Microdesignum MIDI Control for EHX x9

The Microdesignum MIDI Control for EHX x9 is a retrofit MIDI module built into an Electro-Harmonix x9 pedal to give it full MIDI control. It targets the EHX B9, C9, Key9, Synth9 and Mel9, and Microdesignum also lists it for the Bass9¹². Once installed, it controls everything the pedal offers: the nine EHX programs, the four control buttons and the On/Off footswitch, plus every knob, with all parameters controllable via MIDI in real time¹³⁴.

The principle is that the module electronically simulates turning and pressing the pedal's control knobs and buttons, so the pedal responds to Program Change and Control Change MIDI messages as if you were operating it by hand¹. Each preset stores the EHX program number, values for all the effect potentiometers and a default state for the bypass footswitch³.

What it controls

The module gives full control of the x9 pedals' functions: the ON footswitch, the program selector (1 to 9) and the control knobs, which on the C9 are Dry, Organ, Mod and Click². The install service page lists the controllable parameters as Preset, Engage/Bypass, DRY, EFFECT, CTRL1 and CTRL2, or MOD, CLICK, or ATTACK, SUSTAIN, depending on the pedal variant⁴.

The module adds its own small control surface with a display, buttons and indicators³:

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When the pedal is powered on, user preset 1 is active by default³. Unsaved changes to the current preset are not permanently stored until you save the whole preset by holding the Save button; disconnecting power reverts them³.

Presets: 128 user and 9 factory

There are 128 user presets plus 9 factory, read-only presets³. Only the user presets, 1 to 128, can be activated by Program Change³. The factory presets PG1 to PG9 correspond to the original EHX programs 1 to 9, and when a factory preset is active the actual physical knob values are used; they can be selected only with the up and down buttons, held until the PG prefix appears on the display³.

Each user preset contains PGM, the EHX program 1 to 9, and PA1 to PA4, the stored knob values, with the number of knobs depending on the EHX pedal variant³. By default the EHX programs are cyclically predefined across Program Change numbers 1 to 128: PC 1 to 9 map to EHX programs 1 to 9, PC 10 to 18 map to programs 1 to 9 again, and so on through PC 127 mapped to program 9³.

One terminology note from the manual: the term "preset" in the module's manual does not correspond to the term "preset" in the original EHX pedal manual, where that concept is called "EHX program" or "factory preset"³.

MIDI settings: channel, Program Change and CC numbers

The module listens on one MIDI channel, numbered 1 to 16, with channel 1 as the default (displayed as C1)³. The MIDI OUT port resends every message that arrives at the MIDI IN port, so the pedal can sit in a MIDI chain³.

³

To reach the global settings menu, turn the pedal off, hold down the Edit button and turn it on; the display shows GLB. Use the up and down buttons to change values, then press and hold the Edit button until the display shows SAV to save and exit to preset mode³.

Knob behavior: virtual values and Realtime sync

During normal operation the physical knob positions are not applied; virtual values loaded from the preset memory are used instead³. In the Edit menu, with parameter PA1 or higher selected, the On button toggles a lock for the current knob³. Each knob's parameter value can run in Normal mode (0 to 127) or "Realtime sync" mode (shown as dashes), in which the real actual knob value is used any time the preset is active³.

Installation and versions

The module is sold in a Compact version and a Rack version, both as a module you install yourself; the EHX pedal is not part of the product¹⁵. The Compact module was listed as temporarily unavailable as of 26 October 2026¹. Microdesignum has tested the module on revision C (2014), D and E (2018) of the x9 boards, and notes there are more variants of the boards²⁶.

For full control, 16 wires and one component must be soldered¹². The installation takes about 1 hour by Microdesignum's estimate¹², though the installation guide states about 2 hours⁷. The steps, as Microdesignum describes them:

1. Open the pedal and remove the connectors, footswitch, buttons, potentiometers and program selector; attach the controller with its double-sided adhesive tape, which Microdesignum warns is very strong⁷.
2. Solder the power supply wires at the two soldering points, +9V and GND¹⁶.
3. Cut the wipers of the 4 potentiometers and solder 4 input and 4 output wires¹⁸.
4. Attach the "Safiros Mux 16" board, soldered with 10 pins, onto the program selector pads¹⁹.
5. Put the x9 board back in the enclosure, screw the potentiometer and audio socket nuts, attach the buttons, close and screw the lid¹⁰.

The kit includes a self-adhesive tape printed with the original program names for each x9 pedal¹.

If you would rather not solder, Microdesignum offers an install service in which you send them your x9 pedal and they fit the module, which is included in the price, with supposed availability of 28 days⁴. Partners in the USA, Canada and France can also provide the install service, at prices and shipping costs that may differ⁴. Microdesignum also sells an EHX Mel9 with MIDI control already installed¹¹, and the module pages for the Compact and Rack versions list the same target pedals¹⁵.

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