Imp – MIDI Upgrade

The Imp is a MIDI upgrade for guitar, bass or other effects devices. With the Imp it is possible to switch an effects device on and off with MIDI control, to change the channel or sync the tap tempo to MIDI clock. The normal functionality is not restricted. On the contrary: old, loud and sluggish 3PDT switches are being replaced by a modern, quiet, relay-based soft switch. The true bypass functionality is retained.

This results in almost endless application possibilities. The beloved, old vintage overdrive pedal that should somehow be added to the MIDI setup. The old delay that should be synchronized to MIDI clock. The one pedal for which there is no loop left, or the multi channel preamp that should change channels via MIDI.


  • MIDI controllable bypass, or tap tempo
  • MIDI clock synchronous switching
  • MIDI channel can be set using the switch
  • Compatible with all MIDI 1.0 compliant controllers
  • True bypass relay circuit (only Imp-3PDT)
  • Effect monitoring for reliable status (on/off)
  • Simple assembly through soldered-on sockets (Socket assembly only)
Imp-3PDT loose assembly and Imp-SPST socket assembly
Imp-3PDT loose assembly (l.) and Imp-SPST socket assembly (r.)


Upgrading 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 the conventional 3PDT switch.
Imp-SPST: For effects that already have an SPST soft switch for bypass and / or tap tempo.


The Imp-3PDT variant replaces the 3PDT true bypass switch with a MIDI-controllable, relay-based, SPST soft switch. In regular effects devices with 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.

Effects device before Imp-3PDT installation
Effects device before Imp-3PDT installation

To install the Imp-3PDT, the 3PDT switch is removed. The signal is then passed true bypass through therelay of the Imp. The Imp is then controlled with both MIDI and an SPST.

Effects device with installed Imp-3PDT
Effects device with installed Imp-3PDT


The Imp-SPST variant uses an existing SPST soft switch and its control electronics (which can be e.g. a microcontroller and a relay – marked with CTL in the picture) and takes over the control, triggered by the switch, or MIDI.

Effects device before Imp-SPST installation
Effects device before Imp-SPST installation

The original SPST is retained upon installation. The Imp is installed between the SPST and the effects device. Effect devices with SPST and relays often do not remember the switching status after switching off (e.g. Earthquaker Devices). The Imp solves this problem as well and remembers the switching status after powering off.

Effects device with installed Imp-SPST
Effects device with installed Imp-SPST

In addition, the Imp-SPST has a monitoring of the already existing control electronics. This guarantees that the correct state is switched at all times and not just a simple toggling is implemented.

The Imp-SPST is configurable and can handle almost any effects device.


Socket Assembly

The preferred mounting variant is socket assembly. The MIDI sockets (Mini-TRS Type A) are soldered onto the Imp and the Imp is then mounted securely and stably using suitable drillings in the housing. This variant is ideal for cases that offer space for a 9V block in the area of the switch (e.g. many EHX and Earthquaker pedals).

Imp-3PDT in Electro Harmonix Muff Overdrive
Imp-3PDT with socket mounting in an Electro Harmonix Muff-Overdrive
Imp-SPST in Acapulco Gold
Imp-SPST with socket mounting in an Earthquaker Devices Acapulco Gold

Loose assembly

Even if the socket assembly can cope with any thermal and mechanical loads due to its stability, many effects have no space, or the position of the sockets on the underside is not desirable. In this case the Imp can be placed loosely in the housing.

To avoid short circuits, the Imp can be packed in a piece of suitable shrink tubing. This is also available in the shop.

In order to conform to the MIDI standard, the sockets used must be isolated from the housing. Isolated mini TRS sockets are available in the shop.


An additional SPST switch is required for the Imp-3PDT. This has to be Normally Open and can of course also be ordered in the shop.



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

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
SpreadsheetConfiguration Helper (Imp-SPST only)English
InstallationImp-3PDT and Imp-SPST – 1.1 (June 2021)English | German