The Beast

Status: Completed
Dates: December 2006

Overview

Junior year at Calvin College I was assigned a team project. The goal of the project was to design a simple yet useful analog circuit. Not only design, but also fabricate a printed circuit board and create a prototype. The team decided a guitar effects pedal would make for a fantastic project. The project was deemed The Beast.

After doing some research the team discovered a few useful overdrive distortion guitar effects schematics online. The designs were studied, tested, and modified. We eventually ended up with the schematic shown below.

Schematic

Now, to test my memory. The overdrive effects pedal design utilizes two op-amps to create it's unique sound. The first op-amp, IC1, is the distortion gain stage. Two different types of clipping are designed into the circuit. Diodes D1 and D2 produce a soft clipping distortion, while D3 and D4 create a hard clipping distortion. As the gain is cranked up using potentiometer, R7, the distortion becomes more pronounced. A durable dual-pole dual-throw footswitch was used in the prototype to switch between the two different clipping modes. The second op-amp, IC2, is only present to provide the effects pedal with an adjustable output. A 9 volt battery was used to power the prototype, connected to TP6 and TP5. A design feature not shown in the schematic is true bypass. A foot switch was used to completely bypass the effects circuit and directly connect the guitar input with the effect pedal output.

Pictures

Unlike IRLink I actually managed to find some pictures of the prototype.

A general overview of the mess of wires, circuits, and controls that is The Beast.

In case you wanted a closer look, here you go.

The custom PCB created in Eagle, fabricated at Calvin College. Notice all the terribly thin traces. Hey, we didn't know any better at the time. We etched about 5 boards and only 2 had zero defects. Live and learn. It was also a lot of fun drilling all those holes manually.

I managed to find the Eagle schematic file for this project. I tried to clean it up a bit. At some point in the future I may revisit this project and redesign it.