This circuit is constituted by three simple synthesizers based on oscillators (555 timers). It was conceived and built by Alessandro Perini (with the precious help by Gualtiero Piazzi) for a music performance commissioned by Milano Musica and premiered in November 2019 at Teatro Franco Parenti (Milan, IT), with Francesco Dillon (cello) and AGON (sound). This concept can be adapted to other purposes - the cello strings being interchangeable with any other conductive object or material.
You can find more info and download the full score of "Touch Me" at this link. The score also contains details about how to build the bow and how to equip the fingers, issues which are not covered here.
Excerpts from a performance made with the described circuit. The three oscillators were connected to cello strings, which were thus part of the circuit. Hands capacity, and capacitors worn by Francesco Dillon on his fingers, were used to produce pitched sounds and noise.
Since the circuits are open (see the alligator clips in the schematics), the whole piece is based on producing sounds by closing those circuits, thus letting the current flow. Each alligator clip is connected to one of the cello strings. The A string is the common negative to all the three circuits; connecting the A string with any other string will close the respective circuit. If you are not using a cello, and probably you are not, a capacitor which connects the black alligator clip with one of the other clips will sound (some very low or very high capacities will produce infra- or ultra-sounds, though). Unexpected interaction between the circuits is obtained with crossed and combined connections between the strings.
In this configuration, to obtain audible frequencies and noises, the strings should be connected so that the current flows through capacitors. In my piece, the performer operates capacitors in three different ways:
wearing capacitors on her/his hands. Fingertips are equipped with metallic terminals, and capacitors are mounted in series between each finger;
Capacitors on the left hand. Wired terminals are on the fingertips.
using a custom-made “capacitor-bow”. A wooden stick with different capacitors mounted in series;
Custom-made "bow" with different capacitors in a row.
using her/his own hand flesh. Flesh has its own capacitance and it varies with pressure and with how much surface is in contact with the string.
You can try different capacitor combinations to see which ones sound good for your purposes. For this reason, I recommend to buy a package containing a variety of capacitors of different sizes. Also, you can alter the rest of the capacitors or resistors in the 555 configuration, to change frequency and duty cycle. In the configuration described here, placing a small capacity between the black alligator clip and another alligator clip will result in a high-pitched sound; conversely, a large capacity will lead to a low sound, even a pulse. You can use this website to calculate beforehand which sound will come out from a particular combination of resistances and capacitors. Check this other page to learn more about the 555 timer and its different behaviors.
Final look of the finished and encased circuit (no lid yet!). I used the plastic case of an old router. I even used its bipolar power switch, which turns both power sources (battery and adapter) on or off at the same time, while keeping them isolated.
Some tips:
As you can see from the picture above, I included a 4, 5V case for three AA batteries, but I discovered the sound doesn’t get the same good distortion as with the wall plug, so it remained unused.
Power adapter: for safety reason, make use of a double-insulated one (symbol of two squares, one inside the other). This is needed because the performer is directly touching part of the circuit, which is connected to the power supply (safety on the amplifier side is guaranteed by the opto-isolators).
Regarding male jack outputs: it would be clever to use female instead of male jacks, for the sake of easier connection capabilities to mixers or DI boxes. Don't replicate my mistake :)
The knobs are used to tune the oscillators (except for the very low one) and adjust the volume.
1 / 4 • Final look of the oscillator box and some more making-of pictures.
Three 555 timers are used in astable mode to create oscillators. For each circuit, one capacitor is disconnected and can be inserted on-the-fly for producing different pitches.
Touch me - Circuit - Pdf file
Three 555 timers are used in astable mode to create oscillators. For each circuit, one capacitor is disconnected and can be inserted on-the-fly for producing different pitches.
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