Audio Research D 75 (1975)

The Audio Research D 75 is a vacuum tube stereo power amplifier introduced in 1975 as a smaller, more affordable companion to the company's D150. It was positioned as an entry point into high-end audio, with a retail price of $495 at launch. That price made it notable in its day. The original The Absolute Sound review, later reproduced at Dagogo.com, called it a "breakthrough product" and a "poor man's D150," and praised its performance as unmatched at the price.

The amplifier delivers 75 watts per channel in Class AB, with a 15-watt Class A region. The tube lineup is four 6CA7 output tubes per channel, a shared pair of 6FQ7/6CG7 driver tubes, and two 6DJ8 input tubes. The input stage is a fully balanced differential circuit. The power supply is a hybrid: solid-state regulation for the input and driver stages, tube rectification for the output stage. Output taps are provided for 4, 8, and 16 ohm loads. Frequency response is rated at ±0.5 dB from 20 Hz to 20 kHz, signal-to-noise ratio at 105 dB referenced to full output, and damping factor at 20:1. The chassis measures 19" W x 5.5" H x 10" D and weighs 40 lbs. The front panel is minimal, with only a rocker power switch and a small LED indicator.

The period review found the D75 offered "remarkable musicality and transparency" for its price. It noted that the D75 lacked the ultimate bass weight and dynamic slam of the D150, but was "far more refined and musical than most solid-state amplifiers of the era." The reviewer called it "very quiet, very smooth, and very musical," and described it as one of the finest amplifiers heard at any price.

A note on sourcing: all of the above comes from a single reproduction of the original The Absolute Sound review. No second independent source was located in the research. No current market prices, common maintenance issues, or spare parts availability are documented.

Power output: 75W/ch (Class AB), 15W/ch (Class A)
Tubes: 4 x 6CA7 output per channel, 2 x 6FQ7/6CG7 driver (shared), 2 x 6DJ8 input
Output taps: 4, 8, 16 ohms
Input sensitivity: 1.5V for full output
Frequency response: ±0.5 dB, 20 Hz–20 kHz
S/N ratio: 105 dB (ref. 75W)
Feedback: 12 dB global
Dimensions: 19" W x 5.5" H x 10" D; 40 lbs.