. I cut the wires leading to the little speaker and soldered them to the signal and ground leads of a 1/4″ output jack. This arrangement alone would have been far too much to run into an instrument amplifier, so I soldered in a trimpot to act as a volume control (and/or load resistor taking the place of the speaker) between the output wires.

Guts.

Guts.

I neglected to consider an enclosure for this project. However, I did notice an alarming surplus of queso dip at the space. Since apparently nobody likes queso, I emptied a jar, cleaned it out (probably the hardest part of the whole project) and drilled some holes in the lid to accommodate my components. A coating of white spray paint covers the Tostito’s logo for extra class. I actually really like this au-natural enclosure since you can see all the components and wiring just hanging there. Since nothing’s fixed down, I hot-glued all my solder connections to the board. I think I’d like to experiment with glass jar enclosures again, perhaps with some lighting involved next time.

In the process of building and testing I noticed that when I would touch the third, unused lug of the pot, I could get some cool scratchy AM Radio static sounds from the circuit, especially with the pot wiper all the way over in satan mode. So as a last minute little addition, I soldered a bare wire to the lug and ran it outside of the jar to retain this touch-sensitive flavor of noise.

And that’s how you make Dan’s homemade queso dip.

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