Preamplifier Subsystem

A project log for The Guitar Pedal Project: Multi-Effect Processor

A guitar multi-effect stompbox that allows musicians to create new and never-before-seen effect creations using their mobile phone.

ben-jacobsBen Jacobs 05/18/2020 at 03:410 Comments


The Preamplifier Subsystem is, in practice, actually a buffer circuit. It was originally designed to boost the incoming electric guitar signal to line level, but it was found that the WM8731 Audio Codec had a sufficiently high-quality preamplifier built in. Thus, all that was needed was a buffer circuit, to mitigate impedance differences between the Audio Codec input and the electric guitar pickups. A buffer circuit does not amplify a signal, but it prevents the input signal from being overloaded by isolating it from the output (the load). This is accomplished using an OPAMP with unity gain.

Schematic Diagram

Below is a schematic diagram for the preamp/buffer circuit being used. It was designed by team member Ryan Knepel, and serves as a buffer between the electric guitar output and the guitar pedal input.

In the schematic above, take note of the following components and their purposes:


The physical implementation of the preamp circuit was built using perforated PCB material and through hole components. A strip-board layout image may be found below: