Roland TR-808 Rhythm Composer emulation
Expect bugs, and changes before 1.0. The installers aren't signed yet, so macOS and Windows warn before opening them. How to open them
Nothing else is sent. Mailing list
Measured against Michael Fischer's recordings of a real TR-808 at every knob mark, the unit it is calibrated to. Method: How it was made.
The clips at the top: the rhythms printed in the TR-808's rhythm chart, as a new instance holds them, every knob at its default, in mono, with no effects; four bars at 120 BPM, BASIC-VARIATION at AB.
The main board, the voicing board and the switch board, every part where the service notes draw it, with the six trimmers and their procedures, the circuit by serial number (Board revisions), and a scope on any pin of any part. SERVICE in the guide
Roland changed the TR-808 during production. The service notes list each change by the first serial number to have it (SN p.15). SERVICE's circuit setting picks the unit by serial number, and the model puts back the parts each later change replaced. Every other part is the calibrated unit's. The snare and clap's "PORTION CHANGED" gives no serial, so it is a setting of its own, EARLY or LATE. Both are saved with the session. SERVICE in the guide
| From serial | Parts | Change | What it does | Modelled |
|---|---|---|---|---|
| 300 | C11, C203, R49 (INT clock) | .068 → .047 + .039; R49 150 kΩ → 100 kΩ | Keeps the clock in range against HD14584 hysteresis | Yes |
| 300 | C6, R44, R45 (cowbell) | .01 → .022; 390 kΩ → 150 kΩ; 330 kΩ → 100 kΩ | Lets the cowbell's frequencies be set in range | Yes |
| 10600 | R346, R332 (clap) | 1 kΩ → 680 Ω; 22 kΩ → 27 kΩ | “CP sound overmatches the rest in level” | Yes |
| 10600 | R127, R129, R131, C200, C202 (noise) | The DC path → C200 10 µF; R131 300 kΩ → 100 kΩ; C202 22 pF added | Keeps IC24's bias current off its output | Yes |
| 10600 | R106, R154, R182, R213, R242, R268, R298 (voice gates) | 22 kΩ → 10 kΩ | Gate drive at a lower COMMON TRIG | Yes |
| 10600 | R101, C201 (common trig) | 10 kΩ → 100 kΩ; 22 pF added | Stops the clap's high frequencies upsetting the other voices | No: the common trig is an ideal 1 ms pulse |
| 10600 | R91 (CPU), R25 (DIN sync) | 15 kΩ → 1 MΩ; 220 kΩ → 1.5 MΩ | The battery's drain; false triggering | No: outside what the model runs |
TRIGGER OUT, the footswitch jacks, SYNC OUT, the factory rhythm tracks 1 and 2 (no document lists their bars), hum, temperature drift, and the supply rails' sag.
Roland's program runs unmodified on an emulated uPD650C. Its I/O map and RAM format were worked out against the owner's manual, procedure by procedure. In time with a host, all 16 steps land within 12 ms of the grid, 5 ms late as DIN sync makes it.
Every circuit of the voicing board was transcribed part by part from the service notes into a netlist, which a circuit solver runs sample by sample: no voice is a hand-made approximation. Each netlist is checked against ngspice on the same circuit: the bass drum, snare, toms, congas, cowbell, clap, rim shot and mixer within 0.3 % RMS, the maracas 0.6 %, the cymbal 1.4 %, the hats 4 %, the claves 5–6 % from discretisation.
The schematic doesn't fix the pots' laws, the trimmers or the parts' spread. These were fitted to Michael Fischer's recordings of a TR-808, serial 103852, at every knob mark, and checked on the marks held out of the fit and on three other units' recordings.
| Part | Schematic value | Fitted |
|---|---|---|
| Cowbell's two oscillators, TM1 and TM2 | 540, 800 Hz | 558.3, 823.6 Hz |
| The metal squares' duty | 0.47 | 0.545 |
| White noise, TM4 | 130 mV rms | 190 mV |
| Clap offset, TM3 | mid | 0.37 |
| Bass drum VR6 | 500 kΩ | 585 kΩ |
| Cymbal R125 | 2.2 kΩ | 3.55 kΩ |
| Rim shot R318 | 220 kΩ | 165 kΩ |
Its renders measured against the same real unit, at the same knob marks. ro-drums-808 is the closer of the two on 95 of the 99 recordings both can play, on the marks it wasn't fitted to as well. Roland's accents swell its hits 3–6 dB more than the real unit's.
| Voice | Pitch, Roland's | Pitch, ro-drums-808 | LSD, Roland's | LSD, ro-drums-808 |
|---|---|---|---|---|
| Bass drum | −102 ¢ | −11 ¢ | 6.93 dB | 0.77 dB |
| Snare | −38 ¢ | +10 ¢ | 5.32 dB | 1.52 dB |
| Low tom | +67 ¢ | −7 ¢ | 5.75 dB | 2.99 dB |
| High tom | −44 ¢ | 0 ¢ | 5.36 dB | 3.06 dB |
| Cowbell | −23 ¢ | −4 ¢ | 3.28 dB | 2.53 dB |
| Cymbal | — | — | 2.89 dB | 1.57 dB |
ro-drums-808 was calibrated on this unit; Roland's software wasn't.
The sequencer program is in the CPU's mask ROM, Roland's copyrighted work, so it isn't included. With the image from MAME's tr808 set, d650c-085.ic4, ro-drums-808 runs it on an emulated CPU. Without it, it runs in voice mode: the same voices over MIDI, with no sequencer. The ROM and voice mode
Roland's logo and the model names are trademarks, so their four places on the panel are blank. Each place takes an SVG or PNG file of your own, named ro-drums-808-maker and so on, in the ROM folder: drawn yourself, or generated with an AI tool such as Claude or ChatGPT. Panel artwork