I/55 Integrated Amplifier By Audio Research

The I/55 integrated amplifier builds upon the acclaimed foundation of earlier models while incorporating many of the advanced features introduced in the higher-tier I/70. Designed for listeners seeking authentic tube sound in a compact and elegant component, it combines refined styling with impressive musical performance.

At its core is a fully tube-based amplification design featuring two matched pairs of 6550 output tubes driven by 6922 input tubes. This configuration delivers the rich tonal character, dynamic expression, and effortless musicality that tube audio enthusiasts value. Despite its compact footprint, the I/55 produces powerful bass response, expansive sound staging, and exceptional control across a wide range of loudspeakers.

Visually, the amplifier retains the sophisticated appearance of its predecessor while adding modern touches, including dual LexieTubes® displays for volume and input information.

One of the most significant upgrades is the inclusion of automatic biasing, which continuously maintains optimal tube performance without the need for manual adjustment. This helps ensure consistent sound quality and long-term reliability.

The I/55 features independent tube preamplifier and power amplifier sections, along with stereo preamplifier outputs for added flexibility, including easy integration with powered subwoofers or external amplification systems.

Compared to earlier designs, the active preamplifier section provides a wider gain range and increased headroom, improving dynamics and performance with low-level recordings while preserving clarity and detail at all listening levels.

For personal listening, the dedicated headphone output is powered directly by the 6550 output tubes, offering a premium headphone experience with the same warmth and musical engagement heard through speakers.

Digital playback capabilities are equally impressive thanks to a high-resolution DAC supporting USB, Optical, Coaxial, and Bluetooth connectivity. Advanced upsampling enhances transparency, detail retrieval, and tonal accuracy for high-quality digital audio reproduction.

Connectivity includes three single-ended inputs and one balanced XLR input. An optional phono stage supports both moving magnet and moving coil cartridges, with adjustable gain and loading settings conveniently accessible via remote control.

Blending classic tube performance with modern functionality, the I/55 delivers a versatile, high-end listening experience in a beautifully compact integrated amplifier.

• Power Output:
  • 50 watts continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 1% per channel, below 0.1% at 1 watt. (Note that actual power output is dependent upon both line voltage and “conditioning” i.e.: if power line has high distortion, maximum power will be affected adversely, although from a listening standpoint this is not critical.)
• Power Bandwidth: (-3dB points) 10Hz to 22kHz
• Frequency Response: (-3dB points at 1 watt) 7Hz to 30kHz
• Input Sensitivity: 1.25V RMS for rated output
• Input Impedance: 100K ohms Balanced, 48K ohms Single Ended
• Output Polarity: Non-inverting. Balanced input pin 2+ (IEC-268)
• Inputs:
  • 100K ohms Balanced, 50K ohms SE
  • 8 Inputs – 4 balanced, 4 single-ended
• Output Taps: 8 ohms, 4 ohms
• Power Requirements:
  • 105-130VAC 60Hz (210-250VAC 50Hz)
  • 252 watts at rated output
• Tube Required: 2 matched pairs 6550WE; 3 x 6922 (1 input, 2 driver)
• Dimensions:
  • Width 16.5” (42 cm)
  • Height 7.25” (18 cm)
  • Depth 13.5” (34 cm)
  • Weight: 40 lbs (18.1 kg); 51 lbs (23.1 kg) shipping weight