Earth Sound Research bass and guitar amplifiers were made by Instrument Systems Audio Corp based in Farmingdale, New York, first introduced in 1972. They were a division of Benjamin Electronic Sound Corp, and also made PA mixers/power amps, keyboards and stand alone reverb units (solidstate) as well as distortion and volume pedals. The early Earth tube amplifiers were based on Fender designs with later solid state ones were based on Peavey designs.

The Earth Amplifiers brand was revived by a Netherlands boutique amplifier manufacturer, which circa 2017 offered handcrafted guitar amplifiers, effects and cabinets.

Source: Earth Sound Research amplifiers catalog 1972-1975

Source: Earth Sound Research amplifiers at Pedal Heaven (4 April 2017)

Source: Earth Amplifiers website (4 April 2017)