Built this recently
https://oshpark.com/shared_projects/wLhDZUDMStereo fixed gain unbalanced in/out on 1/8" mini connectors. Still need to tweak the layout a little bit since connectors don't sit right, but it works and sounds really good. No mic power on board, works with a 9v pp3, designed for use with battery-powered microphones (cmbi's for me). The ic was socketed and I tried it with both Max412 and LME49720, both sound good, the 49720 maybe a little better. I could have actually gotten this a lot smaller but since it was a first attempt I didn't know how small I could handle with the iron. Next time I'll use solder paste and not be afraid of soic packages.
Something similar could easily be adapted for use with dynamic microphones with an inamp, but I have none currently.
Thinking about doing a 4 channel version in maybe 1/3rd more space which would make it very compact, but only for specialized applications.
I don't want to get into a situation where people are asking for pip or this or that, but I would like to make it available for people to do what they want with it. A 4 channel could easily sit in an altoids tin, maybe even 6 channel.
Also have on my mind doing a transformer input version. Lundahl has small input transformers, trannies and stereo preamp both will fit in an altoids tin. Yet another idea was a ghetto altoids modular 6 channel 1) pre 2) mixer. This is probably too much brainpower but who knows. If I can find a small usb battery, maybe altoids size or slightly larger that can power everything including phantom then I might devote some time to the modular idea.
It was sort of an experiment to see if it would sound better than the Sony M10 preamps, and that it did by a large margin.
(Schematic credit to Ricardo of Micbuilders)
pics added. If you look close there's no ic on the board, because this is a different design (aka fail), but they are about the same size.
wrapped in saran, packing tape, then copper foil.