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How are 3.5mm MIDI jacks wired?
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There are two incompatible standards for 3.5mm (1/8”) TRS MIDI, commonly called Type A and Type B. They swapped the current source and sink pins, so a Type A cable won’t work with a Type B jack and vice versa.
TRS Pinout
| Tip / Ring | Type A (AKAI / Arturia) | Type B (Korg / Make Noise / Novation) |
|---|---|---|
| Tip | Data (current source) | Data (current sink) |
| Ring | Data (current sink) | Data (current source) |
| Sleeve | Ground | Ground |
What Do “Source” and “Sink” Mean?
In MIDI, data is sent as a current loop — not as a voltage level like audio or UART.
- Source = the pin that sources (pushes out) the current. It connects to the transmitting device’s optocoupler / LED driver.
- Sink = the pin that sinks (receives) the current back. It connects to the receiving device’s optocoupler / current loop return.
Because MIDI is a unidirectional current loop, swapping source and sink breaks the circuit entirely — no current flows, so no data passes. This is why Type A and Type B cables are incompatible even though both use the same 3.5mm TRS plug.
You don’t need to think about source/sink when wiring a Type A jack — just follow the standard wiring (Tip → TX, Ring → 3.3V via 220Ω). The terms mainly explain why the two standards are physically incompatible.
Which One Should I Use?
- Edrumulus / most DIY drum modules: typically use Type A (Arturia / AKAI wiring)
- Novation / Focusrite / Korg gear: typically uses Type B
- Cables are NOT interchangeable — using the wrong type causes silent failures (no data passes)
Roland / BOSS (Type A Confirmed)
Roland and BOSS explicitly use Type A for their 3.5mm TRS MIDI jacks. Their support documentation states: “Most all Roland and BOSS devices use MIDI TYPE A and AMEI MIDI standard.”
| Device / Cable | Type | Purpose |
|---|---|---|
| Roland P-6 (AIRA Compact) | Type A | 3.5mm MIDI IN/OUT jacks |
| BMIDI-5-35 | Type A | 3.5mm TRS → 5-pin DIN MIDI cable |
| BCC-1-3535 | Type A | 3.5mm TRS → 3.5mm TRS MIDI cable |
DIN-to-TRS mapping for Roland/BOSS Type A:
- MIDI DIN Pin 4 (Source) → Ring
- MIDI DIN Pin 5 (Sink) → Tip
- MIDI DIN Pin 2 (Shield) → Sleeve
Always check your device’s manual or schematic for the 3.5mm MIDI pinout. If in doubt, use a multimeter in continuity mode to buzz out the ring/tip connections to the optocoupler or UART pins on the PCB.
Practical Tip for Edrumulus Foot Triggers
If you’re adding a 3.5mm MIDI output to your ESP32-based foot trigger circuit:
- Use a 3.5mm TRS jack (or 3.5mm stereo jack)
- Wire as Type A unless your target gear specifically needs Type B:
- Tip → 220Ω resistor → TX pin (through UART / optocoupler)
- Ring → 220Ω resistor → 3.3V (current source for Type A)
- Sleeve → GND
- Test with a known Type A cable (Arturia, AKAI, newer Novation cables are colour-coded)
If you only need MIDI-over-USB (Edrumulus default), you don’t need the 3.5mm MIDI jack at all — the ESP32 presents as a USB MIDI device. The 3.5mm jack is only useful if you want to connect to hardware drum modules, synths, or sequencers that lack USB.In the case of the Roland P-6, its USB-C port is typically used for power and audio/MIDI to a PC, so using MIDI-over-USB with an ESP32 isn’t practical. The 3.5mm TRS MIDI jack is the right choice for connecting to the P-6.
#midi #wiring #edrum #midi-jack #trs