The Xs Phono is an all-out assault on the state of the art in Vinyl, perhaps the most intensive and difficult design effort Pass Labs have made. Paradoxically from the company priding itself on simplicity, it appears to be very complex, having circuits which contain a total of about 1,500 components. However, this massiveness is used to extract the utmost performance from a simple topology operating with the extremely small and delicate signals coming from the wide variety of phono cartridges.
The job of a high-end phono stage is made more complicated by the requirements for high gain and accurate equalization. More difficult yet is
the incredible dynamic range that it must address – phono cartridges with rated outputs as low as 0.2 millivolts offer information at levels 10,000 times lower at about 0.00002 millivolts (20 nanovolts, or billionths of a volt). The Xs phono stage inputs achieve a noise floor about 35 dB below this figure using paralleled NOS Toshiba 2SK170 Jfets (all told each Xs Phono uses about 100 of these very expensive and hard-to-get parts).
It is not just a matter of input noise. Pass Labs experiments with switching signals at these levels demonstrated problems even with relays design to switch at microvolt levels. For this reason, Pass Labs have chosen to minimise switched connections by using three separate dedicated input systems.
When you are amplifying low frequency signals by about 100,000 times, long term connection quality and resistance to mechanical vibration become more important than ever, so they have not only gone to gold plated high temperature ceramic circuit boards, but suspended them on elastomeric mounts and mounted them in a heavy machined aluminum chassis.
All important to the performance, the power source for the Xs Phono is housed in a separate chassis, with an actively regulated and passively filtered supply system which draws a constant 75 watts.
It goes without saying that the distortion is very low and the RIAA equalisation is very accurate. While the measured performance of the Xs Phono reflects the quality of the parts and the high standards of assembly and testing, behind this is many man-years of experience with high-end phono amplification and years of prototyping and listening to all the elements that sum to the Xs Phono Stage.