Emulation of the Roland TR-909 Rhythm Composer (1984), a drum machine with analog voices, sampled hi-hats and cymbals, and a step sequencer.
It runs the original sequencer firmware on an emulated CPU, and models the voicing board part by part from the service notes.
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
With the version 1.0 program ROM, a new ro-drums-909 holds the factory patterns. Here it plays them as a new instance starts, every knob at its default, in mono, with no effects: each pattern four times at the default tempo, 120.6 BPM, and the song, track 1, at its stored tempo, 110.3 BPM (TEMPO with TRACK 1).
A real TR-909 playing the song, on YouTubeMeasured against AudioRealism's recordings of a late TR-909 on a fine grid of knob settings, the unit it is calibrated to. Method: How it was made.
The voicing board and the switch board, every part where the service notes draw it, with the clap's trimmer TM, the circuit by serial number (Board revisions), and a scope on any pin of any part. SERVICE in the guide
Roland changed the TR-909 during production. The service notes list each change by the first serial number to have it (SN p.7). SERVICE’s circuit setting picks the unit by serial number, from the first units (360100) to the late board (426700 up, the default), and the model puts back the parts each later change replaced. Every other part is the calibrated unit’s, a late board. The setting is saved with the session. SERVICE in the guide
| From serial | Parts | Change | What it does | Modelled |
|---|---|---|---|---|
| 371500 | R495 (bass drum) | 150 kΩ from Q6’s base to ground removed | Surface-mounted on earlier boards (SN p.11) | Yes |
| 381500 | C9 (bass drum) | 0.22 µF → 0.33 µF | “For expanding the TUNE range” | Yes |
| 381500 | C87, R306, R312 (tape) | C87 removed; R306 4.7 kΩ → 47 kΩ; R312 470 kΩ → 4.7 MΩ | Tape LOAD | No: the tape interface isn’t emulated |
| 392600 | R442, R440 (crash, ride) | 33 kΩ → 10 kΩ | The sample clocks’ TUNE range | Yes |
| 393000 | D701 (power supply) | RD6.8JB2 → RD5.6JB2 | The reset at a brown-out | No: the supply isn’t modelled |
| 415300 | R417 (rim shot) | 12 kΩ → 3.3 kΩ | “For giving the voice more realistic sound” | Yes |
| 415300 | C134 (hi-hat) | 10 µF → 0.01 µF | “For rolling off unnecessary lower frequencies” | Yes |
| 415300 | R392, R393, R495, C600 (TRIG OUT) | 22 kΩ and 10 kΩ → 1 MΩ; a jumper → R495 1 kΩ; C600 0.1 µF added | Keeps the rim shot’s TRIG OUT pulse out of TAPE SYNC | Yes |
| 415300 | C500–C512 (jack board) | 0.01 µF to ground at each jack added | “Noise is high in OUTPUT” | Yes |
| 426700 | C54, R194 (tom noise) | 0.0022 µF → 0.0047 µF; 47 kΩ → 100 kΩ | “To emphasize attack of TOM TOMs” | Yes |
The program ROM changed too: group A, with no version label (SN 360100–393899); Ver. 1, an EPROM or a mask ROM (SN 403900 on); Ver. 2, which fixes STOP/CONTINUE under MIDI clock. ro-drums-909 runs version 4.0 at every serial number. A version 1.0 ROM only makes the factory patterns, which 4.0 dropped (the guide).
The tape interface (SAVE, LOAD, VERIFY, TAPE SYNC's input), the cartridge, TRIGGER OUT as a plugin output, the clock, start, stop and song select on MIDI out, the analog voices' own power-on transients (they start at their operating points), and the supply rails' ramp.
Roland's v4.0 program runs unmodified on an emulated uPD7811, with the CPU board's battery RAM, key and LED matrices, MEAS/TEMPO display, TEMPO and TOTAL ACCENT pots, MIDI and DIN sync, driving the voicing board through its trigger latches and accent DACs. Every procedure in the owner's manual behaves as the manual says, the firmware's own quirks aside: 54 checks. Against a real unit's recordings, shuffle is within 0.84 ms at all seven settings and the 40 flam recordings within 0.7 ms.
Every circuit of the voicing board and the jack 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 and rim shot within 0.12 % RMS, the clap 0.65 %, the jack board 0.35 %, the hi-hat and crash 0.45 % and the ride 0.6 % at their 192 kHz; the VCOs' pitch within 0.01 %. The noise generator and the hi-hat's and cymbals' counters, ROMs and latches are their logic, edge by edge.
The schematic doesn't fix the pots' laws, the trimmer or the parts' spread. These were fitted to AudioRealism's recordings of a late TR-909 at every knob on a fine grid, each fit checked on settings held out of it, and on other units' recordings.
| Part | Schematic value | Fitted |
|---|---|---|
| Bass drum C8 | 0.33 µF | 0.40 µF |
| Bass drum R44 | 22 kΩ | 36 kΩ |
| Snare VR7 | 500 kΩ | 600 kΩ |
| Clap trimmer TM, wiper | 25.5 % | 30 % |
| Crash VR25 | 10 kΩ | 8.36 kΩ |
| Cymbal clocks' 4011UB gates, drive | typical | × 1.72 |
With the schematic's values, the bass drum's log-spectral distance from the unit is 11.7 dB and the toms' tuning is 46–80 ¢ off RMS; fitted, 4.2 dB and 14–20 ¢. The clap's TM in the service notes, 2 Vp-p at its MULTI OUT, leaves the clap 6 dB under the other voices: its spikes are narrower than the unit's.
Its renders measured against the same real unit, at the same knob settings.
| Source | Toms' tuning | Crash and ride clocks | Bass drum sweep, TUNE 75 % | Open hat at DECAY 0, to −20 dB |
|---|---|---|---|---|
| Real unit | — | — | 14.4 ms | 136–137 ms |
| ro-drums-909 | within ±28 ¢ | within ±21 ¢ | 14.5 ms | 136–137 ms |
| Roland's software | low 79–120 ¢ flat, high 150–210 ¢ sharp | 29–118 ¢ under | 20.9 ms | 31 ms |
Roland's software also places the clap's fourth burst 3–5 ms late, and its rim shot's tail is half as long. ro-drums-909 was calibrated on this unit; Roland's software wasn't.
Measured with Roland's TR-909 software 1.1.3: single-knob sweeps around its default kit, at 48 kHz, MIDI velocity 127.
The sequencer program and the hi-hat's, crash's and ride's samples are in ROMs, Roland's copyrighted work, so they aren't included. With the images from MAME's tr909 set, ro-drums-909 runs the program, tr909_v4.ic609, on an emulated CPU, and plays the samples from their ROMs. Without the program ROM, it runs in voice mode: the same voices over MIDI, with no sequencer. Without a sample ROM, that voice is silent. The version 1.0 program ROM gives a new instance the factory patterns. The ROMs and voice mode
Roland's logo and the model names are trademarks, so their places are blank: three on the top panel and one on the rear. Each place takes an SVG or PNG file of your own in artwork/tr909/ in the ROM folder: drawn yourself, or generated with an AI tool such as Claude or ChatGPT. Panel artwork