Continuing my analog synth module series, I decided to design a Simple LFO (Low-Frequency Oscillator) for modulation duties in my Eurorack setup.
The goal was to make something compact, stable, and musical — a small utility module that delivers smooth, predictable modulation for filters, VCAs, and pitch control.
Concept
An LFO is one of the most essential modules in a synthesizer — it provides cyclic voltage changes that bring patches to life.
I wanted mine to be minimal but flexible, with multiple waveform outputs and a wide frequency range for both slow evolving movements and faster modulation effects.
Circuit Design
The design is based on a triangle core oscillator, similar to many classic analog LFO circuits.
The core uses an op-amp integrator and a comparator to generate a stable triangle wave, which is then shaped into additional waveforms.
The circuit provides:
- Triangle Output
- Square Output
- Sine Output (wave-shaped)
A simple rate potentiometer controls the oscillation frequency, and a range switch toggles between slow and fast modes for extended usability.
PCB & Layout
I designed the PCB to fit in 4HP Eurorack format, powered by the standard ±12V supply via a 10-pin header.
All jacks and controls are mounted directly to the PCB for sturdy, reliable assembly without extra wiring. The compact design keeps noise low and output signals clean.
Panel Design
The front panel follows my usual style — laser-engraved aluminum, labeled clearly with waveform outputs and rate controls.
The layout is simple and intuitive, so you can patch it instantly and get movement into your sounds right away.
Performance
The LFO runs smooth and stable, with perfectly symmetrical triangle and square waves.
At low rates, it creates slow, evolving modulations; at higher rates, it can even reach into audio-range frequencies for FM-style effects. The sine output adds softer modulation for subtle filter sweeps or vibrato.
Final Thoughts
This Simple LFO turned out to be one of my favorite utility modules — reliable, compact, and perfect for shaping motion in any patch.
It’s a small project but an essential one, especially for anyone building their own analog voice chain.