All semiconductor driver unit that has adopted custom-made low-noise dual FET at the first stage, and for the first time in STAX driver unit history J-FET has been employed at the second stage. The output of J-FET excellent in low-noise amplification, as well as large current emitter follower circuit, brings out the full performance of earspeakers. Even the music source with many high-frequency ingredients can easily be driven. The driver unit pursues an exact reproduction of musical details.