Recently I've started using a Mackie "Big Knob" to control the level of my tuning signal input into the system processors, and the level of the walk-in music if it's running straight into the processors. You can see it next to my laptop on the photo below:
It worked really well and I really liked it in my workflow, but the big knob is a very large and heavy box for how much it actually does. I started looking into smaller options, but couldn't find any that really did what I wanted without requiring an external power supply or lots of Jack adapters. Most are designed for studio use, rather than touring, so space is much less of an issue. So ultimately I did what any bored engineer would, and decided to build one myself.
I found this article discussing how to use an Alps Alpine 10k Log potentiometer and some switches to create a basic studio monitor controller, and decided to order some parts and mock up a design.
I wanted a mono XLR input that would connect to my measurement soundcard, a stereo minijack that I could use to play back tracks or walk-in, and a stereo XLR output. I'd need a switch to select the required input, and a potentiometer to control the level.
Some quick soldering later and I had a prototype! It worked well when connected straight to the balanced inputs of an LM44, but the volume didn't function correctly when feeding the unbalanced inputs of my home stereo. As I'm pretty much always going to be using this with balanced systems, I can live with that.
Next I needed a box to put it in, and in order to keep everything as small as physically possible, I decided to 3D print it, and the design I made and used is here and shown below:
Once it arrived there were a few issues to be faced - extrusion 3D printers tend to be very accurate horizontally, but can vary vertically, and in this case my design was squished vertically very slightly, which was okay for the most part but made the case slightly too small for the potentiometer, so I needed to modify the lid slightly. Additionally the 2 tabs I added to hold the cover in place broke off very easily so I ended up gluing the housing together once I was happy.
Yet to be road-tested, but I'm generally very happy with it so far. I'd like to come up with a design that works properly with unbalanced systems, but this is perfect for my needs at the moment.