pi-Stomp! A Hi-Def Multi-FX Platform for Guitar

Quad-core raspberry pi based DIY hardware. Free Open source software. Infinitely expandable, configurable, controllable, enjoyable.

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treefallsound has 34 orders / 2reviews
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Note: Support will continue for this project but we've sold out of kits. DIY'ers are encouraged to check out pi-Stomp Core which is smaller and easier to customize:

Details, sound samples, build instructions and parts bundles all available at treefallsound dot com

pi-Stomp is high definition multi-effects stompbox platform. The recommended install contains over 350 plugins - effects, modeled amps and sound generators. It was designed for guitar and bass, but works great for processing electronic instruments as well.

Numerous virtual pedalboards containing a dozen or more simultaneous plugins, can be constructed via MOD, a super powerful yet easy to use drag-n-drop web user interface. Once your pedalboards are saved, only the pi Stomp is needed on-stage or in the studio.

Control it via the mappable footswitches & knobs or connect an expression pedal, MIDI controller, phone

Full details including videos and sound samples can be found at and the pi-Stomp wiki

Quick overview

pi-Stomp is a DIY platform for guitar, bass and keyboard processing.

The heart of the software is the open source MOD host/ui created by which allows you to create virtual pedalboards with up to ten or more simultaneous plugins.

Check out some sample pedalboards hear what they sound like here

Purchase the parts using our provided Bill of Materials. The total will be about $198 plus applicable tax and shipping.  It does require at least intermediate soldering skills.  But we've done our darndest to make it as easy as possible.  You will be rewarded with a very powerful multi-fx platform that rivals many commercially available units (HX Stomp, Headrush, etc.).  Better than those though, You built it.  You can upgrade or modify the hardware.  You can install whatever software/effects you want.  If it runs on Linux, it'll likely run on pi-Stomp.



Since you're reading this, you're likely a maker/hacker and a musician.  You love to build and create.  So what could be better than making awesome music using hardware (and maybe even software) that you built?  That's been my dream for decades (read "experienced", not "old" ;-).  Raspberry Pi and high def sound cards along with some open source software like LV2 (plugin format) and MOD/MODEP, have finally made such an endeavor possible.

The project started in Spring 2019.  Although I had working prototypes within a few months, creating something that others can build is a lot of work.  The industrial/mechanical design along with documentation has actually required way more effort than the electrical and software design.  The latest circuit board is the 8th iteration.  The last two public versions have been built successfully 12+ times by builders around the world.  So this is a fairly mature project which I will continue to improve.  Your help and ideas are more than welcome!

Hardware Specifications

  • Raspberry Pi 1.4 Ghz 64-bit quad-core processor
  • Dual ins/outs, 24-bit, 48 to 96kHz stereo audio
  • Input Impedance: 1 Meg Ohm
  • Latency: 2.67ms (128 frames/96kHz).  5.33ms if CPU load is reduced by changing sample rate to 48kHz or frames to 256.
  • Three rugged click-less footswitches with LED halos (assignable per pedalboard)
  • True bypass via latching relays
  • MIDI control via 5-pin DIN (old style) input connector or USB
  • Assignable Expression Pedal input and "Tweak" knob
  • 2 encoders for menu navigation and control
  • Output Volume control
  • 128x64 backlit LCD
  • Rugged custom aluminum powdercoated enclosure with UV printed graphics

Controlling pi-Stomp

pi-Stomp offers powerful and very flexible control via the onboard knobs and footswitches, but you can also control it externally to enable/disable specific effects, control wah, pitch-shift and any parameter of any plugin.  All controllers (including the onboard) simply send a MIDI CC message.  Each unique messages can be mapped (per pedalboard) to control whatever you want it to.


If you made it this far and still want to learn more, just visit the wiki.  Thanks for your interest!

  • Alternative Software running on pi-Stomp!

    Rand Reichenbach01/27/2021 at 23:21 3 comments

    pi-Stomp has always intended to be a platform. One of its main advantages over commercial units, is that it runs Linux, and thus can run additional software.

    Last week I made a firmware change to allow the hardware to work independently of the recommended MOD software.  So now, you can use pi-Stomp hardware with other audio hosts!

    You can even MIDI-map the pi-Stomp controls and footswitches to control effect parameters in the host.

    I’ve tested two such hosts so far. They both work great.

    Rakarrack – an awesome (Free) guitar oriented virtual pedalboard (shown here running on pi-Stomp with the display shown via realVnc)

    Carla – a Free, full featured modular audio host. It supports multiple plugin formats including LADSPA, DSSI, LV2, VST2, VST3 and AU, plus SF2 and SFZ sound font files!

    For more details and installation instructions, check out the Wiki Page

  • v1.0.2

    Rand Reichenbach11/16/2020 at 21:59 0 comments

    October 24, 2020

    New batch of boards available.  v1.0.2 with improvements based on feedback from the first 4 builders.

  • Proof of Concept thru v1.0.1 Release

    Rand Reichenbach11/16/2020 at 21:57 0 comments

    September 11, 2020 - Went public went live.  "Advertised" on two forums: &

    September 2, 2020 - Enclosures!

    Feb thru August, 2020 - Covid Months
    Did some redesign of the relay bypass.  Otherwise kindof stuck without a source for enclosure manufacturing.  Focused on software improvements.  Got friends to build units and give feedback.

    February 22, 2020 - pi-Stomp Build #2 with enclosure

    • Swapped location of Left and Right jacks (more intuitive)
    • Improved signal routing to minimize noise

    August 25, 2109 - First PCB Version

    These functions working:

    • Audio processed thru both Left and Right channels
    • Headphone output works
    • Bypass reed relays controllable via footswitch
    • LCD shows current Pedalboard / Preset / Tweak param / Tweak value / footswitch mappings and enable state
    • Each footswitch sends MIDI CC and toggles LED ring
    • Tweak Knob sends MIDI CC and changes corresponding parameter when mapped. Display graph shows value.
    • DIN and USB MIDI input produces MIDI CC and changes param
    • Expression pedal input produces MIDI CC and changes param
    • Top Encoder changes Pedalboard. Future software change necessary to change Preset.

    May 8, 2019 - Mod a'la pi

    4 knob, 2 footswitch.  Stripboard.  16 position encoder selects MOD pedalboard/preset. 

    Arduino for sending MIDI CC to pi via USB with input from two assignable tweak knobs, expression pedal and DIN MIDI jack.

    (shown without pi installed into 2x20 header)

    April 5, 2019 - Proof of concept

    Raspberry pi running Mod software Audio card hat LCD hat (displaying Pedalboard name and list of mapped parameters)

    Preamp for guitar input Arduino controller sending MIDI CC via USB with input from a tweak knob, DIN MIDI, and an encoder for program (pedalboard) change

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Enjoy this project?



AVR wrote 11/25/2020 at 07:22 point

Latency compared to commercial solutions ?

  Are you sure? yes | no

Rand Reichenbach wrote 11/26/2020 at 06:14 point

You may know that latency for a DAC/ADC is more a function of the sample rate and frames/buffer size than the electronics it passes thru. 

For pi-Stomp, you can change the latency to be low as 1.3ms to 11ms or more depending on what you choose for your sample-rate and frame size.  The 1.3ms (96kHz/128 frames) will not likely perform well except for very small/simple pedalboards (3 plugins maybe).  I find that 96kHz/128=2.67ms is a better choice to support more plugins (6 to 8).  96kHz/256 or 48kHz/128=5.33ms is better for larger pedalboards or ones with lots of simulator (amp/cab models, pitch shift, etc.) plugins.

If you want to see actual pi-Stomp latency (which is generally very close to theoretical), I've posted that (with oscilloscope plots!) here:

Regarding how that compares with commercial devices.  I'm not certain of the number of frames that various devices use but I do know that Line6 HX stomp runs at 96kHz and I can't imagine it uses less than 128 frames.  In that case, it would have a theoretical latency of 2.67ms.  Mod Duo runs at 48kHz, so I'd expect it's latency to be 5.33ms.  Those are the main "competition" so I'd say pi-Stomp is in good company.  Personally, I don't really notice 5.3ms.  10.6ms I do.

  Are you sure? yes | no

Rand Reichenbach wrote 11/23/2020 at 04:59 point

Thanks for the kind words and interest, Craig.

To your questions...  Full size pi?  Guessing you mean the "B" models?  Those would require a bigger enclosure, and for what advantage?  Extra USB ports?  You certainly could though.  It works just fine.

Regarding XLR, you could feed your mic to an XLR preamp or direct-box then to the pi-Stomp.  XLR on-board the pi-Stomp would require an additional preamp - current one is unbalanced with unity gain.  Here's a XLR input module with almost all the bells and whistles:

it or something like it could be wired in place of one of the existing 1/4" TS jacks and should feed just fine into the unity buffer.  Phantom power would require a boost converter or additional supply.

Regarding more footswitches/knobs, sure, natural thing to want.  I went with 3 footswitches because you can always add more by connecting any midi-controller to the DIN midi or USB ports (demo of that:  FWIW, I've started prototyping an extension box that would add at least 2 footswitches, maybe some knobs, and *maybe* a small display to show the mapping of each control.  Once I sell out of pi-Stomp bundles (20 or so more to go), I'll likely start on a smaller/cheaper version with reduced functionality, but still expandable via USB/MIDI.  If you would like to give suggestions on either project or collaborate, I'm all ears.  If you want to create your own pi-Stomp XL/XLR, I could likely help you there.  There's currently only one unused GPIO pin, but there are 4 unused Analog over SPI channels which could be used for pots, footswitches, etc.   Technically, you could use the pi-Stomp PCB as is, but you'd have to hack on some analog input wires.  More ideally, a new PCB rev with a new header could allow easy connection.

  Are you sure? yes | no

Craig Hissett wrote 11/29/2020 at 22:39 point

Thanks for your reply buddy!

My thoughts of using a full size pi was more to get the power and ram of a Pi4 board in there :-)

I love the idea of a smaller unit, maybe something simple with the main I/O, a single button and a screen, then the user is able to pair it with any combination of expansion boards to give them the necessary input.

I'd personally love to build a similar simple module with the Pi4 and it's 4 usb ports, then use perhaps two microcontroller powered expansion boards for the footswitches via usb.

  Are you sure? yes | no

Craig Hissett wrote 11/22/2020 at 21:21 point

Hey man, as you know already I think this is absolutely amazing. I will hopefully get a kit when I can afford to pick one up.

In the pics it looks like a model A+ - have you any plans of making them to fit the fill size pi?

  Are you sure? yes | no

Craig Hissett wrote 11/22/2020 at 21:54 point

Im also intrigued by your proof of concept too; I am a trombone player by trade, and would love to work on a version of this pedal with an XLR Input, to take my trombone mic.

If love to know more about how you worked through your concept model and try coming up with a bigger board with a few more buttons and that XLR in 😎

  Are you sure? yes | no

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