The new XP-12 starts with a new power supply. It uses an efficient toroidal design with both an electrostatic and Mu metal shield along with vacuum impregnating and epoxy fill. This gives us a very quiet transformer both electrically and mechanically.
The power supply circuitry itself is also lower noise and has additional filtering, a little more complicated but worth it.
The XP-12 uses the single stage volume control borrowed from the XS line preamp. This gives us one hundred 1 dB steps with lower noise and distortion while removing some signal path parts.
The gain circuitry continues to use Pass Labs favourite transistors from Toshiba but has a larger higher biased output stage similar to the XS preamplifier auto bias. This makes longer and multiple cable runs easier to drive and gives the advantage of simplifying the single ended output circuitry while increasing performance. Overall this makes for a quieter more neutral, musical and versatile control center for your system.