PCB and Schematic:
|3||3.5mm Audio Socket||THONKICONN||3.5mm socket for Eurorack modular synths||http://shop.erthenvar.com/collections/accessories/products/3-5mm-inline-jacks||https://www.thonk.co.uk/shop/3-5mm-jacks/|
|1||LM13700||LM13700M||SO16||Dual OTA with buffers.|
|2||Diode||M7||SMA||Power diode (1n4007)||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|
|2||B100k||Potentiometer||9MM SNAP-IN||9mm vertical snap-in pot, Alpha / Panasonic style with 6mm built-in knob. Audio taper.||http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/logarithmic/1m-ohm-logarithmic-taper-potentiometer-round-knurled-plastic-shaft-pcb-9mm.html|
|1||100R||Resistor||0805||On back of second PCB|
|1||Opamp||TL072||SO08||Almost any dual Opamp can be used|
|1||5.1V||ZENER Diode||SOD-123||Zener Diode SOD-323|
|1||Tile Tail||"Futaba J" Tile Tail.||http://pulplogic.com/product/tile-tail/|
- Clean the PCB with Isopropyl Alcohol.
- Solder the surface-mount components to the PCB.
- Begin with resistors and capacitors.
- There is a single 100R resistor on the back of the interface PCB (sorry – best place for it).
- The small unlabelled footprints (0603 size) are 100n capacitors.
- The two large unlabelled footprints near the power header are M7/1n4007 diodes. Make sure the polarity is correct.
- Finally, add the OpAmp and LM13700, making sure they’re in the correct position (pin 1 is by the large white dot).
- If using hot-air or an oven to solder the surface-mount components then do this now.
- Inspect all of the soldered components for solder bridges between pins and components, especially around the OpAmps.
- Solder the Tile-Tail power lead and 3-pin BP LP header.
- Add the male and female PCB connection headers. It doesn’t matter which PCB get the male or female headers, just that they’re on the opposing. The sides with the surface-mount components face the same direction (downwards when module is installed), and the PCB with most of the components is on the “bottom”.The top of the left header needs to be trimmed flush to the PCB after soldering so it doesn’t interfere with the jack.
Alternatively, only male headers can be used to connect the PCBs together permanently, but troubleshooting will be more difficult if there are problems.
- Solder the front components (pot and jacks). It’s a good idea to put the panel on before soldering to make sure they are aligned.
- Again inspect all of the soldered components for solder bridges between pins.
On the first PCB revision there can be a “thump” if the CV voltage goes below 0V. This can be mitigated somewhat by adding a 1uF capacitor to ground to the CV input on the LM13700.
This “dethumper” is already added to the latest revision (see schematic).
Be careful that other nearby components aren’t inadvertently shorted.
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.