Audio Research I/70 Integrated Amplifier

70 Watts Per Channel of KT120 Tube Power With Auto-Bias, Flexible Preamplifier Outputs, and Optional Phono and Digital Modules

The Audio Research I/70 brings the company's tube preamplifier and power-amplifier expertise together in a single integrated amplifier. Four KT120 output tubes deliver 70 watts per channel, while an output transformer derived from the Reference 75 amplifier connects the I/70 directly to Audio Research's established separates heritage.

The I/70 is designed and built by hand at Audio Research's Minnesota facility, where each amplifier is twice tested and individually auditioned in the company's reference system. Its industrial design takes cues from the REF330M, with anodized top and bottom plinths, a fully enclosed transformer array, machined aluminum, meshwork, and distinctive Audio Research badging.

Tube Power Without Manual Biasing

Auto-bias eliminates the routine adjustment traditionally associated with many tube power amplifiers. The I/70 continuously maintains the operating bias of its four KT120 output tubes, making tube ownership considerably more straightforward while maintaining proper operating conditions.

The amplifier provides dedicated 4-ohm and 8-ohm output taps for matching a range of loudspeakers. Audio Research rates the I/70 at 70 watts per channel continuously from 20 Hz–20 kHz.

Independent Preamplifier and Power-Amplifier Sections

The I/70 incorporates independent tube preamplifier and tube power-amplifier sections. Stereo preamplifier outputs provide additional system flexibility, including the ability to feed powered subwoofers equipped with line-level inputs.

An active tube preamplifier section and 75-step volume control provide a broad range of level adjustment, particularly useful when moving among sources and recordings with substantially different output levels.

Optional Phono and Digital Capability

The standard analog input complement consists of three sets of single-ended inputs and one balanced XLR input. Optional phono and digital boards expand the I/70's source capabilities.

The optional phonostage accommodates both moving-magnet and moving-coil cartridges, with gain settings selectable from the I/70 remote. Moving-coil loading is adjustable from 50–1,000 ohms.

The optional digital board uses an AKM Velvet Sound DAC and provides USB, optical, coaxial, and Bluetooth connectivity. Incoming digital signals are upsampled by the DAC section.

Headphone Listening From the Main Output Tubes

Rather than relying on a separate convenience headphone circuit, the I/70's headphone output is driven by its KT120 output tubes. This gives headphone listeners access to the amplifier's primary tube output stage for personal listening.

Features

• 70 Wpc continuous tube output from 20 Hz–20 kHz
• Four KT120 output tubes with automatic biasing
• Output transformers derived from the Audio Research Reference 75 amplifier
• Independent tube preamplifier and tube power-amplifier sections
• 75-step volume control
• Three single-ended analog inputs and one balanced XLR analog input as standard
• Stereo preamplifier outputs for external amplification or powered subwoofers with line-level inputs
• 4-ohm and 8-ohm speaker output taps
• Headphone output driven by the KT120 output tubes
• Optional MM/MC phonostage with remotely selectable gain and adjustable MC loading from 50–1,000 ohms
• Optional AKM-based digital board with USB, optical, coaxial, and Bluetooth inputs
• Eight total inputs with both optional phono and digital boards installed
• Available with black or silver anodized plinths
• Hand-built, twice tested, and individually auditioned at Audio Research's Minnesota facility

Specifications

Power Output: 70 Wpc continuous from 20 Hz–20 kHz; 1 kHz total harmonic distortion typically 1% per channel, below 0.1% at 1 W

Power Bandwidth (-3 dB Points): 10 Hz–22 kHz

Frequency Response (-3 dB Points At 1 W): 7 Hz–30 kHz

Input Sensitivity: 1.25 V RMS for rated output

Input Impedance: 100 kohms balanced; 48 kohms single-ended

Output Polarity: Non-inverting; balanced input pin 2+ (IEC-268)

Standard Analog Inputs: Three single-ended, one balanced

Maximum Inputs With Optional Phono And Digital Boards: 8

Output Taps: 8 ohms, 4 ohms

Power Requirements (US): 105–130 V AC, 60 Hz; 420 W at rated output, 220 W at idle

Tubes Required: Two matched pairs KT120; three 6922 (one input, two driver)

Dimensions (H × W × D): 8.25" x 16.5" x 13.5" (210 x 420 x 340 mm)

Weight: 55 lb. (25 kg)