Tube like distortion in analog solid state guitar pedals

Design team members: Wayne Pau

Supervisor: Eric Kubica


Most of the music we listen to today is amplified in some format. For example, when we hear a guitar at a concert, it is usually plugged into a guitar amplifier. Inside the guitar amplifier, a process is used to take the sounds generated by the strings and make it loud enough to be heard by all those in the audience. In the past, a certain device called the vacuum tube was used as the amplification device in these guitar amplifiers.

As electronics advanced in the following years, so did guitar amplifiers. Soon, vacuum tubes were replaced by newer solid state electronics such as transistors. The only problem was that the new transistors did not have the same audio quality as the vacuum tubes. During their use, musicians became particularly fond of certain characteristics of vacuum tubes, especially when the tubes were overloaded, causing a pleasant introduction of harmonics and sustain called "distortion".

The goal of many of audio engineers and designers today is to be able to recreate vintage tube-like sounding equipment with newer transistor technology. One such device that exists today is the guitar distortion pedal. This device, in which a guitar can be plugged into, takes a guitar signal and alters it to make it sound as if it has been amplified by a vacuum tube based amplifier.

Project description

In this project, an attempt will be made to find and evaluate different methods currently being implemented to re-create tube-like distortion in guitar pedals, and to see which methods provide the best results. Both a qualitative analysis (human based audio test) and a quantitative analysis (harmonic, waveform and wave response analysis) will be done on a variety of different pedal designs. Lastly, since these end devices will be aimed at musicians such as guitar players, a survey will be used to gather information on what criteria are important to end users. The different pedals and circuit designs will then be evaluated based upon the information collected. The goal of this project is to present which designs of pedals successfully recreates the tube like sound, while meeting the needs of the musician.

Design methodology

The approach taken by this project is threefold;

1. Analyzing current market pedals: Four very popular distortion pedals (Dallas Arbiter Fuzz Face, ElectroHarmonix Big Muff, Ibanez TubeScreamer and Boss Super Overdrive) will be analyzed thoroughly. These pedals were picked because of their extreme desirability and large following among guitar players.

2. Analyzing circuit designs of guitar pedals: Three basics types of distortion circuit designs will analyzed, overloading transistors, hard clipping (shunted diodes in output path) and soft clipping (shunted diodes in feedback path of amplifier).

3. Vigorous testing of specially made test pedals: A few circuit designs will be created from the above research. Afterwards, the designs will be built and thoroughly tested to see how accurately they reproduce the favoured tube like sounds.

After the test results of the specifically designed test pedals, the various manners in which tube-like distortion can be generated through the use of analog circuits will be evaluated. The various methods will be rated on how accurately they recreate the vintage tube-like sound and how well they meet the needs of guitar players.