Unison Research REFERENCE TUBE Mono Valve Amplifier at Vinyl Sound Buffalo, NY USA

The REFERENCE TUBE is a mono valve power amplifier from Unison Research (Treviso, Italy), available at Vinyl Sound in Buffalo, NY, USA. Reviewed by Stereophile in 2025, it is the flagship monoblock from Unison Research and represents the culmination of the company's decades-long expertise in 845 triode amplifier design. Operating in pure Class A with a double parallel single-ended output stage, the REFERENCE TUBE deploys four 845 output triodes per channel, produces output power across both 4-ohm and 8-ohm taps, and spans a frequency range of 20 Hz to 30 kHz. Each monoblock weighs 155 lbs (70.3 kg) and measures 19.3 x 30.5 x 11.2 inches, making it among the most physically commanding amplifiers in contemporary high-end audio.

The Summit of 845 Triode Engineering

The REFERENCE TUBE's output stage places four 845 directly-heated triodes -- among the most physically large and sonically celebrated vacuum tubes in audio history -- in a double parallel single-ended configuration per channel. Each 845 receives an independent DC heater supply, eliminating AC heater-induced noise at the signal level and contributing to the amplifier's measured unweighted signal/noise ratio of 72.4 dB (ref. 1W into 8 ohms), improving to 93.8 dB A-weighted. The driver stages use one ECC82 and one ECC83 tube per channel, providing voltage gain and the bias current required to operate the four 845s in linear, low-distortion Class A. A feedback factor of 14 dB maintains frequency response flatness across the audio band. The Stereophile review noted the output impedance of the REFERENCE TUBE measured just 0.3 ohms at both 20 Hz and 1 kHz -- an exceptionally low figure for a single-ended tubed output stage, resulting in a frequency response variation of only ±0.2 dB with a standard simulated loudspeaker load.

Construction, Materials, and Industrial Design

The REFERENCE TUBE's chassis combines a polished stainless steel base plate with cherry wood side panels, following Unison Research's longstanding commitment to the integration of fine wood and metal in its reference products. The wood panels are functional as well as aesthetic: Unison Research states that they contribute to resonance damping in the metal chassis, reducing microphonic interference at the output stage. The rear of each chassis slopes upward from the tube platform to house the power supply section, high-quality filter capacitors, and the custom output transformers wound in-house at the Unison Research facility in Treviso. Both RCA and XLR balanced inputs are provided, with input impedances of 47k ohms (RCA) and 10k ohms (XLR). Two output transformer taps -- 4 ohms and 8 ohms -- enable precise matching with a wide range of loudspeaker nominal impedances.

Key Features

• Four 845 Output Triodes per Channel: Double parallel single-ended Class A output stage using the iconic 845 directly-heated triode -- Unison Research's most powerful single-ended valve configuration.
• Pure Class A Operation: The entire output stage operates in pure Class A at all times, with no crossover distortion and full bias current maintained regardless of signal level.
• Independent DC Heater Supplies: Each 845 receives its own dedicated DC heater supply, eliminating AC hum at the output stage.
• Ultra-Low Output Impedance: Measured at 0.3 ohms at 20 Hz and 1 kHz, the REFERENCE TUBE presents an unusually low source impedance for a single-ended design, ensuring stable frequency response with real loudspeaker loads.
• Balanced and Unbalanced Inputs: Both XLR (10k ohm) and RCA (47k ohm) inputs allow connection to a wide range of preamplifiers, including the matching Unison Research REFERENCE PRE.
• Dual Output Taps: Separate 4-ohm and 8-ohm output transformer taps enable precise impedance matching with the connected loudspeaker.
• Cherry Wood and Polished Steel Chassis: Handcrafted in Treviso, Italy, with cherry wood side panels and stainless steel base, combining structural rigidity with resonance damping.
• Stereophile Reviewed 2025: The REFERENCE TUBE monoblock was evaluated in full by Stereophile magazine in 2025, with measurements confirming its specifications and a highly favourable listening assessment.

Technical Specifications

Awards and Critical Recognition

• Stereophile full review with measurements, 2025 -- described as the pinnacle of Unison Research's valve amplifier engineering, with measured output impedance of 0.3 ohms and an A-weighted signal/noise ratio of 93.8 dB.

Frequently Asked Questions

What is the Unison Research REFERENCE TUBE mono amplifier?

The Unison Research REFERENCE TUBE is a mono pure Class A valve power amplifier from Treviso, Italy, using four 845 output triodes in a double parallel single-ended configuration. It produces 80 watts into 8 ohms (per Stereophile measurements), spans 20 Hz to 30 kHz, and features both RCA and XLR inputs along with 4-ohm and 8-ohm output taps. It is the flagship power amplifier in the Unison Research range.

How does the REFERENCE TUBE compare to the Unison Research ABSOLUTE 845 integrated amplifier?

The REFERENCE TUBE monoblocks and the ABSOLUTE 845 both use 845 triodes in pure Class A single-ended configurations, but they differ fundamentally in form and power. The ABSOLUTE 845 is an integrated stereo amplifier producing 40 watts per channel using four 845 tubes in total across both channels. The REFERENCE TUBE is a dedicated monoblock power amplifier producing approximately 80 watts using four 845 tubes per channel alone, requiring a separate preamplifier such as the REFERENCE PRE. The REFERENCE TUBE is the higher-powered, fully separated solution for the most demanding system configurations.

What preamplifier pairs with the REFERENCE TUBE?

Unison Research designed the REFERENCE PRE tube preamplifier as the purpose-matched companion to the REFERENCE TUBE monoblocks. The REFERENCE PRE is a dual-mono, three-chassis tube preamplifier using 300B, ECC82, ECC83, and 6C45P tubes in pure Class A, with four line inputs (two balanced), two phono inputs, and a 500-ohm output impedance that matches the REFERENCE TUBE's 47k-ohm RCA and 10k-ohm XLR input impedances. The pair can be operated via Unison Research's remote switch-on system for simultaneous power-on from a single control point.

What is the 845 tube, and why does Unison Research favor it?

The 845 is a directly-heated triode transmitting tube originally developed for radio broadcasting applications. In audio amplification, its large physical size, directly heated cathode, and high plate voltage operation produce a harmonic structure dominated by low-order even harmonics -- principally the second harmonic -- which many listeners associate with a warm, tonally rich, and dimensionally open sound character. Unison Research has been a leading advocate for the 845 triode since it introduced the ABSOLUTE 845 in the early 1990s, which The Absolute Sound recognized as the best product of 1994.

Where can I buy the Unison Research REFERENCE TUBE monoblock in Buffalo, NY or the USA?

The Unison Research REFERENCE TUBE mono valve amplifier is available at Vinyl Sound in Buffalo, NY, USA. Vinyl Sound is an authorized Unison Research dealer serving western New York and the broader United States market. Contact Vinyl Sound for current availability, in-store audition arrangements, and expert advice on system configuration with the REFERENCE PRE preamplifier.