Designing and Building a Peppermint Tin Fuzz Guitar Pedal
This is a custom guitar pedal that I designed and built, although describing it as "designed" might be a stretch, it's basically a Bazz Fuzz circuit with some changes and additions.
A base kit was purchased from Musikding which includes all the off-board parts you need to build a guitar pedal; audio jacks, foot switch, LED with bezel & DC power jack.
I didn't want to build a straight Bazz Fuzz, I wanted to experiment and build something a little different. After studying other circuits I ordered a bunch of parts; transistors, diodes, capacitors, resistors, pots and some stripboard.
Modelling the Circuit
A great way to learn and understand what is happening inside a circuit is to model it in LTspice. You can model an existing circuit and then experiment by adding, removing & changing components to see how the output signal is affected.
The Bazz Fuzz v2 is a simple circuit which uses a MPSA13 Darlington transistor. This creates a direct and heavy fuzz tone, which sounds pretty good considering how few parts are used. I was hoping to create something more subtle with a bit more character.
It was a interative process; modelling and prototyping various circuit configurations, experimenting with different capacitor values, different types of diodes and diode configurations, adding and changing resistor values etc. Once I could see and interesting change in the shape of the output signal in LTspice, I would build it on the breadboard and listen to how it sounded, eventually arriving at the following:
For comparison, here is the original Bazz Fuzz v2 schematic and plot which has a more pronounced square wave:
Designing the Circuit Board Layout
There are software applications to help with creating stripboard layouts but this is a relatively simple circuit so it was easy to sketch it out with pencil and paper. A craft knife was used to split a few of the copper strips (x's on the sketch), allowing a smaller board to be used.
Sockets were used for some components; input capacitor, clipping diode & transistor, so they can be swapped out later if required.
Preparing the Enclosure
Altoid tins are quite versatile due to their compact size, with many people finding creative uses for them. I had one lying around and decided to use it as an enclosure for this pedal.
As some components are mounted in the base and some in the lid, the layout took a bit of planning to ensure everything would fit together when the tin was closed. This wasn't too difficult as the circuit board is small.
The tin is reasonably rigid but care is needed with the step drill-bit to avoid warping or tearing the metal. There isn't quite enough height below the lid for the audio jacks so a notch had to be drilled from these too, some careful filing was also required to accommodate the washer and nut.
A couple of strips of duct tape were put on the inside of the tin to avoid shorting on the base of the circuit board.
Assembling the Pedal
The wiring of the off-board components was done with the lid open so I had to consider how the wires would fold when the tin was closed.
The End Result
This was a really fun and satisfying project. The pedal sounds great, it's responsive to guitar volume and pick attack so it can produce a nice variety of tones.