Source: Press Release, Last Accessed: 2016/03/11

Unison Research are expanding on their class-leading knowledge of valve-based Hi-Fi electronics to produce their first ever dedicated headphone amplifier solution. The SH is a single-ended, two-stage full-valve headphone amplifier designed to accommodate both traditional analogue sources and modern computer-based audio.
According to the press release, the SH began with the same basic aim as the coveted Simply Italy integrated amplifier; to produce a world-class sound from a specialized device using the best technology available. However, to suit the particular factors associated with headphone listening, the development team also had to ensure that the amplifier was designed with low noise characteristics and low internal impedance. The result was a fairly simple linear circuit with low negative feedback that produces an output voltage which is more than capable of driving a wide range of headphones, while keeping distortion low throughout the frequency range. Great care and attention was given to the layout and selection of components for the SH, the company says. To compensate for the low negative feedback required in the design, absolute attention was paid to ensure optimal linearity and increased attention on managing noise to a minimal level throughout the electrical path. It’s thanks to this design that the SH is able to deliver a consistent, coherent, rich and identifiable “valve” sound character when in use.
The input stage uses an ECC83 valve, while the output stage uses one EL84 (both valves operating in triode mode). According to Unison Research, the benefits to using this specific combination of valves are two-fold. First, the application requires reduced power compared to how the valves are usually employed, resulting in extended life. Second, the EL84 is capable of producing enough power to also drive the specially-selected output transformer with optimal electrical and sound character.
The SH has two headphone outputs that are connected in parallel (each with their own EL84 valve) for easy switching between headphones, or to accommodate multiple listeners. There is also a “Sensitivity” switch, to ensure the widest possible range of headphones can be comfortably driven by the amplifier. The added advantage of this switch is for maintaining premium sound quality while listening to music at lower volumes, as both sensitivity options will likely work with the vast majority of high-end headphones. The volume stage is entirely passive.
In addition to a standard unbalanced RCA input for connecting any Line-level source, the SH is also equipped with a class-leading USB DAC. The asynchronous USB 2.0 technology is the same as found on the recent Triode 25 amplifier, and supports audio formats up to 384kHz PCM and DSD 128. The patented jitter elimination circuit ensures a great sonic performance, assisted by the galvanic isolation employed between the power areas of the USB interface and the conversion IC. This additional input option brings SH up-to-date with the latest requirements of computer-based headphone audiophiles.
As with all Unison Research products, R&D and production for the SH took place in-house at the company’s Treviso-based facility. The stylish wood front-panel is locally sourced and finished to the highest quality, as with almost all other components.

For more information: http://www.unisonresearch.com/

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