The Audio Research D-80 is a 70-watt-per-channel stereo tube power amplifier built around the same basic platform as the Reference 80S. It uses a fully balanced, differential signal path and a pair of KT150 output tubes per channel, with the output stage operating in pentode mode.
 
The D-80 is part of Audio Research's long-running D-series amplifier lineage, but its design is closely related to the company's current Reference amplifiers. Audio Research developed the D-80 as a more straightforward alternative to the Reference 80S, retaining its core circuit architecture while omitting features such as triode/pentode switching and the Reference model's glass front-panel display.
Each channel uses two matched KT150 output tubes, while two 6H30 tubes provide the gain stage. The amplifier is fully balanced from input through output, with both legs of the speaker load actively driven. Audio Research uses a relatively simple signal path and 15dB of overall negative feedback.
 
One of the most useful features is the D-80's automatic bias system. Rather than requiring the user to manually check and adjust the output tube bias, the amplifier continuously monitors and adjusts the bias of the KT150 tubes. It compensates for changes in line voltage and tube age, helping maintain consistent operating conditions as the tubes are used over time.
 
The D-80 has only balanced XLR inputs. Audio Research designed it with the expectation that it would be partnered with a balanced preamplifier, and the fully balanced architecture is carried through to the speaker outputs. Three sets of speaker taps are provided for 4, 8 and 16 ohm loads, allowing the amplifier to be matched to a wide range of loudspeakers.
 
Rated output is 70 watts continuously from 20Hz to 20kHz. The amplifier has a power bandwidth of 7Hz to 68kHz at -3dB and a frequency response of 0.7Hz to 94kHz at 1 watt. Audio Research specifies a damping factor of approximately 8 and 15dB of overall negative feedback.
 
The D-80 also includes a 12V remote trigger for integration with a compatible preamplifier or control system. Like other current Audio Research amplifiers, it is built, tested and individually auditioned at the company's Minnesota facility.
 
Key Features
• Stereo tube power amplifier
• 70W per channel continuous output
• Fully balanced, differential circuit design
• Pentode operation
• 2 × KT150 output tubes per channel
• 2 × 6H30 gain-stage tubes
• Automatic real-time output tube bias
• Balanced XLR inputs
• Fully balanced output stage
• 4, 8 and 16 ohm speaker taps
• 15dB overall negative feedback
• Approximately 8 damping factor
• 12V remote trigger
• Hand-built in Minnesota
• Based on the Audio Research Reference 80S platform