In Kingfisher Cecilia uses a condenser on her fiddle but combines it with effects pedals. This is a bit awkward to get working, and we've been using a Soundcraft Notepad mini-mixer. Unfortunately we had some issues recently where adjusting the input gain would make horrible scratchy noises:

I thought I'd need to take the mixer apart to clean it, but a bit of looking online turned up suggestions to gently pull the knob off the face of the board, spray a contact treatment, and turn the spindle to work the treatment in. This seemed surprising to me: would this really distribute the cleaner where it needed to be? But I ordered some Deoxit 5% and followed the instructions on the can, and it worked perfectly!

Now I don't hear any noise at all when adjusting the gain.

I now have an almost full can of this stuff, so if you're in Boston and are having similar issues you're welcome to come borrow it.

(Even though the mixer is now working well Cecilia isn't planning to go back to it: she bought a Voco Loco, which is a box built for exactly this purpose. It should be more robust and reliable, with fewer knobs and switches that can get knocked into the wrong position.)