Diode ladder filter
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The ladder filter is famous for its use in moog synthesisers. It uses a ladder of diodes linked with capacitors to create a voltage controlled filter - this one allows you to replace one or all of them with natural semiconductors. This is quite a tricky one to use, but it sounds great when it does - capable of unstable bubbling and plenty of unexpected squeals at high resonance.
Arsenic Labyrinth was made using the first version of this plus a squarewave module with a volca modular. Part of the dramatic sounds this makes are down to using natural semiconductors in a feedback circuit, so their odd characteristics and noisiness compounds on itself in the signal.
The schematic and PCB has space for diodes in the feedback amplification (D7 and 8) but I never found they made any difference to the resonance, so I've not actually soldered them in yet. Partly this will be down to the voltage I'm running it at - 9V, it won't actually run at much lower voltages than this presumably down to the voltage drop across all the diodes.
Licenced under the CERN Open Hardware Licence Version 2 – Strongly Reciprocal
Inputs
- Six diodes via PCB socket connector
- Cutoff CV
Controls
- Cutoff
- Resonance
Outputs
- Audio signal
Schematic
PCB layout
