Ilse is an elegantly minimal, yet fully functional synthesizer voice in a compact 10 HP Eurorack module. The only thing you need to let it meow is a CV source to trigger its 1V/Oct frequency input (or a MIDI to CV converter and a MIDI sequencer) . Because it has a low part count it is ideal for Eurorack beginners or entry-level DIY projects.
Ilse is named after a cat, living in the legendary “Villa” in Weimar, Germany. The “Villa” was a place where a community lived and came together. Many underground concerts and parties took place here before the house got sold, renovated, and the mayor moved in. We created the graphics on the aluminum face-plate in her memory. Ilse (the synth) makes great acid sounds, so it was only logical to illustrate a cat tripping. Turn the knobs to make her look around or roll her eyes.
Ilse is designed to be affordable, easy to build, yet flexible, and feature rich. It is a synthesizer voice for your Eurorack, but can even be driven without a rack using two 9V batteries (not included).
Ilse is fully open source (KiCad schematic and layout is available in a git repository) and inspired by Syntherjack’s single-chip synthesizer Totoro. Check out his website with nice explanations, e.g. on the filter (we use the same filter on Ilse). We extended the design for external voltage control on filter, oscillators and LFO. Unlike Totoro, Ilse is designed around a unique oscillator design, which integrates the exponential conversion directly into the oscillator core. This results in an efficient circuitry saving you build time, parts and costs.
PCB and face-plate are manufactured in the EU. Kitting was done by our friends from Befaco in Barcelona. Complete assembly manual can be found in our forum.
Technical specifications
Functions
- Two saw tooth oscillators
- Bridged-T low pass filter with resonance control
- Triangle LFO with speed control, and routing to filter and/or oscillators
- Simple mixer and detune for oscillators
Controls
- LFO Speed, Filter Modulation, Osc Modulation
- Filter Cutoff, Filter Resonance
- Tuning, Osc2 Detune
- Osc1/Osc2 (Filter in)
- Output volume
Input/Output
- 1V/Oct CV for oscillators (0-5V)
- Gate (0-5V)
- Filter cutoff (0-5V)
- External filter input
- Volume controlled output
- LFO Speed (linear, via solder pad on back, 0-8V)
- Oscillator 2 detune (linear, via solder pad on back, 0-8V)
Current draw per Eurorack rail
- +12 V: 22mA
- -12 V: 18mA
- +5 V: NC
Dimensions
50mm wide (10HP), 128.5mm high (3U), depth in rack: 23mm, overall thickness: 43mm
Deep dive
You might as well just examine the schematics in the simulator and build your own synthesizer from it. It uses a neat trick to build the exponential converters directly into the saw tooth oscillators as you can see from the simulation below. Note that the tuning of the oscillators is not temperature compensated and will thus change with room temperature. We would not recommend using Ilse in a stage situation where reliable and exact pitches are important.
It features a simple voltage controllable low pass filter that you can modulate with the inbuilt LFO or an external source.
Ilse was designed for educational use and was used in an introduction to electronics course. For more details on the schematics see the course material.