Slightly Nasty is an Adelaide-based audio electronics company that specialises in modular synthesiser components for the 4U “Loudest Warning” format.


The Slightly Nasty range of synth modules grew out of my desire to expand the modular side of my own music studio, but not really liking the form factor of Eurorack. While playing around with my own ideas for an individual-module 4U/banana modular, I came across Charlie Kerr’s website and found that his Loudest Warning format was almost exactly what I’d been thinking about, only more fully fleshed out and with growing interest from a number of other builders.

Looking around at other 4U builds, I was struck by how so many of the modules out there were still using very old-school construction techniques compared to the maturing Eurorack market. They were generally just arbitrarily sized single boards, maybe with a couple of screw mounting holes, and wires soldered directly onto the PCB flying off to panel-mounted pots and switches. Having built these sort of things in the past, I’d always found them time-consuming and tedious, taking away way too much of the limited time I had to actually make music.

The other thing that struck me was that a lot of the designs were clones or remakes of fairly old designs, and often used component selections that might have been perfectly normal in the 1970s, but to the modern builder meant hunting down rare and overpriced parts – despite the fact that cheap modern alternatives could easily fulfil the same roles.

Finally, as someone who’d been working with synths and studio equipment for quite a while, I’d developed my own tastes and preferences for what I wanted out of an instrument and liked the idea of a modular system with a feeling of uniformity and consistency in how it looked, felt, and operated. Having played around with electronics since I was young, I decided it was time to jump in headfirst and design my own modular system that would embody all the ideas I had about what a DIY modular should be:

  • 4U / banana format with individual modules.
  • Use only modern, jellybean components wherever possible.
  • Avoid complicated calibration or trimming.
  • Use modern construction – stacked boards, PCB-mounted controls etc.
  • Compatibility with Eurorack signal levels / impedance etc.
  • Consistency between modules in both look & feel, and operation.
  • Good documentation that targets non-expert builders.
  • Should be able to completely build and calibrate a module in a day.

And finally, the dot point with which I’ve tried to guide my module design process:

  • Don’t be clever, don’t be dumb.

Which just reminds me that a module should have a clear identity and direction behind it that is clearly communicated to the user, avoiding feature creep and making sure that the front panel dictates the circuitry and not the other way around (Don’t be clever), as well as not avoiding adding features that I know will be useful to the musician out of laziness or being too obsessive about the layout or aesthetics (Don’t be dumb).

So that’s the story behind, Slightly Nasty. Maybe it will resonate with you, and you’ll think about adding some Nastiness to your own studio!

Raynor Pettge


Q: What’s this “Loudest Warning” stuff about, anyway?

A: The Loudest Warning format is just a set of guidelines dictating the size and mounting hole layout for 4U synth module front panels, created by Charlie Kerr. You can think of it as being a bit like “Eurorack for 4U”. It basically means that now developers wanting to design 4U modules have a standardised physical layout to work from, to ensure that different designer’s modules can be mixed and matched in a system.

Q: Is module (X) a clone of module (Y)?

A: No! All Slightly Nasty modules are new, ground-up, from-scratch designs. I don’t have anything against cloning vintage circuits, but I just have zero interest in doing it myself – that takes all the fun out of the design process!

The concept or functionality of some modules may be inspired by past synths, but it’s often more a case of convergent evolution – some things in analogue electronics just suggest themselves based on the fundamental building blocks available.

Q: I see a lot of modules listed as “in development” on the module page. Does this mean they’re just front panel ideas you’ve drawn up?

A: No! Any module that has been listed on the module page already exists as a functioning prototype in my rack. “In development” means that either there’s more work to do to refine the functionality, or the final PCBs / documentation etc. haven’t been completed yet.

There are actually plenty of other modules that do just exist as front panel designs at this point, but I won’t add a module to the page until it’s a serious prospect.

Q: Why aren’t you selling these in DIY retail outlets?

A: I do! Slightly Nasty PCB and (white) panel sets are available at Modular Addict.

Q: Are you an electrical engineer? Where did you study?

A: “I guess?” and “My shed” respectively. I’m actually a film editor, animator, and motion graphics artist by trade.