A while ago, I decided that I wanted to build an analog modular synth. After doing some research, I found out that I didn't know all that much about analog audio electronics at all. So the best thing to do was to start from the very beginning and to build all kinds of simple oscillating circuits to get a grip on the basics.

When you google for simple oscillators, you inevitably come across the stepped tone generator aka the Atari Punk Console (APC). The circuit was first published in 1980 by Forrest M. Mims III and was later slightly altered and renamed Atari Punk Console by Kaustic Machines. They gave it that name because its sound resembles that of the old Atari video game consoles.

When I did build my first APC, I quickly discovered why it is so immensly popular. It is very cheap and easy to build and it produces a lot of weird and funky noises with very few parts.

The only thing that, imho, is missing in 90% of the available circuits online, is a way to add an external voltage control. It can be done by adding only two extra female Jack connectors to the two free pins on the 556 timer. WIth these two extra connectors, you can add an external oscillator, LFO,...

Step 1: What Do We Need for This Project?

A 556 dual timer
A 1K resistor
An LED of your choice
A resistor for the LED. In my case a 470Ohm
A 100nF and 10nF capacitor
A 10uF electrolytic capacitor
2 x 470K or 500K potentiometers
A 100K Logaritmic potentiometer or a 100K and 4K7 resistor
A switch
3 female jack connectors
A DC connector
A 9V powersource
A case. I used a plain and ready available project box. But google for Atari punk console and be amazed about all the weird and wonderful housings for this device. I am sure that you can come up with one of your own.

Step 2: The Circuit

The circuit is basically 99% the same as the original Forrest M. Mims III design, except for the 100K potentiometer that I added for volume controle. The LED and switch are optional.

For the voltage controlled bit, I just added a female jack to pin 3 and one to pin 11 of the 556 and that does the job.

Building the circuit is really easy and you should definately try to tweak it or to add your own bits. 556 ic's are really tough and can survive a lot of electronical abuse!

I added the eagle file of the board fot those who would like to use it. The board has 2 options for output: eIther a line level or a volumecontrol.

For line level: Add the 100K and 4.7K resistor and connect the rightmost pad and the centre pad of the potentiometer.
For a volume control: Add a 100K potmeter and connect directly from the 10uF capacitor to the rightmost pin of the potentiometer.