Extrinsic Motivation: An Open, Modular Effects Pedal

Microcontrollers and Arduinos are cool and all, but dealing only in the digital domain does have its limitations. In fact, most of your electron heroes didn’t begin their electronics career by blinking pins on digital outputs; they were solely in the analog domain with their radios and, yes, guitar effects pedals.

[Josh]’s entry for The Hackaday Prize was by far the most analog project of the entire contest. It’s an open source effects pedal that takes advantage of the modular design of the most popular pedals in history.

A good number of the famous circuits for turning an electric guitar into an aural experimentation are based on small circuit modules, packaged and repackaged again until the desired tone is achieved. [Josh] wants to pack these modules separately on different boards, specifically shields, although no Arduino is used, so any sound can be created.

Already [Josh] has done some research to determine what circuits and circuit modules to clone. The list should be fairly familiar to anyone with a pedalboard – Tube Screamers, Fuzz Faces, Big Muffs, and Phase 90s are at the top of the list. He may not get to the complicated digital effects like pitch shifters and digital delays, but it’s still a great project for experimentation.

You can see [Josh]’s project video below.

SpaceWrencherThis project is an official entry to The Hackaday Prize that sadly didn’t make the quarterfinal selection. It’s still a great project, and worthy of a Hackaday post on its own.

18 thoughts on “Extrinsic Motivation: An Open, Modular Effects Pedal

      1. And sound good, no one will pay anything if they don’t sound as good as the cheap clones you can already buy. I would think a module would have to be around the £10-20 mark. I think what alot of people would like, except the purists, is a digital pedal usb connected, that they can drag and drop blocks on a screen to create new sounds.

          1. My target audience is not electrically minded, but most people are not idiots either. So it has to be simple, cheap and (reasonably) fool-proof. The requirements are geared for this by requiring all controls to be panel mount, assembly by screw driver, and the ability to pick up all parts required to make a module at the local ‘Shack here in the States.

            The requirements are enclosure-independent. The only requirement is to leave a space to fit the modules and a flat surface for panel mount hardware. This gives complete artistic freedom to the user, as well as enabling use of standard 3ish knob boxes.

            @Al Bundy
            The Zvex pedal is really too expensive for what it does – the modules that I have scratched out on napkins should run <$1 each to manufacture on perfboard: most of them require little more than a few transistors or an op-amp, a couple of diodes, caps and resistors. 10 components on the high side.

            The requirements enable enough design freedom that you can scratch build the whole thing, or components can be purchased (whenever I actually get to that point). Truly the only way this can be successful is if a major retail store picks up the design, since only a handful of people would actually build these from scratch. There's quite a gap to get to the retail market…

    1. The downside of the Line 6 is that you are limited to what they make and you can only use one at a time. The point of my project is to allow freedom of experimentation without knowing about electronics.

  1. This reminds me alot of a project that a colleague recently launched. Peterson Goodwyn from DIYRecordingEquipment.com made the Colour. He calls it a modular harmonic saturator for use in the studio environment. It sounds like these two should start a dialogue!

  2. Thanks for all the links guys!

    The key philosophy for this design was to overcome the weaknesses of most of the mentioned pedals. The only way this can be done is to write extensive requirements first, totally forgetting about form. By starting out this way I was able to break out of some of the main limits of the other designs. These requirements can be found on my git wiki, and although it is mundane to read, you can see how it works by reading them. I design aircraft structure, and this is how we do it – define the requirements first, then only make a design that meets the requirements.

    Key features that are found in other designs that were thrown out:
    -Pre-configured physical interfaces (forces the user to own your box – no design freedom)
    -Cartridge – backplane design (forces a limited fx chain and also drives enclosure design)
    -complete pedal circuits on a single module (you can’t put a screamer tone stack in a big muff pi…)

  3. There is a similar module using the Spin FV-1, which was designed principally by the late great Keith Barr, formerly of Alesis:


    “The SKRM-C8 reverb and effects module line is an easy to integrate effects solution for your pedal, amp or other audio equipment. These modules are available pre-programmed and can be custom programmed for your product. Modules operate from 5V to 12V DC to ease integration into your design.”

    The FV-1 is neat because it’s got AD/DA converters on board, requires only sample clock, and while the limited 128 instructions per sample sound skimpy, the instructions are powerful enough to enable many interesting pitch shifting, delay, modulation, filtering and reverb applications. If you structure your algorithm right, you can get up to a second of delay memory out of it. Additionally, there’s a good amount of documentation to get people started, a bunch of source code to build on, and an active developer community.

  4. Personally, I don’t get the need for physical modules of any kind unless you’re being an audio purist. In college (circa 1992), I built a DSP system based around a 4MHz 8088 cpu. The bandwidth wasn’t great and the whole thing had to be done in assembly, but it proved it was possible to do it in software alone. With today’s hardware, this should be a walk in the park. It doesn’t have to be complicated and the end user wouldn’t need to be an expert to change/modify the effects. Any software module the community would create would simply be loaded onto the device to change the behavior.

    Maybe that doesn’t fit the requirements, but if I had the time on my hands, it’s an avenue worth looking at.

    1. The market is already moving towards individually downloadable DSP effects. This is a good example: http://www.eventide.com/AudioDivision/Products/StompBoxes/H9.aspx

      Interestingly, the market seems to think that pedals that store only one effect at a time must be higher quality than one that holds multiple effects. This stems from older multi effects where both ROM/RAM and processing power were extremely limited, and the designers wanted to cram as many effects on as possible, since it had little effect on product cost. Of course, these days ROM/RAM is not the limiting factor, only the processing power vs cost and the quality of the algorithms.

      The market does not, on the whole, accept digital boost/overdrive/distortion pedals, but does accept modulation pedals. It may be a while before this changes.

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