Building Benjiao Modular’s Eurorack MiniMix Module

Goal

  • Every eurorack system needs at least one mixer and I don’t have any
  • Order a known good PCB from an online supplier
  • If successful, I’ll have the KiCad project, PCB, and front panel as references for future projects, and I’ll know a reliable supplier for PCB manufacturing.

Status

  • 95% Complete
  • Replace incorrect power filter capacitors with 22 µF parts
  • Find some knobs for the slider shafts

References

Progress

2026-05-05 Built a Second Module

Rinse and repeat. I now own 2 mixers!

2026-04-26 Testing

This was where things got semi-interesting.

As the pots weren’t throwaway cheap, I figured I’d test one channel before fitting an entire module’s worth.

And as my eurorack bench power supply project is still in development, with the breadboard version hooked up to a different module that’s also still in development, I chose to use my actual modular system to power the new module. In the cold light of day, this was not a great decision and, whilst nothing went wrong, the balance of risk and reward was way off.

First, I did a simple power-up to check that there was the right amount of power everywhere I expected. An op-amp immediately started smoking. I’d soldered it in upside down.

After a quick switcheroo I routed Braids through the mixer, with the oscilloscope connected before and after MiniMix. Things looked almost right, but not quite. Tracing the signal through, the DC coupling capacitor C7 ( circuit ) seemed to be doing something odd to the signal. I bypassed it and all was well so I substituted C7, C5, C6 and C10 with links.

The more I think about this, I feel like something else may be going on and further analysis would make a good article for the site.

2026-04-25 Populated a PCB

No dramas here. The circuit is pretty straightforward, so everything went together quickly.

With all the components in place, I checked continuity against the schematic. Always a vital step as I found a dry joint on an op-amp pin.

2026-04-20 Ordered Components

Given that I was working to a PCB that was already laid out, I needed to ensure that the components I ordered would all fit - in particular the sliders. After searching around, I ended up getting everything from DigiKey as they stocked the 45mm travel, 100k Bourns sliders.

Unfortunately, I ordered the wrong value capacitors for the power supply filters - 0.22uF, rather than 22uF.

2026-04-14 Ordered PCBs

For previous projects, I’d used OSHPark but this time around I quite liked the look of JLCPCB . Cost was surprisingly low and turnaround was really quick. I ordered the minimum of 5 PCBs.

Outcome

  • Module functions correctly despite the missing power filter capacitors
  • JLCPCB delivered good-quality boards
  • The design was straightforward to assemble
  • I made a couple of avoidable mistakes during assembly and testing
  • I’d happily build another one