Billy Strings

At 1:45 in this video, Billy talks about how he amplifies his acoustic on stage. "There's a K&K pickup here, which I blend with this microphone. (...) There's three little transducers under there, I think, kinda just glued to the bridgeplate."

Billy Strings can be seen using the K&K Double Helix pickup in this Austin City Limits performance. The pickup is visible at 4:21 in the video.

Scale Model Guitars in Nashville also posted about it in this Instagram post, saying:

Check out this mod that I just finished for billystrings. He had already installed the K&K pure mini, and we also have an internal Shure mic which runs to the mini-XLR plate that you see at the tailblock. He wanted to take it a step further and add the K&K Double Helix soundhole pickup, connected to the output jack via a three-way toggle. I had to map and mark the bracing pattern on the top in order to locate switch position, and also added a thin maple veneer under the soundboard to stabilize the switch. Also had to cut down the switch threads and tip so it will be safe in the case. I gotta tell you that this Double Helix has changed the game. It can actually take gain pedals with much less feedback risk, sounds like a dream, and the best part..no f***ing batteries!