This module is shared under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license. All credits go to Tom Wiltshire, founder of Electric Druid.
A Eurorack wavetable oscillator module built around the VCDO1 chip from Electric Druid. The VCDO1 is a digital wavetable + sub-oscillator chip in an 18-pin DIP, running its own DAC internally and exposing both main and sub waveform outputs.
- 16 main waveforms with smooth morphing via the Wave Select control
- 8 sub waveforms with 4 selectable octave offsets (+1 oct, unison, −1 oct, −2 oct)
- V/oct Note CV input (0–5V, 5 octaves) with V/oct gain trim and offset trim
- Exponential FM CV input (±5V) with zero trim
- Wave Select CV for main and sub waveforms (±5V each)
- Bitcrush amount with both panel control and CV input
- Glide (portamento) time with both panel control and CV input, plus a separate Glide on/off gate input
- Two simultaneous outputs: Main oscillator and Sub oscillator (10Vpp each, anti-aliased)
- Eurorack ±12V power via either 16-pin IDC or 3-pin JST connector
The module adds CV-controllable bitcrush and glide amounts on top of the original Electric Druid VCDO datasheet circuit.
| Jack | Range | Notes |
|---|---|---|
| Note CV | 0–5V | 1V/oct, scaled to chip's 0–5V range; trim pots adjust V/oct and offset |
| FM CV | ±5V (10Vpp) | Inverted, scaled, offset-shifted to 0–5V; zero trim |
| Main Wave Select CV | ±5V (10Vpp) | Inverted, scaled, offset-shifted to 0–5V |
| Sub Wave Select CV | ±5V (10Vpp) | Inverted, scaled, offset-shifted to 0–5V |
| Bitcrush CV | ±5V (10Vpp) | Mixed with front-panel Bitcrush Control via Amount attenuator |
| Glide Time CV | ±5V (10Vpp) | Mixed with front-panel Glide Time Control via Amount attenuator |
| Glide on/off CV | 0–5V (gate) | NPN-buffered, drives chip's digital glide input |
| Main Out | 10Vpp | 4-pole Bessel reconstruction filter (≈18 kHz), buffered, 1K series |
| Sub Out | 10Vpp | Identical filter chain |
┌───────────────────┐
Note CV ─► [V/oct + offset] ──► │ │
FM CV ─► [scale + zero] ─────► │ │ Main ─► [4-pole Bessel LP] ─► Main Out
MainSel ─► [scale + offset] ──► │ │
SubSel ─► [scale + offset] ───► │ VCDO1 chip │
Bitcrush ─► [pot + CV+amount] ─► │ (digital │
GlideTime ─► [pot + CV+amount] ─► │ wavetable │
Glide on/off ─► [NPN inverter] ─► │ oscillator) │ Sub ─► [4-pole Bessel LP] ─► Sub Out
│ │
Pots (Course, Fine, │ │
MainSel, SubSel) ────────────► │ │
└───────────────────┘
Eurorack ±12V ─► U6 (78M05) / U7 (79M05) ─► ±5V rails
- Eurorack ±12V in via J3 (3-pin JST) or J4 (16-pin IDC) — populate one
- Local U6 (78M05) generates +5V from +12V
- Local U7 (79M05) generates −5V from −12V
- R45 / R46 (10K) are optional minimum-load resistors
Note on the Electric Druid datasheet: The original VCDO1 datasheet circuit has an error in the negative 5V regulator wiring. This schematic corrects it — verify when copying from the datasheet directly.
The board has three trim pots that need adjustment for accurate tracking. You'll need: a multimeter, a calibrated reference tone source (a tuner app, another tuned VCO, or a 1V/oct keyboard).
RV1 — V/oct Adjust sets the per-octave gain of the Note CV. RV2 — Offset trim sets the DC offset of the Note CV (the "zero" pitch when 0V is applied). RV3 — FM Zero trim ensures no DC drift on the FM input when nothing is patched.
Procedure:
- Warm up. Power the module for at least 5 minutes — the temperature affects the chip and trim accuracy.
- Set baseline. Freq Course and Fine at 12 o'clock. Nothing patched.
- Tune the base pitch. Apply 0V to the Note CV jack (or short the jack tip to GND). Adjust RV2 (Offset trim) until the main output matches a known low reference (e.g., C2 = 65.41 Hz).
- Tune the per-octave gain. Apply +4V to the Note CV jack. Adjust RV1 (V/oct) until the main output is exactly 4 octaves higher than step 3 (e.g., C6 = 1046.5 Hz).
- Iterate. Step 3–4 interact slightly; bounce between them until both are accurate.
- Zero the FM input. With Note CV at 0V and nothing patched into FM, adjust RV3 (FM Zero trim) until probing AIN_Freq_Mod_CV (or the FM jack tip) shows ~0V DC.
If tracking drifts at the extremes (very low or very high notes), check the timing capacitor area on the VCDO1 (this is a chip-internal characteristic).
Local archived copies live in references/ so this repo stays useful if the upstream links die.
- VCDO1 datasheet (Tom Wiltshire / Electric Druid, 2015) — local copy · upstream — chip pinout, example circuit, and waveform reference. Note the negative-5V-regulator wiring error called out above; this schematic corrects it.
- Electric Druid VCDO1 product page
What's ready for builders today, and what's still on the TODO list:
Production assets (what you need to actually fabricate and assemble a final unit)
- Schematic — Rev 0.1.5 (PDF)
- PCB layout — in progress — multiboard layout in
kicad/, not yet separated for fab - Gerber files for fabrication — none yet
- BOM — BOMs - VCDO1 - Schematic Rev 0.1.2.pdf
- Final front panel (SVG/PDF for fab) — none yet
- License — LICENSE
Prototype assets (for breadboard / perfboard / 3D-printed-panel builds before final PCB)
- 3D-printed prototype panel STL — VCDO.stl
Documentation
- Photos of the assembled module — see photos/
- Demo video — none yet
- Build / assembly instructions — none yet
Want to help fill a gap (build photos, gerbers, an assembly guide)? Open an issue or PR.