Building the LFO

PCB and Schematic:


BOM:

Qty
Value
Device
Package
Description
Source 1
Source 2
33.5mm Audio JackTHONKICONN3.5mm socket for Eurorack modular synthshttp://shop.erthenvar.com/collections/accessories/products/3-5mm-inline-jackshttps://www.thonk.co.uk/shop/3-5mm-jacks/
1A1MPotentiometer9MM SNAP-IN9mm vertical snap-in pot, Alpha / Panasonic style with 6mm built-in knob. Log taper.http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/linear/1m-ohm-linear-taper-potentiometer-round-knurled-plastic-shaft-pcb-9mm.html
4100nCapacitor0603Note package size! Not labelled on PCB (only small package).
1100nCapacitor0805
21uCapacitor0805
31n4148Signal DiodeMINIMELFDIODE
15z15.1V Zener DiodeSOD323DIODE
21N4007Power DiodeSMAAlso called "M7" in this package.https://octopart.com/search?q=rectifier&start=0&category_ids=4226&specs2.2.values=SMA&specs2.330.numbers=(50__200)&specs2.313.numbers=1&sort=median_price_1000&sort-dir=asc
1100KResistor0805
310KResistor0805
112KResistor0805Tapering resistor. Only install if using linear taper pot.
41KResistor0805
1220KResistor0805
12KResistor0805
233KResistor0805
13KResistor0805
147KResistor0805
1680KResistor0805
17K5Resistor0805
19K1Resistor0805
1 Tile Tail"Futaba J" Tile Tail.http://pulplogic.com/product/tile-tail/
2TL072TL072 Dual OpampSO08Almost any dual Opamp can be used.

Assembly:

  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.

Testing:

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.