The 281D Quad Function Generator PCB is a four layer, ENIG plated board designed to replicate the functionality of the Buchla 281 module using modern construction techniques and readily available parts. It can be used with any 281 panel, but we recommend the panels available from thebeast.co.uk.
It is primarily based on the original circuit designed by Don Buchla, with the following additions/alterations:
- Improved input and mode selection circuitry – no requirement to “kick” the generators when selecting self cycle mode.
- All outputs are buffered, protecting the integrator core and passive end pulse generation circuit from the effects of loading when stacked to multiple inputs.
- End pulse outputs are designed to allow stacking of multiple outputs to a single input without affecting cycling of individual generators, allowing the creation of complex/non-repeating/polyrhythmic pulse sequences. Unlike other solutions that simply add a diode in series with the output, the 281D end pulse outputs can drive a floating input low.
The 281D is designed to be suitable for hand assembly, but it is not recommended as a “learn surface mount” starting point. You should at a minimum have a temperature controlled soldering iron with a reasonably fine point and good quality solder 0.5mm diameter or finer. Some form of magnification may be beneficial for placing and inspecting the SOT-363 packages.
Full documentation is available from https://www.github.com/DunningtonAudio/281D