Building the Pedal IO

PCB and Schematic:

Latest PCB:

PCB is green and is labelled “REV = D”

Use the values listed on the PCB, and not in the BOM (below).


Source 1
Source 2
2100nCapacitor0603Note Package! Unlabelled on PCB
21kTrim Pot6mm top adjustment.
1B10kPotentiometer9MM SNAP-IN9mm vertical snap-in pot, Alpha / Panasonic style with 6mm built-in knob.
2M7DiodeDO214AA1n4007 or equivalent
4THONKICONN3.5mm Audio JackTHONKICONN3.5mm socket for Eurorack modular synths
1Tile Tail"Futaba J" Tile Tail.
2TL072SO08Almost any dual opamp can be used.

PCB Corrections:

PCB version “VCOTiles28″only:

Cut the trace between the capacitor and middle lead of top trimmer. The cut is displayed as a red line on the PCB diagram above.

When all components are added, solder a wire between the other side of the capacitor and the middle trimmer lead (shown in orange on PCB diagram above.)


  1. Clean the PCB with Isopropyl Alcohol.
  2. Solder the surface-mount components to the PCB.
    1. Begin with resistors and capacitors.
    2. The small unlabelled footprints (0603 size) are 100n capacitors.
    3. The two large unlabelled footprints near the power header are M7/1n4007 diodes. Make sure the polarity is correct.
    4. Finally, add the OpAmp, making sure it’s in the correct position (pin 1 is by the large white dot).
  3. If using hot-air or an oven to solder the surface-mount components then do this now.
  4. Inspect all of the soldered components for solder bridges between pins and components, especially around the OpAmp.
  5. Solder the two trimmers.
  6. Solder the Tile-Tail power lead. Trim the exposed front-side ends if they interfere with the jacks.
  7. Solder the front components (pot and four jacks). It’s a good idea to put the panel on before soldering to make sure they are aligned.
  8. Again inspect all of the soldered components for solder bridges between pins.


Check that there’s no continuity between the red, white, and black wires on the power lead. If there is continuity then for shorts between the components around the power lead and diodes.

Check that there’s no continuity between the both ends of each of the small 0603 capacitors, located near the OpAmp. If there’s continuity then check all of the soldered connections for shorts.

Plug the module in and test all functions.