build reference · analog voltage-controlled circuits
A dozen minimalist, breadboard-first analog building blocks — each one musically useful on its own, all speaking the same CV & gate language so they snap into a modular rack or combine into standalone synths. Beginner-buildable, in the Moritz Klein / Erica Synths EDU tradition, specced at Eurorack standard with 9V-battery simplifications noted throughout.
Everything below is designed around one shared electrical language. Get these levels right and any module can drive any other — that is what lets the same circuits act as rack modules or fuse into a single instrument. Toggle between the full Eurorack-compatible spec and the simplified 9V-battery version from the build videos.
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All jacks are 3.5 mm mono, tip = signal, sleeve = shared ground. There is no separate return — patch cables are just voltage on a wire. Keep one common 0 V ground across every module.
The classic subtractive voice: a pitch source sets the note, an oscillator makes the raw tone, a filter carves its brightness, and an amplifier shapes its loudness over time — with envelopes and an LFO bending everything as it plays.
Swap the order, add a wavefolder before the filter, feed noise into a sample & hold to modulate pitch — the recipes at the bottom do exactly this.
Twelve circuits. Click any card to open its theory, core circuit, parts list, and breadboard steps — plus the Eurorack ↔ 9V differences and an upgrade path once the basic version sings.
The same circuits, wired permanently and boxed up, become finished instruments. Each recipe lists a signal chain and what to hard-wire vs. leave on a knob.
Build so you can hear progress early and debug one variable at a time. Power first, then a tone you can listen to, then everything that shapes it.
This reference is step one. The plan is to make the synth something you can actually play in the browser here in the Lab, then close the loop back to real hardware — the software toy and the workbench build, side by side.
This page — the full family of circuits, the shared CV/gate standard, and standalone-synth recipes. The spec everything else is built from.
An in-browser modular you can patch and hear: a Web Audio VCO → VCF → VCA driven by an ADSR and an LFO, with the same knobs and signal flow described here. Drag a cable, turn a cutoff, play a note — no soldering required. This is the version that becomes a true Lab instrument.
Once the voice is dialled in on screen, the reference doubles as the build sheet for the physical version — breadboard first, then maybe a small PCB or panel. The browser becomes the place you prototype a patch before you wire it.
Want to follow along or help shape it? The contact page is the way in.