Powering MIDI Pedals Using Unused DIN Pins

Standard 5-pin DIN MIDI connections traditionally use only three of their five available conductors for transmitting serial data, leaving two pins entirely unused. To eliminate redundant wall warts and streamline pedalboard wiring, modern music equipment manufacturers repurposed these idle conductors to route low-voltage direct current (DC) power directly to MIDI foot controllers and pedals. This technique, commonly known as MIDI phantom power, allows a single cable to carry both control commands and operating power between rack gear, amplifiers, and floor units.

The Original 5-Pin DIN Configuration

The original 1983 MIDI 1.0 specification adopted the 180-degree 5-pin DIN connector (DIN 41524). Despite having five pins, the protocol was designed to operate as an opto-isolated current loop that required only three physical connections:

Because pins 1 and 3 were left electrically floating inside standard MIDI hardware, they offered an open pathway for custom hardware designs without disrupting the baseline communication protocol.

Implementing Phantom Power Over Pins 1 and 3

Pioneering guitar-rack and switching manufacturers, such as Rocktron, Digital Music Corp (later Voodoo Lab), and Axess Electronics, leveraged pins 1 and 3 to supply operating voltages to remote floor controllers.

In a standard 5-pin phantom-powered configuration:

  1. Power Injection: A DC power supply—typically 9V DC or 12V DC—is connected to a master unit (such as a rack effects processor, switcher, or specialized breakout box).
  2. Pin Assignment: The master unit's MIDI IN or OUT jack routes the positive voltage to pin 3 and the negative/ground return to pin 1 (or vice versa, depending on the manufacturer's internal schematic).
  3. Reception: Inside the compatible MIDI foot pedal, pins 1 and 3 are wired directly to the internal power regulation circuitry, bypassing the standard DC barrel jack.

Because standard MIDI outputs isolate pins 4 and 5 via optocouplers and leave pins 1 and 3 unconnected, sending low-voltage DC over pins 1 and 3 does not interfere with the transmitted MIDI data signal.

The Shift to 7-Pin DIN Connectors

While repurposing pins 1 and 3 on standard 5-pin cables worked, it created edge-case risks. Some MIDI cables only contained three physical conductors to save manufacturing costs, rendering phantom power non-functional. Additionally, if a user accidentally plugged a cable carrying voltage into equipment where pins 1 and 3 were tied to an internal chassis ground, it could cause electrical shorts.

To solve this, manufacturers such as Lexicon, Rocktron, and Mesa/Boogie adopted the 7-pin DIN connector:

A 7-pin female chassis jack accommodates a standard 5-pin MIDI cable without powering the unit, but when a 7-pin cable is used with a compatible controller, pins 6 and 7 deliver the necessary DC or AC current safely away from the standard MIDI data pins.

Requirements for Proper Operation

For low-voltage DC to function correctly over repurposed DIN pins, the setup must meet three hardware criteria: