Imp – MIDI Mod

The Imp is a MIDI mod for guitar, bass and other effects devices. With an Imp it is possible to switch effects devices on and off via MIDI control or handle other switching duties.

The possibilities are almost endless. Add your beloved old vintage overdrive pedal to your MIDI setup or sync your analog delay to MIDI clock. The list goes on: change the channel on multi-channel preamps, or simply turn the pedals on and off when all loops are occupied on the loop switcher.


  • MIDI controllable switching (bypass, tap tempo, etc.)
  • MIDI clock synchronous switching
  • MIDI channel is selectable by using the foot switch
  • Compatible with all MIDI 1.0 compliant controllers
  • True bypass relay circuit with momentary function (only Imp-3PDT)
  • Effect monitoring for reliable status (on/off)
  • Simple assembly through soldered-on socket or footswitch
2nd Generation Imp MIDI mod (Imp-3PDT and Imp-SPST)
2nd generation Imp-3PDT (l.) and Imp-SPST (r.)

MIDI Mod Variants

Modifying with the Imp always depends on whether an SPST (also known as a soft switch) is already built in or a 3PDT true bypass switch is to be replaced. There are two different variants depending on this:

Imp-3PDT: For effects with a conventional 3PDT foot switch.
Imp-SPST: For effects that already have an SPST soft switch for bypass and/or tap tempo.
Imp-THRU: An additional PCB to add MIDI Thru functionality or buidl your own MIDI Thru box


The Imp-3PDT variant replaces the 3PDT true bypass switch with a MIDI-controllable, relay-based, SPST soft switch with momentary function. In effects devices with a regular 3PDT true bypass circuitry, the signal is routed through the switch and – depending on the switch position – looped through the effect or to the output unchanged, like in the image below.

Example wiring of a 3PDT switch before Imp-3PDT installation
Example wiring of a 3PDT switch before Imp-3PDT installation

To install the Imp-3PDT, the 3PDT switch is replaced. The signal is then passed true bypass through the relay of the Imp, controlled with both MIDI and a SPST soft switch.

Wiring of the Imp-3PDT MIDI mod as replacement for a 3PDT switch
Wiring of the Imp-3PDT as replacement for a 3PDT switch

Since there is almost always the need for a new switch when installing the Imp-3PDT MIDI mod, it is possible to solder the Imp-3PDT directly onto a SPST foot switch. No need for additional mounting holes or adhesive pads anymore.

Depending on the application, the Imp-3PDT can be purchased with and without switch. For installation without the switch, assembly aids, like fitting heat shrink, can be found in the shop. Various MIDI sockets can also be found in the shop.

Imp-3PDT MIDI mod with and without switch
Imp-3PDT with (l.) and without (r.) switch

In the example below a 2nd gen Imp-3PDT is installed into an Earthquaker Devices Hoof v1. With the Imp-3PDT soldered directly onto a switch, only one hole needs to be drilled for the MIDI connection.

Imp MIDI mod in a Earthquaker Devices Hoof
Imp-3PDT 2nd generation in a EQD Hoof v1


The Imp-SPST MIDI mod is made for effects devices that are controlled with a non-latching SPST switch. This includes devices with a relay bypass circuit (e.g. EQD, Wampler), or a non true bypass circuit (e.g. Boss) and even digitally controlled pedals (e.g. EHX Nano/MicroPOG).

Example of a effects device wiring  suitable for Imp-SPST installation
Example of the wiring of a effects device suitable for Imp-SPST installation

The Imp-SPST is installed between the switch and the FX PCB. The original SPST switch is retained. The Imp-SPST monitors the LED of the effects device. This way the Imp-SPST can not only toggle the effect on and off, but set the effects device to a certain state.

Effects device with installed Imp-SPST MIDI mod
Effects device (r.) with wired Imp-SPST (l.)

Effect devices with SPST and relays often do not remember the switching status after switching off the supply voltage (e.g. Earthquaker Devices). The Imp solves this problem as well and remembers the switching status after powering off.

The Imp-SPST is configurable and can handle almost any effects device. The second generation Imp-SPST can even control an additional switch, like the red remote switches of JHS pedals.

Since effects devices with SPST switches retain their original switch upon installation, it wouldn’t have made any sense to make the Imp-SPST solderable onto a switch like the Imp-3PDT. Instead it can be soldered onto a 3.5″ TRS socket wired as MIDI TRS Type-A. That way only one hole needs to be drilled for the whole installation. For special applications, the Imp-SPST can be purchased without socket. You can find assembly aids, like fitting heat shrink in the shop.

Imp-SPST MIDI mod with and without socket
Imp-SPST with (l.) and without (r.) socket

In the example below a 2nd gen Imp-SPST is installed into an JHS Morning Glory v4. With the Imp-SPST soldered directly onto a socket, only one hole needs to be drilled and the Imp is safely mounted. Additionally the Remote Gain switch can be controlled by the Imp-SPST.

Imp-SPST 2nd generation in a JHS Morning Glory v4
Imp-SPST 2nd generation in a JHS Morning Glory v4


To save precious space and make the Imps as small as possible, they don’t feature a MIDI Thru. If MIDI Thru is needed, though, the Imp-THRU can be used. It splits the MIDI signal to four high speed, latency free MIDI Thrus. This is particularly useful, if more than one Imp-3PDT or Imp-SPST is to be in one effects device, or an actual MIDI Thru is desired.

Imp-THRU MIDI Thru wiring with Imp-3PDT and Imp-SPST

However, it is not limited to Imps. You can build your own MIDI Thru box with it. All MIDI connections are according to MIDI standard. I even dare to say, that you won’t find a smaller MIDI Thru solution out there.

Imp-Thru MIDI Thru PCB



Besides the installation manual for the Imp MIDI mods there is an addition to the installation manual that explains in-depth the roles, measurements and the configuration (Imp-SPST only).

User ManualImp-3PDT-2.0 (April 2023)English
User ManualImp-SPST-2.0 (April 2023)English
User ManualImp-THRU-1.0 (January 2024)English
SpreadsheetConfiguration Helper (Imp-SPST only)English
MIDI ManualImp-3PDT and Imp-SPST – 1.2 (December 2021)English | German
InstallationImp-3PDT – 1.2 (December 2021)English | German
InstallationImp-SPST – 1.2 (December 2021)English | German