Ask HN: Where are the open source physical music production tools?

In building out a home recording studio piece by piece, I’ve had difficulties finding gear that is useful but not too out of my current price range (as I do not currently have the extra money). Even for “cheap” mixing controllers or rack effects are out of my abilities currently.

What boggles my mind is that the hardware for some of this gear is nothing new; Motorized faders have been commonplace since the mid 70’s, knobs and potentiometers have been around for a while, and to my understanding most older control boards are simple computers. Is there anyone on HN that might have domain experience in this or could direct me to someone who does?

I think making custom hardware for myself and others sounds like a nice hobby in my free time, but it seems like I am not aware of any resources that break down how to get into doing so. I have experience in basic circuit design and can read diagrams, and could stand to build back my abilities to solder from more than a decade of not using them.

I do understand that there are Eurorack synths and stuff out there, but I’m more talking about making music hardware at a small scale and making it available for anyone to build upon or learn from.