Unison Research are expanding on their valve-based hifi electronics to produce their first ever dedicated headphone amplifier. The SH is a single-ended, two-stage full-valve headphone amplifier designed to accommodate both traditional analogue sources and modern computer-based audio.

Unison Research have created SH in order to cater for the growing world of headphone audiophiles. As most readers will be well aware, headphones have become increasingly important in the high-end home listening environment and the SH was developed to offer a high-end valve alternative to the many solid-state headphone amplifiers that are currently available.

The SH began with the same basic aim as the company’s Simply Italy integrated amplifier; to produce a world-class sound from a specialised 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 capable of driving a wide range of headphones, while keeping distortion low throughout the frequency range. To compensate for the low negative feedback required in the design, 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 identifiably “valve” sound character when in use” says the recent press release from Henley Designs, the UK Distributor.

The input stage uses an ECC83 valve, while the output stage uses one EL84 (both valves operating in triode mode). The benefits to using this specific combination of valves are said to be 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. When set to “High Sensitivity”, the output voltage from the amplifier is reduced, and at “Low Sensitivity” it is at its maximum. The volume stage is entirely passive.

In addition to a standard un-balanced RCA input for connecting any Line-level source, the SH is also equipped with a 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. There’s a patented jitter-elimination circuit and galvanic isolation employed between the power areas of the USB interface and the conversion IC.

SRP £1,250.00