Dev_LOOP is a versatile analog IO board, stereo preamp and mixer designed to interface with various DSP development boards, usually not equipped with a proper hi Z instrumental inputs, analog dry path, input level control and other features typically seen in guitar pedals.

Design goals:

  • Mono/stereo operation with versatile IO routing.
  • High input impedance: 1MOhm.
  • Adjustable input gain: -/+15dB.
  • Mixer stage can work as Dry/Wet blender or as typical Effect Level control (for delays etc.).
  • Output level control.
  • Low impedance outputs.
  • Standard 9V DC power requirement.

Typical application:

Dev_LOOP typical application


  • Typical Left/mono input, Left signal is sent to both input channels.
  • Separate mono TS jacks for Left and Right input channels.
  • Stereo TRS jack carrying both input channels.
  • Left and Right output channels summed and available on the Left Out.
  • Separate mono TS jacks for Left and Right output channels.
  • Stereo TRS jack carrying both output channels.
  • Additional test points on the PCB for easy scoping.
  • Input/output jack presence "sense" signals available on pin headers.


The construction is mostly in SMT, parts are in 0805 size and SOIC14 for the quad opamps. The Pots are ALPHA 11mm stereo PCB mount ones. I have used the stacked Cliff jacks to save the board space.

Dev_Loop Schematic




Design files are available in the github repository:

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git clone