303 Circuit Model

commonly modded Drag a knob to change the part. Click its value to reset it.

Hover or focus a part to see what it does.

TooltipsSay what a control does in the line at the bottom of the screen when you point at it. Messages show there either way.

De-clickEases the level over a few ms around each retrigger, where the real 303 clicks. Adds 3 ms of latency. Off is the original sound.

Fade 1.5 ms

Front-panel dials follow MIDI CC from any input, on any channel.

Your sound and pattern presets, the current sound and pattern, as one JSON file.

Source. Roland main board schematic, Feb 19 1982, with unclear values read from the TD-3 clone sheet. Parts on neither sheet are estimates. Running at 2× oversampling.

Pitch and VCO. A 6-bit R-2R ladder from 5.333 V gives 1/12 V per step. An exponential current charges C33 from 5.5 V to 12 V, then resets, smoothed with a polyBLEP.

VCF. Four coupled ladder stages with a tanh law per transistor pair, 18n bottom cap and 33n above, solved implicitly. Full feedback (k = 17) self-oscillates.

Envelopes and VCA. C62 decays through R138 + VR6 (200 ms to 2.5 s). Accent shorts VR6 and charges the sweep cap. The OTA VCA gets resonance compensation through C76/R100, and normal notes fade in through R_SOFT.

Mods. Dotted parts map mostly to Devil Fish controls: Normal and Accent decay, VEG decay, Soft attack, Slide time, Sweep speed and self-oscillating resonance.

Lexicon 224. Runs on its own 20 kHz clock with 12-bit gain-ranging converters, 16-bit words and a shared 32K-word delay memory. The core is Dattorro's published Griesinger-style plate network; the 224's own microcode is not public, so the hall, chamber, room and chorus variants are estimates.

Plate, Spring, Convolution. The other reverbs on the same slot: Dattorro's published plate as he gives it, a dispersive spring tank after Välimäki, Parker and Abel (stretched allpasses in a delay loop), and partitioned FFT convolution of real impulse responses (below) plus generated ones.

Convolution IRs. EMT 140 plate impulse responses by Greg Hopkins (CC BY). Room, silo, garage, Musikverein and On a Star impulse responses from Voxengo, free for any use. Trimmed to 3 s at 48 kHz; see irs/CREDITS.md.

RAT. LM308 stage with gain-bandwidth and slew limits from its 30p cap, 1N914 diodes to ground, then the 3.3n filter.

303 circuit model

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