New Headphone Amplifier from Unison Research

Posted on 18th September, 2015

New Headphone Amplifier from Unison Research

Italy has a vast array of audio manufacturers, some even considered household names. Unison Research is one such boutique manufacturer, and their new SH headphone amplifier is the result of nearly 30 years in the business.

Unison Research SH Headphone Amplifier

The Unison Research SH is a class A, single-ended headphone amplifier with internal USB DAC. It is made with a tube circuit with only two stages (both operating in triode mode) and preceded by a passive volume control. Keeping circuitry simple contributes to a linear and modest frequency extension. The output stages of the SH use pentodes (the well-known EL84) used in triode mode.

An EL84 can operate in single-ended amplifiers to produce up to 4.3 watts, and Unison Research says:

The result is distortion typically below 0.15%, despite the feedback output / input (which does not include the output transformer) that is equal to just 16 dB.

This “residue” of distortion is also formed only by the second harmonic and (in smaller quantities) from the third harmonic to about 0.6V (headphone output to low sensitivity, 33 ohm load) and is completely constant with frequency. This determines an absolutely coherent tonal quality while listening; all the components of the music program are delivered with the same “character” of sound.

Unison Research SH Headphone AmplifierWith just two inputs (Unbalanced RCA, USB) and two outputs connected in parallel, the SH has a switch to adjust the amplification based on the type of headphones used; high sensitivity and low impedance (16 to 40 ohms, on average about 30 ohms), and low sensitivity and high impedance (typical values between 60 and 150 ohms).

The SH also features an internal USB DAC. It uses the latest generation ESS Sabre conversion DAC, with the patented jitter elimination circuit, accepts PCM up to 384kHz and DSD up to 128x, and up to 32bit resolution.

Unison Research SH Headphone Amplifier


  • Max output power (THD 1%):
    Output “High sensitivity” 0.5 V on 150 ohm, 0.45 V on 33 ohm, 0.4 V on 10 ohm
    Output “Low sensitvity” 1.4 V on 150 ohm, 1.1 V on 33 ohm, 0.6 V on 10 ohm
  • Frequency response : -0.1 dB @ 10Hz / 3-dB @ 50 kHz
  • Input impedance : 20 kohm // 100 pF sensitvity 0.67 V:
    High sensitvity, ( 10 ohm load ) 0.33 V out
    Low sensitvity, (33 ohm load ) 1 V out
  • Input stage: Pure Class A, ECC83/12AX7
  • Output stage : Class A, EL84 triode mode
  • Input: 1 RCA line, 1 USB
  • Output: 2 in parallel
  • Feedback: 16 dB
  • Output impedance: 6.9 ohm
  • THD: < 0.2% @ 1kHz, 0.5V, <0.8% to 1 V (out “Low sens.” on 33 ohm)
  • Power consumption: 45 W
  • Dimensions: 22.5 cm x 12.6 cm x 32.2 cm
  • Weight: 6 kg

Unison Research SH Headphone Amplifier with USB DAC is available now for $2,650 RRP.

Unison Research is distributed in Australia by Radiance Audio Visual.

Marc Rushton's avatar

Marc Rushton

StereoNET’s Founder & Publisher and still buried deep in the review room auditioning everything from docks to soundbars, amplifiers and headphones. Marc is also the founder of the annual International HiFi Show.

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Posted in: Headphones
Tags: radiance audio visual  unison research  headphone amplifier