Building the YaVCF filter

Building the YaVCF filter

Note that these instructions apply to the partially built, 6HP version of the module with SMD components. It is not applicable for the old 100% PTH version of the module (that's at https://github.com/yorkmodular/yavcf) - these instructions can also be followed to build the forthcoming 4HP version of the module.

All surface-mount components have been pre-soldered - it is up to you to provide the necessary through-hole componentry to complete the build. These are updated boards which have been fabricated by a PCB assembly service.

The following components will be required:

  • 4x PJ301M(-12) jacks (aka. THONKICONN)
  • 2x red LEDs (D1, D2) for the feedback section - the square pad is the LED cathode.
  • 2x 2N3906 PNP transistors (Q1, Q2) - matched pairs aren't necessary. You can use any suitable PNP transistor, but 3906s are probably the easiest to get.
  • 3x 1nF film capacitors (C2, C5, C8) - you could use ceramic caps but it will likely change the character of the filter. I tend to use Mylar capacitors on pre-built modules - you can use polypropylene if you want to go for full overkill.
  • 1x 220nF film capacitor (C1) - same caveats as above. This is a DC-blocking capacitor.
  • 2x 10uF electrolytic capacitors (C9, C11) - note the polarity!
  • 3x Alpha RK097 (or equivalent) pots - 100k linear taper recommended.
  • 2x5 IDC header - the white line on the silkscreen aligns with the -12V line.

The schematic is shown below - crossed out components represent items that need to be provided and fitted by you, as listed above (right click + open in new tab to see the full size version)

It should be obvious what goes where - the only real gotchas are the polarities of the two decoupling caps, C9 and C11 - look for the small '+' by the component footprint and put the longer lead of the cap through it. Generally, electrolytic capacitors will have the negative side denoted by a vertical band on the capacitor body.

Whatever you do, solder up the power connector before you solder the jacks in place, otherwise it will be almost impossible to solder the power connector without damaging the bodies of the jacks (don't ask how I know this - muscle memory is a bitch). 

Other than this, components can be fitted in any order.

How to use it? Put an audio signal into the LP IN or HP IN jacks (or both, if you're feeling adventurous), put the output from an envelope generator or LFO into the CV IN jack, connect the output jack to something suitable and twiddle the knobs until you find a sound you like.

The CUT pot controls the cutoff frequency of the filter, the RES pot adjusts the resonance setting (the filter will self-oscillate - you'll see the LEDs start to light up when this happens) and the CV LVL pot adjust the amplitude of the incoming control voltage - more CV means greater chance of resonance happening.

TL;DR - just twiddle the knobs.

Easy peasy.

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