The original Kequencer got way more attention than I expected, so I’ve built another one and done a more comprehensive build report to make it easier for people to replicate.
This time round I’ve taken a much cheaper and visually more interesting route, by doing away with the front panel altogether. (This build style was inspired by sndbyte’s amazing work.) I’ve also added a fine-control pot to each oscillator to making tuning a bit easier. I cleaned up the output section a bit with a LM386 amp set up in such a way that it plays nicely with the onboard speaker, external headphones, and line-out. I don’t think this is the best way of doing things but it works. The other big change is the addition of a LM317 adjustable voltage regulator, allowing you to drop the voltage from 7V all the way down to about 1.3V, when it sputters to a stop. In some settings, you can hear the regulator in action, vibrating the audio like an LFO.
I’ve uploaded a couple of demo tracks for your listening (dis)pleasure.
Super high-res version
super high-res version
Some notes about this layout:
- Bright red = unregulated V+
- Dull red = regulated VDD
- Light blue = GND
- Magenta = uninsulated connections
- Dark blue = insulated connections
The wiring on the finished product is a bit messier than I would have liked because it was all done ‘freestyle’ – I didn’t draw up any plans until after I finished. That’s a risky choice for a perfboard project of this complexity but I got lucky. I used a lot of ribbon cables to help keep track of all the connections that need to be made 8 times over (these are marked B1, B2, etc).
The design process went something like this:
- I started by laying out all the push buttons (S1-S8) along the full width of the board. These have to be arranged in a logical order to make it playable.The push buttons all have a VDD connection so I laid a bare copper power line along the bottom of the board.
- Next I added the course- and fine-control pots (R3.1-3.8, R4.1-4.8) directly above the push buttons, as each pair of pots relates to each push button. The frequency-limiting resistors (R2.1-2.8) are in series with these pots, so they are located nearby.
- The LED’s are placed close to the pots to make it clear which oscillator is active. Each LED needs a current limiting resistor (R1.1-1.8) so they are located directly beneath the LEDs, and tied together with another bare copper power line, this time for GND.
- Having this GND line nearby meant I could add all the pulldown resistors (R6.1-6.8) next to the push buttons. This completes the lower 50% of the board, taking care of most of the interactive components.
- Next I lay out all the ICs in a line across the top of the board. Having them all in line makes powering them easy: I laid another two bare copper power lines directly underneath the chips, for the VDD and GND connections. This also gives a handy place to locate the power supply bypass caps (C3, C4, C5) as they ‘straddle’ the two power lines and can get nice and close to the ICs.
- The 4017 sequencer chip is placed at the top left, along with the 8-way DIP switch that is used to select which of the steps is active.
- Stepping rate is controlled by the next IC, a 4093 (IC3 in the schematic).
- The next two ICs are also 4093′s that are configured as 8 independent oscillators.
- The oscillators are all mixed through 1M resistors (R5.1-5.8) before being amplified by a LM386, the final IC in the row.
- The LM317 voltage regulator was an afterthought that squeezed in nicely in the remaining spare space on the board.
Questions welcomed. If you are looking for help with building one of these it would be a good idea to direct your questions to the electro-music forum, you’ll get a lot of helpful answers there.
Update: proud owner Eric Peach lays down a tune on the Kequencer 2.0