When I was performing at the fair last week and had to deal with a sound system that only had one line in, I managed to make it work. I ended up using the Zoom recorder that I use for podcasts as the mixer. That’s a decent emergency solution, but I’d rather not have that expensive recorder cooking in the sun all day.
I ordered this little audio mixer and it seems to work well so far at home.
It’s not much bigger than two decks of cards and can run off of USB power. It’s got four channels, which is one more than I need. I haven’t tried it in a live show yet, so I don’t know how well it will work in the real world, but I’m hoping it’s a good solution!