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I'm currently working on an analog step sequencer for a synthesizer I'm making. It has a split rail 24 V supply (so +12V, GND, -12V) and follows the Kosmo specification. The features I want are:

  • 8 steps with both gate and variable voltage outputs
  • LEDs showing step progression, as well as output LED showing gate sequence
  • Clock and reset inputs
  • Internal clock generator with variable pulse width

The design is mostly based off of Moritz Klein's 5 step sequencer design, the video demonstrating it is here. However, I've changed it to 8 steps instead of 5 and I've added an internal clock generator.

If there are any issues with this, it's most likely in the clock generator section. This is based off of this article about using a 555 timer as a sawtooth wave generator. I've added a potentiometer to modulate the frequency, and I'm using a pair of op-amps to buffer and then compare the output to a static value to turn it into a pulse wave. By changing the offset value the pulse width should change.

If you can see any issues in this design, please let me know. I'm trying to make this work as well as possible.

step sequencer schematic

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  • \$\begingroup\$ Had you considered doing this with a microcontroller with internal/external DACs going through small low-pass filters? It leaves you with a lot of timing-sensitive software to write but the principles for it are straightforward and you can experiment during its development. \$\endgroup\$
    – TonyM
    Commented Sep 24, 2022 at 7:43
  • \$\begingroup\$ @TonyM I had, but I'm doing this primarily as an exercise in schematic and PCB design, so I like this solution better. \$\endgroup\$
    – Lucas Henry
    Commented Sep 25, 2022 at 0:00
  • \$\begingroup\$ Why are you using 1N4004 rectifier diodes instead of 1N4148 switching diodes? For switching the CV, I would’ve used 4016/66 cmos switches back in the day. This avoids the forward voltage drop of the diodes. r1 is on the wrong side of D1. \$\endgroup\$
    – Kartman
    Commented Sep 25, 2022 at 2:47

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