AmpRx is a Nashville, Tennessee-based company that designs voltage optimization equipment for tube amplifiers. The brand is owned and operated by CEO Cassandra Sotos, a touring violinist with an industrial engineering background, and President Clark Singleton, a bass player and drummer who handles unit construction at the company's TuneSquad studio facility. Both founders come from professional musician backgrounds, and the company positions itself as a tool maker for working players and studios.

The flagship product is the BrownBox, an adjustable AC power supply that lets users dial in the wall voltage feeding their gear — a workaround for the fact that modern wall outlets often run hotter than the voltage many vintage tube amps were designed for. The lineup also includes the Brownie, a smaller voltage controller that can both raise and lower incoming voltage, and the BackLine 2400, a higher-capacity power station aimed at multi-amp rigs and backline setups. The products are commonly used with vintage Fender, Mesa Boogie, Ampeg, and other tube amplifiers where running at original spec voltage is considered key to tone and tube life.

AmpRx has been publicly endorsed by Dr. Z Amplification, and the company highlights working guitarists such as Mike Harris of Old Crow Medicine Show, Ricky Paquette of The Sheepdogs, and Italian rock guitarist Diego Leanza among its users. The brand sells direct through brownbox.rocks and through dealers including Sweetwater, American Musical Supply, Humbucker Music, and Sonic Circus.

AmpRx has 5 products cataloged on Equipboard, including Guitar Power Attenuators and Audio Samplers. Their gear is featured by 12 artists, with the strongest followings in Rock, Folk, World, & Country, and Jazz. Notable users include Daron Malakian, Chris Stapleton, and Derek Trucks.