Building the LFO

PCB and Schematic:

Latest Revision D PCBs (labelled on front of PCB) use a A100K pot instead of a A1M pot. Some parts values are different: 1u capacitor instead of 100n; 47k resistor instead of 680k; 0R resistor instead of 1K. The PCB is labelled with the correct values.


Source 1
Source 2
33.5mm Audio JackTHONKICONN3.5mm socket for Eurorack modular synths
1A1MPotentiometer9MM SNAP-IN9mm vertical snap-in pot, Alpha / Panasonic style with 6mm built-in knob. Log taper.
4100nCapacitor0603Note package size! Not labelled on PCB (only small package).
31n4148Signal DiodeMINIMELFDIODE
15z15.1V Zener DiodeSOD323DIODE
21N4007Power DiodeSMAAlso called "M7" in this package.
112KResistor0805Tapering resistor. Only install if using linear taper pot.
1 Tile Tail"Futaba J" Tile Tail.
2TL072TL072 Dual OpampSO08Almost any dual Opamp can be used.


  1. Clean the PCB with Isopropyl Alcohol.
  2. Solder the surface-mount components to the PCB.
    1. Begin with resistors and capacitors.
    2. If using a A1M (log/audio) potentiometer (recommended) then don’t install the 12K resistor (in a white box).
    3. The small unlabelled footprints (0603 size) are 100n capacitors.
    4. The two large unlabelled footprints near the power header are M7/1n4007 diodes. Make sure the polarity is correct.
    5. Finally, add the OpAmps, making sure they’re 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 OpAmps.
  5. Solder the Tile-Tail power lead. Trim the exposed front-side ends if they interfere with the pot.
  6. 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. Some pots have a metal support underneath — check that it doesn’t short the power lead pins. Cut the leads flush to the PCB if they are.
  7. 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. All three outputs should be shaped properly and oscillate between 0 and 5V, plus or minus 100mV.