Unison Research – Phono One – Class A Valve Phono Preamplifier

Unison Research – Phono One – Class A Valve Phono Preamplifier

PhonoOne has been one of the most appreciated UnisonResearch units. Even though the production of this item was discontinued some years ago the requests never stopped, so it was decided to renew and improve this design. Nothing was changed in the external design as the original was so beautiful and timeless. Even after many years it has untouched aesthetic appeal.

The circuit implemented has lots of features in common with the SimplyPhono, here one more tube has been used, bringing up to 10 the number of triodes (i.e. 5 ECC83/12AX7 double triodes). All of the gain stages are now implementing parallel configuration for the best noise and distortion performances. This solution increases also the overall gain to approximately 54dB, enough for all the MM and most of the MC cartridges. The same passive RIAA network has been adopted but with special selected components in order to ensure strict tolerance to the equalization curve. Increased value for the output capacitors improves bandwidth and phase rotation at low frequencies.

In order to avoid the problem of DC voltage and bump during the warm up and switch off time of the unit, a delayed muting function has been implemented. This way the output is disabled until the tubes reach their optimal temperature and working point at the switch on and also prevent the loud bump at the switch off. While in SimplyPhono only the resistive component of input impedance is selectable, here both resistance and capacitance can be matched to the requirement of any cartridge for best performance. A dedicated free location on the PCB allows the installation of custom value resistors in order to set the interface parameters even at any non common value.

Particular care has also been dedicated to power supply design. In order to minimize cross-talk and inter-stage interference an independent RC filter cell has been placed near every gain stage, thus reducing the cross-talk (especially at low frequency) of more than 20dB in comparison with the extraordinary performances of SimplyPhono. In the new PhonoOne low frequency cross-talk is practically immeasurable, less than -90dB. Also a careful layout design improving channel separation and interference rejection, together with an elastic suspension of the amplifier board helped bringing the sonic performances of the new PhonoOne to a supreme level of natural detail and musical clarity.

As imposed for a no-compromise design, all the supply voltage are regulated and heavy filtered. Nothing has been neglected: all the signal wiring are hand soldered using shielded wire, the placement of the tubes takes care of the mechanical micro distortion of the physical parts of the tubes when operated in horizontal position, oversized power components and adequate cooling ensures high reliability.

Unison Research is sure the new PhonoOne will be highly appreciated by anyone looking for a phono preamplifier able to offer an involving listening experience.