As a young engineer at a radio station in New Jersey, Nick Doshi built a solid-state phono preamplifier for his employer. At a friend's house it lost a listening comparison to a Counterpoint tube phono preamp built on a modified circuit from a 1954 handbook. Doshi decided the simpler design had gotten out of the way of the music, and he says every product since has followed that lesson. His circuits stay simple and use as little negative feedback as possible. Feedback is a correction loop that compares the output with the input and fixes the difference, and Doshi would rather start with tubes that behave well on their own. He calls the tubes designed by RCA and Sylvania engineers "the most linear amplification devices." Jacob Heilbrunn of Tracking Angle describes the sound as "fast, dynamic and linear." Doshi suits listeners who want tube tone with drive, especially for records and tape.

Many owners start with one box, Doshi told HiFi Knights, usually the tape or phono preamplifier, and add the line stage and amplifiers later. If you own a reel-to-reel deck, the Evolution Tape Preamplifier is the one to try. It connects straight to the deck's playback head and replaces the deck's own playback electronics. Dave McNair of Part-Time Audiophile, a mastering engineer, played master tapes through it and through the stock electronics of his Ampex ATR-102, and the Doshi gave him a clearer top end and tighter, harder-hitting bass. For a newcomer, he suggests a serviced Pioneer, Technics, Akai or Teac deck modified for direct access to the playback head. Record lovers should start with the Evolution Phono, which has plenty of gain for low-output moving-coil cartridges and lets you set loading from the remote. With the amplifiers, try different bias settings, because Doshi says they change the sound. Jason Victor Serinus of Stereophile heard clearer contrast between violin and piano at lower settings and more bass at higher ones.

Doshi's interest in audio began at about 10, when a recording engineer played him the tape of a concert he had just recorded on a Nakamichi cassette deck. He studied physics and then electrical engineering, got his start fixing tape machines at his college radio station, and spent more than 25 years in radio and television broadcasting, including work for PBS. In 2003 a visitor who came to his house to buy a used preamplifier heard one Doshi had built for himself and asked for a copy. Doshi Audio dates its start to 2006, and its first product was the Alaap preamplifier. For years most of the customers were audio professionals and manufacturers, and Doshi calls the brand of that period the industry's "best-kept secret." The tape preamplifier began as a demonstration project for shows, and Lee Scoggins of Part-Time Audiophile titled his report on Doshi's AXPONA 2018 room "Nick Doshi Builds a Time Machine." Ken Micallef of Stereophile called the Evolution Stereo "one of the best amplifiers I've heard."