Microdesignum MIDI module for EHX x9 Compact

The Microdesignum MIDI module for EHX x9 Compact is a retrofit control module built into Electro-Harmonix x9 series pedals, namely the B9, C9, Key9, Synth9 and Mel9. It gives the pedal full MIDI control of all its functions: programs 1 to 9, the four buttons and the On/Off footswitch, plus every control knob¹. The module works by electronically simulating the turning and pressing of the pedal's own knobs and buttons, so the pedal responds to Program Change and Control Change MIDI messages¹.

Microdesignum offers the x9 MIDI control in two basic variants: Compact, for pedalboard-based players, where all the electronics sit in a special enclosure placed on top of the x9 pedal, and Rack, for rack-based players, where the x9 pedal is screwed to the rear of a 1U rack panel². This page covers the Compact module; the rack version is covered separately.

What the module does to an x9 pedal

The x9 pedals are knob-and-button machines with no MIDI of their own. The module's principle of operation is that it electronically simulates turning and pressing the control knobs and encoders, so the pedal can be driven from a MIDI controller¹. Microdesignum says the module lets a musician fully control the x9 pedals, including the ON footswitch, the program selector (1 to 9) and the control knobs, whose functions depend on the pedal (Dry, Organ, Mod and Click in the case of the C9)².

The controlled parameters are listed as all of them¹. In the install service description, Microdesignum spells out what that covers: Preset, Engage/Bypass, DRY, EFFECT, CTRL1 and CTRL2, or MOD, CLICK or ATTACK and SUSTAIN, depending on the pedal variant³. All parameters can be controlled via MIDI in real time³.

Each preset on the module contains a PGM value (the EHX program 1 to 9) and stored knob values PA1 to PA4, with the number of knobs depending on which x9 pedal variant you have⁴. Microdesignum describes SysEx as too complex for hand editing and is preparing a MIDI config online tool that lets you configure global settings or any preset from a computer using a USB-MIDI converter⁴.

Installing it: wiring, soldering and board revisions

This is a soldering job, not a bolt-on. Microdesignum states there is no drilling, only soldering and cutting off¹. The install process has a few steps: power supply, footswitch, potentiometers and program selector replacement¹. In total you solder 16 wires and one component for full control¹.

The install breaks down like this, following Microdesignum's own guide:

1. Open the pedal and prepare the box: remove the connectors, footswitch, buttons, potentiometers and program selector, then affix the controller with its double-sided adhesive tape. Microdesignum warns to attach the controller slowly and carefully, because the tape is very strong⁵.
2. Solder the power supply: 4 wires, at the +9V and GND soldering points, starting with the first 2 wires of a 6-wire ribbon cable¹⁶.
3. Solder the footswitch wires: the 1 - 6 footswitch wires in normal order if the x9 board is revision "D" or newer¹.
4. Modify the potentiometers: cut the wipers of the 4 potentiometers and solder 4 input and 4 output wires, putting more solder on the wiper pads and power supply soldering points¹⁷.
5. Attach the "Safiros Mux 16" board, soldered with 10 pins onto the pads of the programs selector¹⁸.
6. Reassemble: put the x9 board back in the enclosure, screw the potentiometer nuts and audio socket nuts, attach the buttons, then close and screw the lid⁹.

Microdesignum states the installation takes about 1 hour¹. An earlier version of the maker's install guide put it at about 2 hours⁵, so budget for somewhere in that range and check the current guide before starting.

Buying the module or the install service

The Compact module is listed at 220.00 USD for a single unit, with quantity pricing of 215.60 USD each for two and 213.40 USD each for three¹³. As of 26 October 2026 it is listed as temporarily unavailable¹, as is the rack version¹⁰.

If you would rather not solder, Microdesignum offers an install service for the x9 Compact: you send them your Electro-Harmonix x9 pedal and they fit the module, with the MIDI module included in the price³. The service targets the B9, C9, Key9, Synth9, Mel9 and Bass9³.

• Install services are provided at Microdesignum's location in the Czech Republic (Central Europe)³
• Partners in the USA, Canada and France can also provide installs, and their prices and shipping costs may differ³
• The in-house service is offered only to EU customers, because of the complicated customs process for non-EU consignments³
• Turnaround is usually 1 to 2 weeks, depending on carrier delivery times³
• Support phone: +420 608 529 016³

For players who want MIDI control of other pedals, Microdesignum makes a range of similar modules, including the MIDI module for EHX POG2, the MIDI module for EHX Cathedral and the Universal MIDI module with 4 digipots and 1 footswitch.

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