An Introduction: How NOT to Build a Guitar Pedal

After nearly a year in development, the Cranberry Fuzz pedal is one round of enclosure mock-ups away from production. In the Rare Buzz studio, there are enough circuit boards, parts, and paraphernalia to build fifty of my first design. The journey has been a tough one – those of you that have followed our social media have been along for the ride. I thought I’d share some of the highlight reel to prevent other builders from making the same mistakes (really all part of the learning curve, I suppose).

For the first installment, I wanted to talk about the process of getting the guts together – namely, circuit design, circuit board design, and offboard wiring layout. Before I get a sea of hate mail, let me start by saying that my advice here may not apply to you. Everyone has their own tastes when it comes to design and manufacture. This is also geared toward the builder who plans to make small- to mid-sized production runs of their pedals – at Rare Buzz we are doing runs of thirty to fifty for our current and upcoming designs. If I was building single pedals to order, or if I was building these by the thousands, I would most certainly do things differently. With that caveat, here we go!

Breadboarding (March '18)

Friends, breadboarding is something that I consider to be a necessary evil. After this adventure, I believe that even more. This is probably the first of many times I will say this about something, but the closer you get the breadboarded circuit to what the production circuit will be, the better off you are. This means using the same parts and basic layout you will use in production – the entire circuit, including switching and off board components, if possible. There are some methods of non-mechanical switching that require buffering and biasing and this can affect the sound path. Fortunately for me, the Cranberry circuit uses mechanical switching via a 3PDT stomp switch.

Just as an aside, my obsessive nature dictates standard wire colors. I use red for +V, black for GND, blue for input, and green for output (blue plus the signal, get it?).

Perfboard (March '18)

To those builders out there who do boutique production and/or one-off pedal work in perfboard, I salute you. I think it is absolutely dreadful to work with, and going forward I will likely not be using it in any capacity. Please don’t let me discourage you from at least trying – there is certainly an art to it, particularly the type without rails like the veroboard I used. It’s just not for me. I should also note that I have not printed or etched my own circuit boards. Everything you will see going forward was produced by a specialty manufacturer.

This early version of the circuit had LED clipping on the input which really did nothing to help the sound.

Printed Circuit Boards

The next few steps in the process for circuit design, up to and including the final production Cranberry are built on printed circuit boards. There’s a lot to be said for PCB design, and that is a topic for another post or series of posts. My comments in this post will be limited to issues I ran into with physical layout of the boards and components and the resulting assembly process.

First Prototype (May '18)

In May, I ordered the first set of prototype circuit boards for the design that would become the Cranberry. At this point in the design process, the pedal would have switchable voicing in the second transistor stage – a feature that did not make it to production. This board came from the first round of designs I had manufactured that included some errors that made assembly extremely difficult. If you look at C7 (upper right corner), you can see the pads are extremely close together. I used the wrong package type here. C5 is too close to R7 (lower left corner) – another package failure. These boards were never populated because I caught these errors while building another design.

Most of the lower portion of this board was dedicated to clickless relay true bypass switching, another feature that did not make it to production.

Second Prototype (August '18)

The summer months are the busiest at the day job, so I wasn’t able to dedicate as much time to the design process. The second prototype boards came in early August. The package issues from May were corrected, and the switchable voicing and relay switching were eliminated. At this point, I replaced the first transistor stage with an op-amp based gain stage for some reason. I tried this on the breadboard (after I had these boards made) and was not happy with the results. Again, breadboard what you plan to circuit board.

The first two circuit boards used 9mm PCB mounted potentiometers. There’s not a problem with this, but the designs I made did not leave enough room at the top of the enclosure for the input/output jacks and the DC jack. I’ll cover this more when I talk about the enclosures and off board wiring.

Final Prototype (September '18)

September brought the final prototype circuit board for the Cranberry. At this point, the design choice had been made to use the MPQ2484 transistor on chip integrated circuit replacing the three BJT transistors that make up the two gain stages in the Cranberry. These boards were also updated to use the ECQ-series capacitors from Panasonic, which are unfortunately only available in the surplus market. If long-term production is a concern of yours, I would not use surplus-only parts since supply will become an issue going forward.

This board is used in the Cranberry P1 and P2. P1 has the following errors – when the first gain stage is turned all the way down, it cuts the signal, and the tone potentiometer is backwards. Both of these were fixed off-board in P2 and on the final production circuit.

Production (October '18)

Finally! The production circuit boards, courtesy of OSH Park. This is the board for Cranberry #001, waiting for its enclosure to arrive. These are a pleasure to solder – kudos to the folks at OSH Park. I did square up the board layout – OSH Park charges by the overall dimension of the board so the cost would have been more to include the tab. The only note I have about this design is that it is much easier to install the four wires prior to soldering the tone potentiometer to the board.

If I had it to do over again, I would have used Steve Demedash’s 555-timer based switching and kept everything on the board. Building these in quantity, I personally feel that the fewer off board connections the better – for me, this cuts down final assembly time. Open up a Boss or even a Keeley pedal, and nearly every component is on the board.

TL;DR Summary

This post is fairly long, I know. Here are the main points to take away when it comes to circuit board design:

  • Breadboard first. Breadboard as close to the final design as possible, ideally the completed pedal.
  • I don’t like perfboard, but other builders do. Try it a few times to see what you think.
  • Be aware of the physical dimensions of the components you plan to use. Use the appropriate package in your CAD software.
  • Be aware of how the board will sit in the enclosure, particularly its position related to off board components (more on this later).
  • Check and double check the orientation of your potentiometers – does turning the knob have the expected effect on the signal?
  • Be careful using surplus parts if long term production is a concern.
  • Off board wiring sucks. Design to minimize this – our goal at Rare Buzz is to be down to three off board connections in future designs.

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