@futurebird
I've had lots of enclosures like that! For power supplies and high voltage ampliers (to drive a piezo-electric actuator) or analog voltage adders and mixers...
I work with lasers, and have needed to build little servo systems to control them, or to control the interferomers or optical resonators I use them with.
You could buy some cheap lasers like these...
https://www.ebay.com/itm/134987089639
... and try to build your own current and temperature controllers for them...
Then you could also use them for experiments like spectroscopy (on little sealed tubes of iodine vapor) or measuring the refractive index of water, or interferometry... And you'd need some analog control electronics for that stuff.
Sometimes we build "noise eater" circuits in boxes like that - negative feedback loops to cancel out laser intensity variations. I suppose you could also build your own noise-canceling circuits for headphones. They work the same way.