Stefan Tretau – St Modular

1. Favourite knob or fader or switch on a piece of gear and why?

Lots of Freq Knobs

First of all, I love every cutoff control. It is just such a powerful and enjoyable part of subtractive synthesis, that it will always be my first and preferred choice when looking for a knob to turn.

Elektron Octatrack

Second, the Elektron Octatrack fader is definitely one of the most powerful controls for a wide range of parameters, be it effects or sample processing. The possibilities are endless and its so easy to use.

Contour – Shuttle Express

Last, but not least, I bought a multimedia editor controller called “Contour – Shuttle Express” that allows me to create shortcuts for certain functions in the Eagle CAD program, which I use to design circuit boards. This has drastically improved my efficiency and speed when designing PCBs.

2. Do you have an ‘almost’ perfect bit of kit? What would you change?

S-CAT Double-Trouble Dual Filtered Distortion

I recently bought the S-CAT Double-Trouble Dual Filtered Distortion and I would immediately call it a perfect device. It has two channels, one optimized for synths and one for drums, and sounds delicious. I started to used it with the Roland TR8-S and the Behringer TD-3-MO and immediately went into an acid-frenzy. Here’s a video snippet where I also used it with the little Roland T-8 Aira compact groovebox.

Fun thing! :-

Blokas Midihub

Also worth mentioning is the Blokas Midihub, an interface and standalone MIDI processor that is as flexible as a midi interface can get. With the included editor, you can configure every midi setting imaginable. The only improvement would be a larger version with at least 8 channels.
Finally, the “GIVE2“ Oscillator I designed is still my favorite and I use it in almost every single patch. The only thing I would change in a future version would be to add faders instead of knobs and VCAs for each waveform at the mix output.

GIVE2 oscillator

3. What setup do you bring on holiday or tour or commute etc.?

A couple of years ago I put together a small Eurorack case that would somehow eliminate my GAS for the Buchla Music Easel (I named it “Euro Easel” ;-} ). It’s a small case with quite some limitations, but it has just the right modules to create very interesting sounds…. and it worked, I haven’t bought the Easel yet 🙂 It’s my travel case that I choose to take on vacation. You can find some videos about it here.

Takin’ it Easel

If I can’t take the travel case with me, I like to use an iPad or the three Aira Compact Grooveboxes, which are definitely fun.

4. What software do you wish was hardware and vice versa?

There are many multi fx vsts available, but there are just few ways to add multi fx with a hardware device that is not a pedal. I currently use the Octatrack to add effects to the main output. But I would like to have a device that looks like one of the Pioneer FX series units and has a functionality like Sugar Bytes Turnado VST, Fabfilter Effects VST or the Ozone Mastering Tools – and nothing less 😉

VCV Rack

If VCV Rack didn’t already exist, I would want to see some sort of modular software to test and review modules. Fortunately, VCV Rack is already the perfect solution for that. It has helped me to come up with new module designs that combine various module functions into one unit. In VCV Rack I tested their practical application in advance before writing schematics and making prototypes.

I can’t think of any other hardware that I would like to see as a software solution.

5. Is there anything you regret selling… or regret buying?

I wish I still had my Korg Electribe R and the Clavia Nord Micro Modular. They were way ahead of their time and I really enjoyed using them.

These were some of the last sounds I made with the Micro Modular, and it breaks my heart not to have it on my desk today.
There are some modules I bought that I didn’t keep for long. But the list would be too long to mention them here.

As for my designs, there are a few modules I have published that I regret creating.
Mostly because my design skills have improved and I wouldn’t design them the way they used to be published. But I won’t tell you which ones they are 🙂

6. What gear has inspired you to produce the most music?

The ST Modular Beast

Definitely my modular. Especially the last album „Ostinato Modulare“, released in 2020, is strongly inspired by modular synthesis. But also other releases have their origin in melodies and sequences I created on my modular system.

A little close on the ST Modular Beast

Also worth mentioning is the “Mopho“ from Dave Smith Instruments, which I used very often in the past. It’s such a great sounding and powerful little instrument when used with a software editor.

Little Mopho hiding there

I also often used the Korg Gadget iOS app to sketch out ideas that eventually found their way into a final track.

7. If you had to start over, what would you get first?

Any Groovebox (Syntakt, Roland TR8-S, or Roland MC707 or similar)

Elektron Syntakt

8. What’s the most annoying piece of gear you have, that you just can’t live without?

My soldering iron! I used to love soldering and enjoyed that deep yoga-like relaxation of soldering in repetition and deep concentration. But the solder fumes and flux residue, the time it takes me to solder prototypes and troubleshoot, and the fact that my body doesn’t like sitting in one position for long periods of time are increasingly annoying me.

Soldering iron

9. Most surprising tip or trick or technique that you’ve discovered about a bit of kit?


I would like to mention the moment when I found out how easy it is to order ready soldered PCBs. I used to solder all SMD components myself and at some point decided to use PCB assembly for prototyping. This dramatically increased the speed at which I could work on my PCB designs. That was both a surprise and a relief.

Closer to the PCB

Apart from that, almost every single unit has some “hidden” features that surprise me – like the ducking functionality with the FX tracks on the Syntakt, the control-all functionality on most Elektron units, or the way you arrange effects in scenes on the Octatrack.

Also, a modular system is an endless source of “happy little accidents,” as Bob Ross would say. There are so many different techniques to use CV. Every time I patch, I’m surprised how musical challenges can be solved with modular control voltages. I remember being overwhelmed by the possibilities offered by a single function generator. Depending on the patching technique you can use it as an oscillator, a filter, a distortion and an envelope with sustain stage.

Not what you think of when you see a module like this, is it?

A single module can be a world in itself, spreading its CV tentacles into an endless modular universe full of surprises.

Artist or Band name?

Stefan Tretau / ST Modular / ST Records


From Ambient to Techno


Stefan Tretau

Where are you from?

Oberhausen, Germany

How did you get into music?

Well, it’s not the piano and guitar lessons I used to get, but it was actually a friend’s Roland MC- 303 that I was lucky enough to use in 1999. That was my rabbit hole that I never got out of.
Shortly after that we bought a Roland MC-307, a Future Retro 777, a TB-303, a Micro Modular and a Jomox Xbase 09 and we started playing acid live acts as Complexx303“ in the early 2000s. Some time later it was just a small step to jump into the Eurorack universe. I bought my first Eurorack modules in 2016.

Stefan’s first eurorack case

ST Modular also started with a little push from a friend. He showed me how to build a Schmitt- Trigger oscillator, and I couldn’t believe how easy it was to recreate it on a breadboard. That was the second rabbit hole that somehow replaced the synthesizer-hole for some time. So instead of making music, I breadboarded, read books, created magic smoke, and eventually designed a desktop synthesizer, effects pedals, and a first Eurorack module, a passive mult.

Live synth setup

However, before I got into Eurorack designs, I focused on pedal and synthesizer designs. In the video linked here, you can see how I create all sorts of noises with these DIY boxes. You can also see a first logo design there, which is the predecessor of the current ST Modular logo.

Now that I had a foot in the door I could not resist to deal further with concepts and circuit diagrams and spent whole weekends researching on the internet and watching youtube tutorials.

First synth design called Dillen in 2015

When the first working Eurorack module was built (Triple Tom), I didn’t actually intend to offer modules or boards to other builders. It was then the builders themselves who kept asking for boards and finally got me to make a first attempt to offer PCBs in cooperation with in 2018.
And ST Modular was born.

What still drives you to make music?

That moment you surprise yourself.

How do you most often start a new track?

A kick and a bassline or a sound/melody that fascinates me.

How do you know when a track is finished?

I used to be very fast at producing and it wasn’t uncommon to finish a track in one day. I once participated in a remix contest for a label called “Karmarouge” and produced and submitted my remix within a single day. Surprisingly, my track was chosen to appear on the final vinyl release.

So, I’m not a perfectionist I guess and I don’t spend hours working on a snare sound.
If the track conveys a certain vibe, I can’t remove anything superfluous from the mix and nothing else extremely bothers me, it’s done!

ST modular System

As for the ST modular designs, each new prototype has to go through several weeks of extensive testing in my case. I design modules primarily for my personal use. If I don’t like the experience of playing with it, it doesn’t get released. I have a whole case full of finished prototypes that I have never published. They work technically fine, but they somehow didn’t turn out the way I had imagined.

Show us your current studio

Attic home studio
To the left of the Attic home studio
Center of the home stuio
Left side with the modular beast

Best creative advice that you’ve ever heard?

Just sit down and start!

Promote your latest thing… Go ahead, throw us a link.

ST Records – Latest Release „Ostinato Modulare“

ST Modular – Euphoria (DIY Semi-Modular Synthesizer)

ST Modular – Eurorack DIY

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