Briefly, the 258D is a 2 layer board, similar in concept to the 258V/J - i.e. the Electronotes option 3 expo converter and triangle core with 258-like waveshaping, plus a few tweaks for better tracking and stability, a calibrated 1.2V/O input, and a buffered copy of the triangle core on the rightmost output of each osc. Saw/Square waveshapes are selectable per osc, but I have left this as a behind the panel option as recalibration of the waveshape control is required after changing.
The 281D is a four layer board, and I believe the first single board implementation of the 281. It's broadly similar to the original circuit but has correctly implemented auto-start when entering cycle mode, buffers on both CV and pulse outputs to improve behaviour when stacking CV outs to multiple destinations and when stacking multiple pulse outs together to create unpredictable/non-repeating poly-rhythmic pulse sequences. There is an option to implement the transient/sustain behaviour either the original way for use with Buchla pulse/gates, or using Dave Brown's transient mod if using with standard gate signals. There's also some general tidying up around the logic/control circuit.
Here's what I've tried to bring to the table:
- Known good designs - I have built multiples of both modules and spent a lot of time testing and verifying their operation and builadbility, so there are no nasty surprises waiting for anyone attempting to build either of these.
- Comprehensive, publicly available documentation - each project has a github repo with full documentation, available from day one. KiCad project files, PDF schematic, BOMs, interactive assembly guide, build options/calibration procedures, etc.
- Predominantly SMT construction, excluding connectors and panel controls. I much prefer working in surface mount these days. The parts are cheaper, assembly is faster, and in addition this means there are no obsolete parts in either build.
- Component designators you can still see after populating the boards - probably needs no elaboration, but in the event that any troubleshooting of a build is required this, along with actually having documentation, is fairly critical
- Boards fit with any panel based on the EMS drill files (though the 258 will need the hole for the scale trimmer drilled out if you're using an existing panel.)
Github links for your perusal:
All comments and queries are welcome.
Now, the caveats: as indicated in the notes, although I've made every effort to make sure hand assembly is doable, these aren't necessarily recommended as a first SMT project. The build notes are very much a guide, not intended to hand hold you step-by-step through soldering each component - some common sense will be required, though if anyone thinks I have missed anything critical, please let me know. For the most part these are SOIC/0805/SOT-23, the smallest part on both boards is a SOT-363 package which is comfortably hand workable.
It would of course be remiss of me not to mention that I have a few boards of each for sale (281 currently sold out but more are on the way) - Julian at http://thebeast.co.uk will also have boards in his store shortly so you can order the PCB and a panel from the same place - he will also have 258D panels specifically for these boards. I will also shortly have a handful of each module pre-built in case SMT isn't your thing. I'll keep the "sales pitch" to that, primarily I would just like to get these out into the world and, I hope, add something useful to the DIY side of things.
Moderator addition by Kent
Be sure to keep the build discussion confined to the threads in the DIY section:
281D Build Thread.
258D Build Thread
This thread can be used as an announcement, advert, and celebration of sorts but tech stuff should go in the aforementioned DIY thread. We normally don't allow cross-posting of very similar material across sub-fora, as it gets confusing and messy for users as thread expand. The mods also get accused of having deleted posts when they are actually perfectly fine, but in another thread. We'll allow this and see how it goes as the topics are slightly different.