Part 1. Lunetta synths create sound by using digital logic chips. They’re very easy to build and so much fun. With just a few parts you can make a square wave oscillator, sequencer or noise machine. In this article, we take a look at the Quad NAND CMOS chip as a Lunetta.
My first introduction to Lunetta synths was when I read the classic DIY book by Nicolas Collins. In Handmade Electronic Music he explains how these chips can function as fun little electronic instruments.
This article series is inspired by his CMOS Quad NAND Gate Schmitt Trigger Circuit. Albeit with an interesting little
bug 😱 twist in the end. We also work towards a Lunetta module suitable for your Eurorack system.
What is a Lunetta Synth?
The concept is called after Stanley G. Lunetta (2016) who didn’t like that it was named after him. He used logical CMOS chips to create interesting sound circuits. This is how.
The output of a logic operation is digital. This means that they only put out a certain voltage level or ground. High or low. If you quickly switch between these values you effectively get a square wave. Switch fast enough, put it through a speaker and we have sound.
That’s the basic principle of a Lunetta Synth. We use a logic chip for a different purpose. To create noise. You can find an excellent document on the subject here: Introduction to Lunetta CMOS Synths.
The NAND logic operation
Logic operations take one or more input and output a single value. Examples are AND, OR, NOR, XOR, NOT and NAND (Not AND) operations. These are quite simple operations that output their value based on a truth table. The example below is the NAND logic operation. Two inputs (A and B) are compared to get one output (Y).
|Input A||Input B||Output Y|
If one or both of the two inputs of the NAND operation is LOW the output is HIGH. As a result only if both inputs are HIGH the output is LOW.
This animation shows how this works with two input 5V square waves in a circuit.
The Quad NAND logic chip
The Quad NAND CMOS chip we use for this project is the CD4093. This chip contains four NAND logic gates with two inputs and one output each. It has a Schmitt Trigger action on the inputs. It handles noisy input signals so we get a clear HIGH or LOW states at the input. And this results in a clear output as well.
We connect pin 14 (Vdd) to a DC voltage source (5V works) and pin 7 (Vss) to ground. Pin 1 and 2 are input 1A and 1B resulting in output 1Y as follows.
So far so good. Next, we’re making an oscillator out of this chip.