Atari Punk Effect - Guitar Distortion Based on Atari Punk Console

About Atari Punk Effect

Many people start their journey into sound electronics by building a simple synthesizer - the Atari Punk Console. This generates a square wave sound similar to Atari console games from the early 1980s.

As this is a simple circuit, I decided to modify the layout to use it as a guitar effect.

Sound and Pictures

Electronics

The electronic is quite simple. At first, an LM386 is used to amplifiy the incoming signal. This is done according to the schematics in the datasheet, so that the signal with a maximum of 1V coming from a guitar is scaled to a maximum of 9V to use it for triggering the two timers in the NE556.

Looking at the introduction to 555/556 timer, you can see, that the first timer is running in something similar to astable setup, while the second timer is running in a setup similar to monostable. Both timer take the amplified signal from LM386 at the trigger input.

First Timer (Pins 1-6)

Each time, the trigger input, e.g. the amplified signal from LM386, exceeds 6V (2/3 of 9V), the output is set to high (9V), until capacitor C2 is discharged. The output is then set to low (0V). VR1 controls the length of the high signal until a high signal is set to low.

Second Timer (Pins 8-13)

The output from the first timer is fed into the control input with VR3 controlling the volume of the signal. This then sets the value to exceed from the trigger input to set the output to high. Each time, the guitar signal exceeds 2/3 of the control input, output is set to high, until the capacitor C4 is discharged. Output is then reset to low. VR3 changes the duration until a high signal is set to low.

VR4 is used to control the volume of the effect, C5 is there to remove humming.

Where do all these odd values for the resistors come from? Those are resistors that I had lying around, different values will work as well.

Part List

U1

LM386

U2

NE556

C1

10µF elco

C2

100nF

C3

47µF elco

C4

10nF

C5

10µF elco

C6

4.7µF elco

R1

220Ω

R2

44kΩ

R3

1.2kΩ

R4

300kΩ

R5

20Ω

R6

47kΩ

VR1

470kΩ log

VR2

470kΩ log

VR3

100kΩ log

VR4

47kΩ lin