My Modular Synth Plan - Format

A crucial element in planning my modular synth is the format. If you're familiar with modular synths, you'll most likely be familiar with Eurorack, which is currently the standard modular synth format available. However, there are many alternative formats out there, and sport some unique features. In this post, I hope to provide a bit of an overview of the modular synth formats out there, and the format I plan to move forward with for my DIY modular synth project.

So what do I want in my synth format? A few design features I want to consider for my modular synth format are;

• Relatively compact panel sizes, but with enough space for tactile controls;

• Simple dimensions which allow for easy DIY fabrication;

• Options for compact utility modules;

• Jack layouts that minimise wires going across modules;

• A standard power supply.

Most (if not all) commercially available modular formats are designed to conform with standard rack units. One rack unit (1U) is 1 3⁄4 inches or 44.45 mm. The widths of modules is generally measured in hp, short for horizontal pitch. One hp is 0.2', or 0.508mm.

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The Formats

The current standard format for modular synths is Eurorack. Doepfer introduced their A-100 modular system in 1995 which first utilised a 3U module height, and since then, has become the most common available modular format.

Some Eurorack modular systems also utilise smaller 1U tiles. These tiles usually perform utility functions, allowing more space in the 3U system for other modules. Intelligel's 1U modules are likely the most common example of these. Alternatively, some Eurorack modules aim to minimise real estate by packing maximum functionality into a narrow footprint. I prefer the former approach, where utility modules can be kept separate from the core module and may be an approach I include in my design.

Some other standard Eurorack (3U) design features include;

• 3.5mm jacks

• +/- 12V power supply

• Standardised "hp" widths.

Ambient Artist Ann Annie's setup is an example of a smaller "skiff" Eurorack setup.

Augustin Fievet's Eurorack setup here is housed in an Intelligel case, and utilised a row of 1U Intelligel modules.

The another common format is the 5U format adopted by Moog. These modules were amongst the first fully modular systems made in the 60s. This larger format allows for larger 1/4' jacks to be utilised, and the control interface of the modules to be more user friendly, due to larger and spread out controls. Because of these features, it could be argued that this format is both more durable and more suited toward performance. Modules generally have the dimensions of 8.75" by 2.125".

Originally, Moog introduced power supplies which produce assymetrical voltages (-6v and +12). This was replaced in later units with +/- 15V power supplies and this has remained standard.

Standard Moog-style format (5U) features include;

• 1/4' jacks

• +/- 15V power supply

• Standard 2.125" Width

A demo by Look Mum No Computer of a Moog System 55 modular synth

The 4U modular format, as utilised by Buchla and Serge. Buchla, along with Moog, were pioneers in modular synthesis, however have remained a niche format which sought to push the boundaries of modular synthesis . Contrary to Moog's fairly traditional approach to synthesis, Buchla instead focused on creating experimental modules, which together create unique soundscapes. In doing this, Buchla innovated techniques which are common today, such as generative sound. The 4U modular format modules generally feature dimensions of 7' by 4.25'. Banana jacks are utilised, as well as standard 3.5mm audio jacks.

Standard Buchla format (4U) features include;

• 3.5mm & Banana jacks

• +/- 15V power supply

• Typical widths are 84 and 104 HP

A demonstration of a small Buchla system.

Over the past few years, I have become a big fan of Look Mum No Computer, and the modular system which he has built. Sam is not only a hugely talented musician and entertaining performer, but also does an incredible job making modular synth more accessible to those new to the world.

In the interest of simplifying dimensions to be more DIY friendly, and suit his performance style, he adopted his unique "KOSMO" format. This combines many of the features of Eurorack and 5U, including 1/4' Jacks and +/-12V power. However, the dimensions move away from the standard Rack Unit heights and hp widths, and instead opt for standard metric units - a standard 200mm height and generally a 100mm width (depending on the module).

Standard KOSMO format (200mm) features include;

• 1/4" jacks

• +/- 12V power supply

• Typical widths are 100mm

A walkthrough of Look Mum No Computer's KOSMO DIY modular synth.

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My Format

Taking into account the features I like about each of these formats, I've decided to adapt these into a unique format that will better fulfil what I want from my modular synth. I have chosen to design my modules outside the rack unit convention, and instead, adopt sizes which are easier to DIY, similar to LMNC's Kosmo format. However, instead of the 200mm height of the Kosmo format, I want to adopt a 150mm height for regular modules, and widths which are multiples of 25mm.

In addition to these standard modules, I've chosen to also include smaller "mini" modules. These will be used for utility modules, similar to how some 1U modules are adopted in some modular systems. These modules will be used mostly for modules with minimal or no controls (ie. multiples, MIDI interfaces, logic gates, simple VCAs, simple envelopes etc.), to ensure my synth cases can have maximum functionality with minimal real estate.

These dimensions are larger than the standard 3U and 1U dimensions of eurorack, and hopefully mean that the usability of the modules will be better. I won't design anything with TINY knobs, like are sometimes found on some eurorack modules, but will also not feature large controls like that found on the 5U or Kosmo modules. As I plan to use this modular system more for studio-use and less for live performance, I see this as a necessary tradeoff for a compact design.

In terms of power, I plan to adopt a standard Eurorack +/-12V power supply. I plan to utilise 2x5 box connectors for power connections, as is standard in many Eurorack modules. No 5V power will be distributed from the power supply and power will be regulated on individual modules where 5V is required.

The picture below shows some blanks I made to demonstrate some of the possible sizes of modules for both the regular (150mm) and smaller (75mm) heights.

Blanks of possible module sizes

Now its time to build a case. Watch this space for updates!!!