Countryman was most recognized for designing a number of complex and effective microphones for performance.

[2] Countryman engineered a number of devices that enabled the multimedia and psychedelic art scenes of the 1960s and 1970s.

[5][6][7] The pickups worked similarly to condenser mics, allowing the musicians to produce "truly brilliant" sound compared to microphone amplification, according to Owsley Stanley.

[9] The technology, developed for the Grateful Dead, became a part of many musical performers' rigs.

[9] Other custom amplification included a clavichord pickup built for keyboardist Jim Lowe.