TS-1 is a digital synthesizer based on a Teensy 3.2. In the original, on the site https://www.notesandvolts.com/, it is created with a multiplexer that queries the 15 analogue potentiometers. A Teensy 3.2 has 20 analogue connections and I wondered why you need a multiplexer. It is not needed. So I adapted the code a bit and changed some unpleasantness. I am a software developer and such things are particularly noticeable. Without a multiplexer, it is easier to query the individual potentiometers in an array with a structure.
Here is the modified Schematics
I have also created a PCBwith ExpressPCB, and here again as a PDF.
I use a TEKO 363 enclosure and created the front panel with the free Front Panel Designer from Schaeffer. Here is the front panel as a PDF file Front.pdf.
Here is a video with my first test after finishing the synthesizer:
Finally, the INO file with the sketch.