Audio Research D-79 (1979)

A high-powered tube amplifier built in the USA with a regulated power supply and forced-air cooling for sustained high-fidelity performance.

Overview

The Audio Research D-79 is a tube-based stereo amplifier introduced in 1979. It was built in the USA for audio perfectionists who wanted high-definition sound on a wide range of speaker systems. Construction uses near-military-grade components. The D-79 delivers 75 watts per channel and stays stable and clear even under reactive loads. It is known for resolving subtle sonic details, and it needs minimal maintenance when fitted with high-quality tubes.

Specifications

Power Output	75 W/C RMS at 16 ohms from 30Hz to 15kHz with less than 1% THD
Power Bandwidth	15Hz and 40kHz (-3dB)
Input Sensitivity	0.75V RMS for rated output
Input Impedance	80Kohms, nominal
Output Regulation	Approximately 1.5dB, 16 ohm load to open circuit
Overall Negative Feedback	13.5dB
Damping Factor	Approximately 8
Distortion (Intermodulation)	Less than 0.5% at 1dB below rated output
Slew Rate	Approximately 10V/µs
Rise Time	5µs
Hum & Noise (Wideband, unweighted)	more than 90dB below rated output
Hum & Noise (Line components)	more than 80dB below rated output
Tube Complement	6 x 12AX7, 8 x 6FQ7, 5 x 6550
Dimensions (W x D x H)	48.5 x 48 x 27 cm
Weight	40 kg

Design

The D-79 uses a pentode output stage run in ultralinear mode. A high-energy, well-regulated power supply drives it, with Audio Research's patented balanced and cross-coupled circuitry. Three built-in fans provide forced air cooling to manage heat in the output stage. The parts are high-reliability types, and the unit is designed so it is easy to service.

Context

The D-79 was developed in response to demand from audio perfectionists who wanted high-fidelity power amplification. It shares design lineage with other models in the 79 series. The 'A' version uses a D76A front end, the 'B' uses the D90 front end, and the 'C' (and 79C-MKII) are based on the D115 and D115 MKII designs respectively.