Audio Research I/55 Integrated Amplifier

The Audio Research I/55 is the successor to the I/50, keeping the same compact chassis and 50-watt power output while importing key upgrades from the I/70: auto-bias, an active tube preamplifier section with wider gain range, preamp outputs, and a tube-driven headphone amplifier. Four 6550WE output tubes with three 6922 signal tubes deliver the traditional Audio Research combination of power and grace, with the kind of bass depth and dynamic expression that makes this integrated amplifier punch well above its size. Available in six finishes with optional AKM DAC and phono cards.

Key Features of the Audio Research I/55

• 50 Watts Per Channel: Four 6550WE output tubes deliver 50 watts continuous from 20Hz to 20kHz with the dynamic headroom to drive a wide range of speakers.
• Auto-Bias (New Over I/50): Automatic bias adjustment keeps output tubes at optimal operating points without user intervention, a significant upgrade over the I/50's manual bias.
• Active Tube Preamplifier: Independent preamp section with a wider gain range than the I/50's passive preamp, improving performance with low-output sources and dynamically complex recordings.
• Preamp Outputs: Stereo preamplifier outputs for powered subwoofers or an external power amplifier as your system grows.
• Headphone Output via Output Tubes: The headphone amplifier is driven by the 6550WE output tubes for a genuine tube headphone experience.
• LexieTubes Display: Two LexieTubes provide input selection and volume information with the distinctive glow that defines the I/50 and I/55 aesthetic.
• Optional AKM DAC Card: Velvet Sound DAC chip with USB, Optical, Coax, and Bluetooth inputs, all upsampled.
• Optional Phono Card: MM and MC phono stage with adjustable MC loading (50 to 1,000 ohms) via remote.
• Six Color Options: Available in Black, Silver, Red, Blue, Gold, and White anodized finishes.

What's New Over the I/50

The I/55 isn't a cosmetic refresh. The most significant upgrade is auto-bias, which continuously monitors and adjusts output tube bias in real time. The I/50 required periodic manual bias checks, and the I/55 eliminates that entirely. The preamplifier section has been redesigned from a passive to an active configuration, providing a much wider gain range. This means better performance with source components that have lower output levels and improved dynamics with recordings that have wide dynamic range. Despite identical power ratings, the I/55 will deliver additional effective output due to the higher gain and headroom in its preamplifier section.

All-Tube Amplification

The I/55's amplifier section uses two matched sets of 6550WE power tubes fed by three 6922 input and driver tubes. This combination has been an Audio Research staple for decades, delivering the musical warmth, harmonic richness, and three-dimensional imaging that tube amplification is prized for. The independent tube preamplifier and tube amplifier sections give the I/55 the flexibility of separates in a single chassis, with the preamp outputs providing a path for system expansion.

Headphone Amplifier

Like the I/70, the I/55's headphone output is driven by the 6550WE output tubes rather than a separate solid-state circuit. This delivers the full character of the tube amplifier stage to your headphones, with the same tonal richness, dynamic range, and spatial presentation you hear through speakers. It's designed for high-quality headphones and delivers a personal listening experience that stands on its own.

Connectivity and Optional Cards

The I/55 provides three sets of single-ended (RCA) inputs and one set of balanced (XLR) inputs for analog sources. The optional DAC card adds USB, Optical, Coax, and Bluetooth digital inputs through an AKM Velvet Sound chip with upsampling. The optional phono card provides both MM and MC capability with MC loading adjustable from 50 to 1,000 ohms via the remote control. Use the Version selector to choose your configuration: I/55 Only, or add DAC, Phono, or both cards.

LexieTubes Display

Two LexieTubes provide display information for input selection and volume level, maintaining the distinctive visual character that made the I/50 instantly recognizable. The warm glow of the display tubes, combined with the light from the output tubes visible through the chassis, gives the I/55 a presence that no LED display can match. It's a design detail that connects you to the music before you've heard a note.

Six Color Options

The I/55 is available in Black, Silver, Red, Blue, Gold, and White anodized finishes. This is the same color palette that made the I/50 popular with listeners who want their electronics to complement their living space, not just sit in a rack. Each finish is applied to the same high-quality aluminum chassis, and all colors are available across all configurations.

Explore the Audio Research Integrated Amplifier Range

For more power and the Reference 75SE output transformers, the I/70 delivers 70 watts with the same modular card architecture in a REF330M-inspired chassis. The original I/50 remains available as the entry point to Audio Research tube integrated amplification. For those building a separates system, the LS-3 preamplifier pairs naturally with the D-80 or S-100 power amplifiers.

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 I/55 Integrated Amplifier Specifications