Audio Research LS2B
At 6.0kg and just 134mm tall, it sits in a rack like a quiet declaration—solid, serious, and built for balance.
Overview
The Audio Research LS2B is a line stage preamplifier from the early 1990s, designed without phono input and built around a fully balanced hybrid architecture. Marketed under variations of the name—LS2B MKII, LS2B Mark II, or LS2B MkII Stereo Tube Hybrid Preamplifier—it occupies a niche in Audio Research’s history as a transitional design that merged solid-state reliability with the warmth of tubes. The unit uses a single twin-triode 6DJ8 tube at its signal path core, while the rest of the circuit, including the power supply, relies on FET-based solid-state components. This hybrid approach was intended to deliver the speed and control of transistors with the harmonic richness typically associated with all-tube designs.
Owners report a clean, open sound with strong spatial imaging, particularly when paired with high-current tube amplifiers. It was offered with an optional remote control, which added $500 to its $2,995 MSRP at launch. The preamp features five high-level inputs, though some sources list six line inputs and one tape loop system, suggesting minor revisions or configuration differences across units. Balanced XLR inputs are standard, emphasizing its fully balanced signal path—a rarity in preamps of its era at this price point. Despite its hybrid nature, it is not a power amplifier; a single Facebook post erroneously listing 50 watts per channel is likely conflating the LS2B with a power amp model and is disregarded.
Specifications
| Manufacturer | Audio Research |
| Product type | Preamplifier / Control Amplifier |
| External dimensions | Width 480 x Height 134 x Depth 260 mm |
| Weight | 6.0kg |
| Input terminal | Line : 6, Tape : 1 system |
| Output terminal | Unbalanced : 20V/250 Ω, Balanced : 500 Ω |
| Frequency characteristic | 1 Hz to 100 kHz ± 0.5 dB |
| Power consumption | 60W |
| Controls | Gain, Power |
| Balanced input impedance | 3M ohms |
Key Features
Fully Balanced Hybrid Tube and Solid State Design
The LS2B is built around a balanced hybrid topology, a deliberate engineering choice to combine the best attributes of both solid-state and tube technologies. Most of the signal path, including regulation in the power supply, uses FETs as the primary active components, ensuring low noise and high current stability. The single 6DJ8 twin triode tube is used selectively within the gain stage, contributing subtle harmonic saturation without compromising control. This configuration avoids the microphonics and drift common in all-tube preamps while preserving tonal richness.
Line-Only Control Amplifier with Balanced XLR Inputs
Designed strictly as a line-level preamplifier, the LS2B omits phono circuitry entirely, focusing instead on optimizing high-level signal handling. Its six line inputs include balanced XLR connectors, allowing users to take full advantage of the internal balanced circuitry when paired with compatible sources. The high 3M ohm input impedance ensures minimal loading on upstream devices, preserving transient detail and dynamics.
Low-Noise Tube Implementation with FET Support
The 6DJ8 tube is specified as a "QUALITY LOW-NOISE TUBE," selected for its reliability and quiet operation. Positioned at the heart of the gain stage, it operates within a carefully regulated environment supported by solid-state FET circuitry. This hybrid topology reduces the need for excessive global feedback, contributing to a more natural, dynamic presentation. However, some users have reported audible hiss, particularly in high-gain systems, indicating that tube matching and circuit aging may influence noise performance over time.
Collectibility & Value
The LS2B was produced in 1992, placing units well over 30 years old today. In 2013, Audio Research Lab listed a quotation range of 1,000 to 1,200 EUR for units in working condition. One example arrived for service in good working order and received only a light service, suggesting inherent reliability when maintained. A unit refurbished by Audio Research in early 2024 indicates that factory support, at least for servicing, may still exist or have been available recently. Despite its age, user feedback on forums gives it a 4.9 out of 5 rating, reflecting strong satisfaction among owners. The primary user complaint centers on excessive gain when paired with sensitive power amplifiers, underscoring its high output capability. No data is available on spare parts availability or common failure modes beyond occasional hiss.
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