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Factory Fuzz Guitar Pedal Circuit Simulation

If you'd like to jump straight to the interactive circuit simulator you can find it here:

Note: the simulator is best viewed on a large screen

Musikding Germanium Fuzz Guitar Pedal Kit

The Musikding Germanium Fuzz Guitar Pedal Kit is based on the famous Fuzz Factory circuit. After building the kit I thought it would be interesting to see how the circuit actually works. From analysing the schematic, the basic flow through the gain stages is relatively easy to follow but it's difficult to imagine how the clean input signal from the guitar gets transformed into the square wave output signal which creates the fuzz sound.

Electronic Circuit Simulator

The Electronic Circuit Simulator from (source code) is a web based circuit simulator derived from an original project from When a circuit is modelled and run in the simulator, it shows a visual animation of the electric current flow. Virtual oscilloscopes can also be added to observe the behaviour of the circuit.

Creating the Simulation

The schematic for The Factory fuzz pedal kit is available from the Musikding website as part of the set of build documents for the kit.

Musikding Die Factory Schematic
Musikding Die Factory Schematic

Modelling the circuit in the simulator is a matter of working through the schematic, component by component, making sure to connect everything correctly. The web editor allows you to export circuit model as text (source model) so that you can save and re-import it later.

Oscilloscopes were added to the input and output signals, the resulting chart is shown at the bottom of the editor. The green sine wave is the input signal and the red asymmetric square wave is the output signal. When running in the simulator, the animation shows the current flow flipping between the output stage transistors as the square wave changes from high to low.

This asymmetric square wave is what gives the fuzz circuit it's distinctive sound. This is similar to the charts that others have created from analysing the fuzz face circuit.

The potentiometers are labeled in the simulation as they are on the pedal: Vol, Gate, Comp, Drive, Stab. Their values can be adjusted using the sliders on the right hand side of the simulator and the changes can be observed in the scope charts in real-time.

Fuzz Guitar Pedal Simulation
Fuzz Guitar Pedal Simulation

As with any model, this simulation propably isn't 100% accurate, however it's output does seem to be a reasonable representation.

The interactive circuit simulator is best viewed on larger screen devices, i.e. laptop, desktop monitor:

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