Guitar Pedals

In this work session, we worked on soldering the npn darlington transistor (KSP13TA) and 100k potentiometer to the circuit board. While soldering the pot proved to be a success, an error was made in correctly attaching the transistor. Through testing done with an oscilloscope, we were able to find another error: wires were soldered to the wrong set of pins on the audio jacks. However, it was not until another look was taken at the circuit diagram in KiCAD that we were finally able to determine the emitter, base, and collector on the transistor were in the wrong places. Once these pins were re-routed, we finally got a working pedal that produces a beautiful fuzzy tone. One observation we've made is that the fuzz effect is strongest when played on the bass strings. When the treble strings are struck, the fuzz is noticeably weaker. This is something we should try to address in the next iteration. The gating may actually be caused by the resistor's value.

After completing a PCB design for the simple pedal in KiCAD, we had it printed. In the lab, we soldered some of the components to the PCB like the diode, battery connector, capacitors and audio jacks. This was good practice as I'd never soldered on a PCB before. We also went over the difference between film capacitors and electrolytic capacitors that tend to be polarized and learned how they "filter" signals. As of now, we are waiting for the transistor and pot to come in so we can test the mini pedal.

Progress as of 1/29/2025

Instead of jumping straight into building a crazy fuzz pedal with different tone knobs and a volume knob using a bunch of transistors and resistors, we decided to start off with a simpler version to test out our components. This version uses a single transistor, resistor, diode, and two capacitors. With this smaller-scale version of the fuzz pedal, it's a lot simpler for us to understand how all the electrical components work. Now we understand:

-Transistors take the guitar's signal and amplify it, adding distortion at the same time

-The transistor’s hFe value (amplification factor) determines the degree of distortion. Higher hFe values lead to more distortion.

-Diodes clip the signal giving it the characteristic fuzz sound

-Resistors control the current and determine the voltage levels which also affects sound

-Capacitors filter the signal also affecting the tone formation or specifically the pitch Higher values result in a brighter sound, while lower values produce a warmer sound

This is basically everything we’ve experimented with and learned so far

We are currently working with kiCAD to design a schematic and PCB for the simple pedal