Audio Research D-80 Stereo Power Amplifier

The Audio Research D-80 is a 70-watt stereo tube power amplifier that draws its circuit design directly from the Reference 80S, delivering the tonal density, bass control, and spatial expansiveness of Audio Research's Reference line in a more accessible package. Four KT150 output tubes in a fully balanced, differential signal path produce power that's honest and musical, with auto-bias keeping performance consistent as tubes age and line voltage fluctuates. Built entirely in Audio Research's Minnesota facility, the D-80 is tested twice and individually auditioned before it ships.

Key Features of the Audio Research D-80

• Reference 80S Foundation: Circuit topology derived directly from the Reference 80S stereo tube amplifier, bringing Reference-grade performance to a new price point.
• KT150 Output Tubes: A matched pair of KT150s per channel delivers 70 watts continuous with wide bandwidth and low distortion.
• Fully Balanced Differential Topology: The entire signal path is balanced and differential, maximizing noise rejection and delivering a fully balanced output to both speaker legs.
• Auto-Bias: Continuously monitors and adjusts output tube bias in real time, compensating for line voltage changes and tube aging with no user intervention.
• Full Pentode Design: Operates in pentode mode for maximum power and dynamic headroom from the KT150 output stage.
• 4, 8, and 16 Ohm Speaker Taps: Three output impedance taps allow proper matching to virtually any loudspeaker.
• Made in Minnesota: Entirely built, twice tested, and individually auditioned in Audio Research's U.S. facility.

Reference-Derived Circuit Architecture

The D-80 isn't just inspired by Audio Research's Reference amplifiers. It borrows directly from the Reference 80S platform. The fully balanced, differential signal path uses a pair of KT150 power tubes per channel, fed by 6H30 gain stage tubes. Internal components were chosen specifically to maximize tonal density, bass authority, and the reproduction of recording space. The result is an amplifier that sounds like it costs considerably more than it does, with the kind of weight and dimensionality that defines the Reference line.

Balanced-Only Input Design

The D-80 takes a purist approach with XLR-only balanced inputs. This keeps the signal path simple and optimized for the best possible performance. Most listeners pairing the D-80 with a quality preamplifier will have balanced outputs available, and keeping the circuit focused on one input topology means fewer compromises in the signal path. The output is fully balanced, driving both loudspeaker legs for maximum control and dynamic range.

Auto-Bias for Consistent Performance

Unlike amplifiers that require manual bias adjustment, the D-80's auto-bias system continuously monitors and adjusts the output tube operating point in real time. As tubes age or line voltage shifts throughout the day, the bias tracks automatically. The practical benefit is consistent sound quality every listening session without the need for a multimeter or periodic adjustments. When it's time for new tubes, simply install a matched set and the D-80 handles the rest.

Speaker Compatibility and Output Taps

Three sets of speaker output taps (4, 8, and 16 ohms) give you flexibility to match the D-80 to your loudspeakers properly. Correct impedance matching maximizes power transfer, controls damping, and ensures the amplifier operates within its optimal range. Output regulation is approximately 1.0dB from 16 ohm load to open circuit, yielding a damping factor of approximately 8, which is typical for a well-designed tube amplifier that balances control with the natural warmth of the output transformer.

Power and Bandwidth

The D-80 delivers 70 watts continuous from 20Hz to 20kHz with total harmonic distortion typically at 1% at 140 watts and below 0.04% at 1 watt. Power bandwidth extends from 7Hz to 68kHz at -3dB, while frequency response reaches from 0.7Hz to 94kHz at 1 watt. The slew rate of 10 volts per microsecond and 4.0 microsecond rise time give the D-80 the speed to handle transients cleanly, while overall negative feedback is kept at a moderate 15dB to preserve the tube character that makes Audio Research amplifiers special.

The D-80 Legacy

The "D" prefix carries weight in Audio Research's history. It traces back to legendary amplifiers that established the high-performance tube amplifier market. The D-80 is designed to carry forward the performance and gravitas of those ancestors while incorporating modern manufacturing and circuit refinements. It's not a nostalgia piece, it's a continuation of a design philosophy that has defined reference-quality tube amplification for decades.

Audio Research D-80 Stereo Power Amplifier Video

Explore the Audio Research Power Amplifier Range

Audio Research offers power amplifiers across a wide range of configurations and power levels. The Reference 80S delivers the full Reference circuit in stereo form. For more power, the Reference 160S offers 140 watts per channel. Those seeking monoblock performance can explore the Reference 160M MkII or the flagship Reference 330M. For listeners who want the simplicity of an integrated solution, the I/70 combines a tube preamp and 70-watt power amp in one chassis.

The Listening Room Difference

We're a third-generation family business with a brick-and-mortar showroom in Chestertown, Maryland, and a reputation built on trust, not hype. Whether you're visiting in person or ordering online, we bring decades of experience, personalized service, and honest guidance to every interaction. We don't just ship boxes. We help build systems, answer your questions like real humans, and make sure every detail of your setup is right, from the cables to the final connection. Our passion is helping you get the most out of your gear, with support that lasts well beyond the sale.

Audio Research D-80 Stereo Power Amplifier Specifications