This is a Flatline Compressor, built from a madbean PCB. It's a fairly simple optical circuit, and the circuit board is small enough to cram into a 1590A case. I built one a few years ago and I like it enough that I felt I had to have another one for some reason.
Unlike my other build, this one fits into the palm of my hand!
Unlike my other build, this one fits into the palm of my hand!