Designing and troubleshooting a module | Instruō - ceithir

video upload by Instruō

"Hello and welcome!

👉 • Instruō - ceithir | Project Overview
(Here is an introduction to the ceithir with more detailed project background and sound examples.)

In 2015/16 Instruō began as a video project. Specifically a time-lapse of me designing the original troika module.
Ten years later, I’ve returned to that idea with ceithir, a winter holiday project I designed with video documentation in mind.

This video shows the process of ceithir's initial prototype design.
The full module interface was the first part of the process. That stage has its own video feature:
• Designing a Eurorack Module interface | In...

In this first hardware iteration I focussed on the core functionality of a single channel version of the filter. The majority of the circuit was tried and tested in the I-ō47 module. But I made several additions to the design for ceithir:
Temperature compensation of the core
Dedicated oscillator mode with stable peak amplitude
Stereo output utilising modulated phase shift to create discreet L/R
Additional mode morphing to incorporate band-pass response

I forged ahead with a hardware design where priority was not placed on manufacturability of the prototype. It is a two board layout requiring circuitry distributed between two parallel PCBs. This used many header connectors but provided a large "canvas" to lay out all elements of the circuitry in a sectional way that allowed for ease of navigation when it inevitably came to troubleshooting and fixing mistakes/making refinements.

The main section of this video was recorded after building and testing the first prototype. I circuit bent the prototype and refined the circuit to confirm the behaviour I intended. I then recorded a session logging all the changes made comparing between the hardware modifications, schematic updates/annotations and demonstrate circuit simulations of the updates.

It's a very hands-on and satisfying process! but a referencing session like this is important to document all changes and modifications made. I am not great at taking notes as I go and I often end up with a collection of voice notes and scattered notes. Having a camera rig and screen recording set up was very helpful for comprehensively documenting all confirmed changes.

The latter part of this video is footage predating the main vlog. It is time-lapse recording spanning the 28th to 31st December 2025. (I designed the full interface earlier in that week).
I recorded some commentary voice over for this video edit where I describe various steps shown on screen.
The time-lapse footage is abridged because it ended up too long to be practical in this video.

The two programs I use in this video are Adobe Illustrator for all graphical design work, and EagleCAD for component layout and placement.
I now use KiCAD for all my actual PCB design, but I’ve used Eagle for so many years during this stage that, as clunky as its interface is, I’ve built a lot of ingrained muscle memory navigating it for component placement experiments.

Please feel welcome to join the Instruō Discord server.
It’s a growing community that shares creative ideas, technical support, and general chat. It’s becoming a really nice place to share projects like the ceithir.

I hope you enjoy!
Cheers
~Jason"


00:00:00 Instruōduction
00:03:58 Prototype modification recap
00:04:59 First modifications - Limiter switch rerout
00:06:18 Limiter gainstage values
00:06:54 R41, R43 schematic notes
00:08:14 Oscillator mode series impedance switch insertion
00:09:27 Bi-polar frequency control for future parallel filter control
00:13:36 Bi-polar pot hardware modifications
00:15:39 Pitch control schematic notes and modification tour
00:17:39 Oscillator Mode frequency match compensation switch/trimer
00:20:13 DG switch reroute for Oscillator Mode 1V/octave tracking compensation
00:23:54 I spot a mistake!!
00:26:42 circuit value tweaks
00:28:04 Back in time to the CAD design of this prototype
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00:28:08 Time-lapse begins! Gain Cell/Filter core design
00:29:22 PCB routing ...already
00:30:20 strategic component placement
00:30:32 Pitch control circuitry
00:31:32 Resonance and Strike
00:32:36 Routing - Single side as much as possible
00:33:20 Completing feedback circuitry
00:33:59 Placement mirroring trick
00:34:22 Adding hardware
00:34:35 Illustrator time (Faceplate)
00:35:07 Crosfader circuitry
00:35:37 APF
00:35:57 LFO
00:36:14 Switch circuits
00:36:50 Trimpot placement
00:37:06 More of the same placement
00:38:11 Circuit block placement
00:38:40 Pin header placement
00:39:41 Pin header mapping
00:40:20 Nudging things around
00:41:21 PCB layout vs. Schematic capture
00:42:29 Faceplate conversion