108 GBA PSG Voice
Turns a Game Boy Advance into a synth voice for your modular. The Workshop Computer loads custom
software onto the GBA over its link cable using the GBA's built-in multiboot - no cartridge, no
modifications. Your CV, knobs and gates then play the GBA's four sound channels, and the GBA sends
its notes, gates and buttons back to the rack. Sound comes from the GBA's headphone jack; the
sound editor is on the GBA's own screen. Works with the Game Boy Advance, GBA SP (with the SP
headphone adapter) and Analogue Pocket.
THE CABLE. Wire one end of a link cable to the Workshop: GBA pin 5 (SC) to Pulse Out 1 through a
1k resistor, pin 3 (SI) to Pulse Out 2 through a 1k resistor, pin 2 (SO) to Pulse In 1, and pin 6
to ground. Leave pins 1 and 4 unconnected. Do not leave out the resistors - the pulse outputs swing
to about 6V and the GBA runs at 3.3V. A Game Boy Color cable is best, as it has all six wires.
GETTING STARTED. Take the cartridge out. Switch on the Workshop first, then the GBA. The LEDs light
in sequence as the software loads (about six seconds), the GBA screen goes green, and the MAIN page
appears. Push the Z switch down to hear a note. If nothing happens, power-cycle the GBA - always
needed after re-flashing the Workshop.
PLAYING. CV In 2 is 1V/oct pitch, the Main knob is channel 3's level, X and Y are attack and
release, and the Z switch triggers. CV Out 2 is the quantised pitch, CV Out 1 the gate, and Audio
Out 1 and 2 are the GBA's A and B buttons as gates. Everything else is yours to assign.
THE EDITOR. START opens it, SELECT + Left/Right changes page, A + D-pad changes values. Eleven
pages: MEM (16 patch slots), CHAN, TRIG, ENV, MIX, BTN, MAP (modulation matrix), ORN (arpeggios),
DRUM, CAL (trim 1V/oct tracking) and SET (key and scale quantising).
See the user manual PDF and README.md for a guided tour, and TECHNICAL.md for the full reference.
Panel
Level (Ch. 3)AttackReleaseMod 2Mod 3Mod 1PitchGBA SO (MISO)GateA button gateB button gateGate outQuantised pitchGBA SC (clock)GBA SI (MOSI)Controls
Level (Ch. 3)
Level of channel 3 by default; assignable on the MAP page
Attack
Attack, both envelopes together, by default; assignable on the MAP page
Release
Release, both envelopes together, by default; assignable on the MAP page
Modulation: An eighth source on the GBA's MAP page - assign it to anything. Up is full, middle and down are zero
Trigger: Momentary down fires a note; a column of the GBA's TRIG grid
Inputs & Outputs
Inputs
Outputs
Inputs
Mod 2
Unassigned by default; assignable on the MAP page with per-voice tickboxes, or armable as a trigger source on the TRIG page
Mod 3
Unassigned by default; assignable on the MAP page with per-voice tickboxes, or armable as a trigger source on the TRIG page
Mod 1
Unassigned by default - nothing should move that you did not patch. Give it a job on the MAP page, or arm it as a trigger source on the TRIG page
Pitch
1V/oct pitch CV. Trim tracking on the GBA CAL page (CV inputs are not factory calibrated)
GBA SO (MISO)
Serial data back from the GBA. Read directly via PIO, not the 48kHz pulse path
Gate
Gate and trigger. Off in the factory patch - tick PU2 on the GBA's TRIG page to use it. Edges shorter than the 1ms poll are still caught
Outputs
A button gate
High while the GBA's A button is held - the performance gesture as a patchable voltage
B button gate
High while the GBA's B button is held
Gate out
5V while a note is sounding
Quantised pitch
The note the GBA is sounding, as calibrated 1V/oct. Turns the pair into a quantiser for the rest of the rack
GBA SC (clock)
Master serial clock driven by the RP2040 (PIO), inversion handled in hardware
GBA SI (MOSI)
Serial data to the GBA (payload upload, then the live input stream)
LEDs
Link (solid booted, blinking connecting)
Gate in / upload progress / fault code bit 0
Note sounding / upload progress / fault code bit 1
Editing on the GBA / upload progress / fault code bit 2
Edit page bit 0 / upload progress
Edit page bit 1 / upload progress
README
GBA PSG Voice
A program card for the Music Thing Modular Workshop Computer that turns a Game Boy Advance into a synth voice for your modular.
The Workshop loads custom software onto the GBA through its link cable using the GBA's built-in multiboot, so you need no cartridge and no modifications. From then on, signals flow both ways: your CV, knobs and gates play the GBA's four sound channels, and the GBA sends its notes, gates and buttons back to the rack. Sound comes out of the GBA's headphone jack, and the sound editor is on the GBA's own screen.
User manual (PDF) · Technical guide · Program Card Firmware
Videos
 |
 |
 |
|---|---|---|
| Quick setup guide | Bleepy demo · walkthrough | Drone-y demo · walkthrough |
What you need
- A Game Boy Advance, GBA SP or Analogue Pocket, with no cartridge in it. The GBA SP has no headphone socket, so it needs Nintendo's SP headphone adapter.
- A link cable wired to the Workshop's pulse jacks, with two 1 kΩ resistors (see below).
- The firmware,
UF2/gba_link.uf2, flashed to the Workshop Computer.
Getting started
- Connect the GBA to the Workshop with the link cable. Leave the cartridge slot empty.
- Switch on the Workshop Computer first, then the GBA.
- The Workshop's LEDs light in sequence as the software loads (about six seconds).
- The GBA screen goes green, then shows the MAIN page.
- Push the Z switch down. You should hear a note.
Sound comes from the GBA's headphone jack. It is quiet by Eurorack standards, so plug it into a mixer or another input with gain.
Nothing happening? Power-cycle the GBA and try again. You always need to do this after re-flashing the Workshop. For fault codes and step-by-step checks, see the technical guide.
The cable
| Pin | Signal | Connect to |
|---|---|---|
| 1 | VDD | nothing |
| 2 | SO | Pulse In 1 |
| 3 | SI | Pulse Out 2, through a 1 kΩ resistor |
| 4 | SD | nothing |
| 5 | SC | Pulse Out 1, through a 1 kΩ resistor |
| 6 | GND | ground |
- Don't leave out the resistors. The pulse outputs swing to about 6 V and the GBA runs at 3.3 V.
- Use a Game Boy Color link cable if you can. They have all six wires; many third-party GBA cables don't.
- The two ends of a link cable may swap SO and SI. If nothing connects, the technical guide has a diagnostic that tells you which wire is which.
Connections
| Inputs | Default job |
|---|---|
| CV In 2 | 1V/oct pitch |
| CV In 1 | unassigned |
| Audio In 1 / 2 | unassigned |
| Pulse In 2 | gate / trigger (tick PU2 on the TRIG page) |
| Pulse In 1 | GBA SO (link cable) |
| Main knob | channel 3 level |
| X / Y knobs | attack / release |
| Z switch | down = trigger, up = assignable modulation |
| Outputs | Job |
|---|---|
| CV Out 1 | gate out |
| CV Out 2 | pitch out (quantised, 1V/oct) |
| Audio Out 1 | A button gate |
| Audio Out 2 | B button gate |
| Pulse Out 1 | GBA SC (link cable) |
| Pulse Out 2 | GBA SI (link cable) |
You can reassign every input, knob and the switch on the GBA's MAP page.
The GBA software
| Button | Does |
|---|---|
| START | open the editor / back to the MAIN page |
| SELECT + Left/Right | move between editor pages |
| D-pad | move around a page |
| A + D-pad | change a value |
MAIN
The performance screen. It shows the note playing, the level of each of the four sound channels (SQ1, SQ2, WAV, NSE) and the live inputs and knobs. Here the D-pad, A, B and shoulder buttons are for playing: trigger, hold, ornaments and more, all set on the BTN page.
MEM: patch memory
Sixteen patch slots, stored on the Workshop Computer. D-pad picks a slot, A + Up saves, A + Down loads.
⚠️ Saving overwrites the slot straight away. Check you are on the right slot first.
CHAN: channels
The core sound of each of the four channels: output (left / right / both / off), semitone offset, ornament, timbre (duty cycle or waveform), detune, noise pitch, and channel 1's pitch sweep.
TRIG: triggers
What fires each channel. Tick any combination of Pulse In 2, the Z switch, a GBA button, Audio In 1, Audio In 2 and CV In 1.
ENV: envelopes
Attack, decay, sustain and release for each channel, plus portamento and retrigger. The shape is drawn as you edit it.
MIX: mixer
Level (0–15) and left / right panning for each channel.
BTN: buttons
What each GBA button does on the MAIN page: trigger, hold, octave up/down, duty cycle, ornament slots, channel on/off and more.
MAP: modulation
The modulation matrix. Each source (CV 1, CV 2, Audio 1, Audio 2, the three knobs and the switch) gets a destination, an amount, and a tickbox per channel. An amount of +32 on PITCH is exactly 1V/oct.
ORN: ornaments
Six arpeggios or pitch sequences of up to sixteen steps. Set the length, rate and mode (loop, or play once), then draw the steps.
DRUM: drum mode
Turns incoming triggers into percussion on channels 3 and 4, leaving the two squares free for melody. Pick a sound for each input (kick, snare, hats, toms, clap and more) and set the threshold.
CAL: calibration
Trims how CV In 2 tracks 1V/oct (CV scale, offset and base note), and sets the master levels. The live tuner at the bottom shows the incoming note and the note being played, so you can trim until they match. You may need this page: every Workshop Computer's inputs are slightly different.
SET: settings
Master tuning, key, scale and octave. Choose a scale to quantise everything you play, and CV Out 2 becomes a quantiser for the rest of your rack. FREE turns quantising off. Four user scales can be edited note by note.
More
- Technical guide: building the cable in detail, fault codes, every page in depth, how the link works, and how to build from source.
- BENCH.md: step-by-step bring-up if it doesn't connect.
- diagnostics/: link and cable test programs.
By Andy Jenkinson (YT/IG @uglifruity), 2026. Built on Chris Johnson's ComputerCard library for Tom Whitwell's Music Thing Modular Workshop Computer. MIT licensed.