Stax DA-300 (c. 1975–1980)

What survives on the Stax DA-300 is mostly Stax's own advertising, and the ads made big claims. The DA-300 was the company's flagship Class A power amplifier, introduced in a 1975 print campaign that paired it with the SRA-12S all-FET preamp (then $500) and the SRX III electrostatic headphone system (then $230). Audio (October 1975, p.47) carried that campaign, as did High Fidelity (September 1975, p.113). Stax's copy called it the world's finest power amplifier and suggested asking anyone who had heard it on the world's finest speakers.

The concrete specification behind the hype: 150 watts RMS per channel of pure Class A power. By 1978 Stax was advertising a revised DA-300(a), grouped with the DA-80 and DA-80M mono amplifiers, claiming faster slew rate, better transient coupling, and IM/HD below 0.007% at 20 kHz; the company presented the line as the first commercial Class A amplifiers, now improved. High Fidelity (November 1978, p.23) ran this later campaign.

Independent documentation is thin — no equipment test, review, service manual, or original retail price for the DA-300 itself appears in the available record. What's known:

Class A power amplifier, stereo
150 watts RMS per channel (manufacturer's rating)
DA-300(a) revision (c. 1978): faster slew rate, better transient coupling, IM/HD below 0.007% at 20 kHz — manufacturer's claims
Advertised from 1975 through 1980