Dr. J is a boutique guitar effects brand co-founded by JOYO Technology and Terry Li, with engineering led by Dee Leung in Shenzhen, China. The name is a nod to Jimi Hendrix, taken from the first letter of the guitarist's name. The brand began with the Green Crystal overdrive, a circuit Leung developed for local blues players that drew Li's attention and led JOYO to back a separate, higher-tier pedal line positioned above its main range.

The Dr. J catalog focuses on compact stompboxes covering the standard tonal palette, with models such as the D-53 Sparrow bass DI/drive with tube amp emulation, the D-54 Shadow Echo delay, the D-56 Planes Walker fuzz with switchable diodes, the D-57 dual buffer/boost, the D-59 distortion, and the D-60 Green Emerald overdrive. Pedals are sold through JOYO's distribution network as well as retailers like Reverb, Guitar Center, and Musician's Friend.

Dr. J Pedals has 6 products cataloged on Equipboard, including Bass Effects Pedals, Delay Effects Pedals, and Boost Effects Pedals. Their gear is featured by 2 artists, with the strongest followings in Rock and Electronic. Notable users include David Potts and Owen Allen.