I have always loved guitar stomp boxes. Although there are probably no more than 15 or so generic guitar effect circuits out there, they come in a huge variety of flavours. The industry has a seemingly endless number of small boutique manufacturers and a handful of very large players with massive product lineups. This means that guitarists can choose between thousands of different effect pedals, and you would be hard pressed to find two guitarists with identical pedal boards.

Better yet, guitar stomp boxes are usually small and quite affordable, and the format is very DIY friendly. Most pedals use 9V DC switching power supplies that are cheap and widely available, and simple aluminium enclosures can be bought on the cheap and customised with consumer grade power tools.

Stomp box circuits are usually rather simple affairs and with a bit of practice, you can etch and solder your own circuit boards. There are plenty of free designs knocking around on various DIY internet forums, and plenty of DIYers are offering free advice and trouble shooting help if you need it. 

What’s Wrong with Stomp Boxes?

Stomp boxes are really cool and as a DIY friendly format for somewhat LoFi (guitar) effect devices they pretty much check all the boxes. So, what more could you ask for? 

Not much… if you’re a guitarist, that is. 

I happen to make electronic music, and the only instruments I play (badly) are synths and drum machines. My workflow is very much centred around my DAW but I often do run things through external effect units. I love the idea of using stomp boxes in my workflow but unfortunately I find they often don’t work that great for me.

There are a few reasons for this:

  • First of all, the frequency response of most stomp boxes are optimised for guitar. They tend to boost frequencies around 1.5 KHz and often cut the lows (sometimes the highs as well). This can work well for some things but it is not very versatile.
  • Guitar effects are designed for high impedance, low level instrument signals rather than +4 dBU audio interface inputs and outputs. This means you typically have to lower the volume of signals going into the effect significantly to avoid (unwanted) distortion at the input stage. Since stomp boxes tend to be rather noisy, you often get audible hiss when you boost the signal level back up again.
  • Most stomp boxes are mono, but my tracks often have stereo content. Running the left and right channels through a stomp box separately works but makes for a lousy workflow.
  • The stomp box form factor is all wrong for me. I don’t put my effects on the floor, connect them in series with patch cables and switch them in and out with my feet. I put them on my table and plug them into my patchbay, and I find that things quickly get messy if I set up more than a couple of stomp boxes at a time. I would much rather have my effects tucked away in a powered rack (or at least in table top enclosures) and wire them up to my patchbay permanently with normalled connections to my audio interface. That way all the effects would be ready to go at any time and I can keep my studio neat and tidy.

I really wish there was a format out there that had all the benefits of stomp boxes but was better suited for non-guitarist, DAW focused music producers like me. I have been thinking about this for some time now (years actually) and I finally decided to do something about it.

The Audio Brick Format

A few months ago I started working on a format that will allow me to build simple hardware audio devices (not just effects) that have all the benefits of stomp boxes but are optimized for hybrid, DAW centered workflows. 

Specifically, I set out to create a DIY friendly format that is simple and accessible, facilitates tight DAW integration and allows for easy adaptation of guitar effect circuits. I decided to call the format Audio Brick because the rectangular table top enclosures I use look a bit like bricks. They also stack really well, just like bricks (as opposed to stomp boxes).

No Hardware Controls

The toughest decision I made in the design process was to completely eliminate hardware controls on the physical units. Audio bricks have no knobs, switches, buttons or flashing LEDs and rely completely on digital control of the analog circuits. 

Hardware controls may be sexy, but they are not absolutely essential in a DAW centred workflow. Leaving them out makes the format so much more accessible and affordable because:

  • One enclosure fits all boards that follow the standard, and there is no need to create individual mechanical designs for each separate device. This makes it so much easier to realise new device designs since the mechanical design is usually a very large part of the work. For many DIYers, the mechanical design and fabrication is also the most difficult and tedious part of their projects.  Finally, the “one size fits all” approach means that enclosures can be sourced in larger quantities, and it is possible to have vendors customise enclosures with cutouts and silkscreening without breaking the bank.
  • Effect units without hardware controls can be placed out of the way in a simple rack enclosure with a blank front panel. Table top enclosures can be stacked neatly and do not have to be with reach for a fast workflow.
  • Potentiometers and switches can be expensive and take up valuable real estate on your circuit board. Sometimes you may need to add small panel mount or “piggyback” circuit boards to accommodate controls, which adds complexity and cost to the design.

As will become apparent in the following, there are actually plenty of good ways to integrate audio bricks without hardware controls into your studio or live setup, so this may not be as great a sacrifice as it seems.

Onboard Arduino

Audio bricks have an onboard Arduino for digital control of the analog circuits using USB MIDI. Any Arduino board can be used, as long as it will act as a class compliant MIDI device when connected to a USB host.

I use Pro Micro Arduinos from Sparkfun while breadboarding and incorporate a similar design directly in the circuit board at a later stage. I find the integrated single board approach more elegant, but you could just stick an off-the-shelf Arduino on your finished board instead and be done with it.

Apart from providing a MIDI interface, the Arduino controls digital potentiometers, switches and similar components that are used in place of hardware controls. The Arduino can also be used to provide control signals such as envelopes and LFOs in some circuits, which reduces both cost and complexity of devices.

Finally, both builders and users can program their devices with the simple and accessible Arduino editor and libraries.

Standardized Form Factor

Audio bricks are built on 100×160 mm eurocard sized circuit boards, the same size as the boards used for API 500 series modules. Instead of the gold fingers found on 500 series boards, audio bricks have connectors mounted directly on the back edge of the board. Components on the board can be up to 30 mm tall, which is enough for large connectors, capacitors and “piggyback” circuit boards.

The standard eurocard size makes it much easier (and cheaper) to source single unit table top enclosures. It also means that four boards can be mounted side by side in a 1U rack enclosure.

Inputs and Outputs

Since audio bricks have all connectors mounted directly on the circuit board, they do not require an enclosure to provide power and I/O in order to function.

Audio bricks have unbalanced stereo audio inputs and outputs on 6.35mm jacks. The Jacks are stacked, so there is room enough to mount all connectors on one of the short edges of the circuit board. 

Power is delivered through a 2.1mm barrel jack, the same kind that is found in most stomp boxes. Most of my designs use standard 9V DC center negative power supplies (just like stomp boxes) but higher voltages or even AC could be used if necessary.

Finally, audio bricks have a full size USB type B socket that is hooked up to the Arduino. This connector is used to control the device via USB MIDI and to program the Arduino.

DAW Plugin

As mentioned previously, Audio Brick settings are controlled with MIDI CC messages rather than hardware controls on the unit itself.

In order to provide tight DAW integration, dedicated DAW plugin (VST and AU) can be created for specific Audio Brick devices. These plugins work like dedicated editors for devices and their parameters are mapped to MIDI CC messages that are transmitted to the hardware unit whenever changes are made in the software. 

Not only does this mean that you have full control of your device from your DAW, the plugin also saves all device settings in your DAW session, and initialises the hardware whenever you open the session in your DAW again. You can also automate parameters, just like with any other DAW plugin, and MIDI CC messages will be transmitted to the hardware device in real time.

Finally, you can store your favorite patches on your computer for reuse in other DAW sessions, just as with any other plugin.

I use the excellent JUCE framework to create the DAW plugins and compile against the reverse engineered FST header files (all under the GPL3 license).

Why Not the 500 Series Format?

Unless you already own a 500 series chassis with room to spare, you need to fork out quite a lot of cash to get started. 

500 series enclosures are typically built for 8-11 mono effects and come with fancy regulated dual rail power supplies. This is great of course, except they often cost €1,000 or more a piece, and will only host 4 or 5 stereo effects. And since most of the devices I’m interested in building are somewhat LoFi anyway, I have little use for high end power supplies.

In comparison, you can get a guitar pedal power supply for €10, and a neatly machined and silk screened enclosure for a single stereo effect unit could probably be made available for less than €30 retail. That adds up to €160 for 4 stereo units, and you can get started for only €40 for your first unit.

If you go buy some plastic food containers in IKEA and use them as enclosures for your DIY projects, you could probably bring that cost down by 50% or more. Your audio bricks would still stack nicely but you might get issues with electromagnetic interference if you use non-metal enclosures.

Why not the Eurorack Format?

Eurorack power supplies and enclosures tend to be expensive as well, and again you would need to fork out a lot of cash to get started. Furthermore, the eurorack format is optimised for units that have lots of hardware controls and need large front panels. Not many eurorack enclosures can accommodate 160mm deep circuit boards, so each audio brick would take up around 35 HP. Also, all the connectors would have to be placed on the front panel, which is not ideal.

Incorporating Audio Bricks in Your Setup

Once I started thinking about alternatives to hardware controls on the unit itself, I realised that there are actually quite a few neat ways to incorporate Audio Bricks into both studio and Live setups.

If you are a NI Komplete Kontrol user, you can use the DAW plugin to map Audio Brick settings to the knobs on your keyboard automatically. The knobs will be neatly labelled with the proper names in the LED scribble strips on the Komplete Kontrol device. I’m sure the Nektar and Novation AutoMap devices can be used in similar ways, but I haven’t looked into that.

For live use, Audio Bricks can be controlled from software such as MainStage or Camelot Pro. And you can of course use any hardware controller you may have lying around to control Audio Brick device settings with knobs, sliders and buttons.

You could obviously set up any hardware MIDI controller to control your effect units (with or without MainStage or Camelot Pro), and if you feel very strongly about dedicated hardware controls and have the necessary skills, it would be fairly simple to DIY dedicated control boards for your hardware units.

What’s Next?

I have been working on this format for some time now, and I feel that everything is starting to fall into place. I have designed a protoboard with an onboard Arduino and connectors, so I can prototype and test designs quickly and this has really helped me move things along. 

I have quite a few ideas for devices I want to build for my own studio. I’m currently working on a design for a Fuzz effect inspired by the EHX Big Muff Pi, and I’m looking into designs based on the EHX Memory Man and the Boss CE2 as well. A stereo version of the Shruti synth from Mutable Instruments could also be an interesting project.

These initial projects will serve as proof of concept, and I will tweak the format along the way if necessary. Further down the road, I hope to set up a small business selling “boutique” audio bricks in small quantities, either as DIY kits or as fully assembled units.

In the meantime (and in the hope that others might find the format useful too) I’m making most of my work available as open source hardware and software on Github. 

If you have comments or questions, please leave a few words below. I’m curious to know what you think about the format, and if you have any ideas for improvements? Which designs do you think might work well as audio bricks? How would audio bricks fit into your live or studio setup and your workflow?