While the designer's book on the XA25 long closed, ours just opened. From the tech descriptions it certainly seems that being this catalogue's most affordable isn't synonymous with least sophisticated or interesting. For contrast I had their XA30.8 and FirstWatt F7; and this from HomeTheaterReview's Terry London: "Wanted to share that I just got through submitting my writeup on the Pass Labs XA25. I believe that this might be the best amplifier Nelson and his crew have yet created/built. I own a pair of XA-60.8, a FirstWatt SIT 2 and have had in my system an XA30.8. The XA25 does color, tonality, spatial qualities, bass control and overall macrodynamics different and better for my taste than these other wonderful amplifiers. I still cannot believe that I'm not listening to a great tube SET were it not for how quiet, quick and dynamic the XA25 presents the music."

The last and only other amplifier I'd reviewed then which ran high-power transistors as solitary pairs was the €20K Reimyo KAP-777. It outputs 200/400wpc into 8/4Ω to bias class A/B and does not advertise sub 1Ω stability. Others championing single transistor pairs with high power are Gato's 250-watt TwinFet PWR-222 at £11'180; and Gamut's 220wpc D200i stereo amp at £9'300. Then there are the now discontinued 55-watt LinnenberG Allegro monos at €5'000. There's probably more but likely not many. Once we specify class A with a $5K tag, Slim Pickens isn't just the stage name of one Louis Burton Lindley Junior. Obviously FirstWatt have options. From them we simply expect less current delivery and low-impedance happiness. For complex bass-heavy music and more reactive loads, closer heavier XA25 competition should come from the massively paralleled XA.8 models. My question was how a different circuit approach and 700w/40A output devices would influence sonics. First, the obligatory peek…

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… under the hood to reveal this bird's eye view on 18 power supply caps, the front-end board above those, a toroidal power transformer and, against the heatsinks, the output devices covered by floating circuit boards.

A side view shows more of an output stage PCB…

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… followed by the front-end board and more. As to the long view and what these big Mosfets presage for Pass, "the XA25 confirms our in-house view that removing degeneration delivers some nice effects. The primary rationale for the big Ixys parts however (as opposed to smaller parallel Fets) was that they are simpler to implement. Big Mosfets or not, more powerful product will have to take a different approach and that is under development as well as other refinements." So the primary attraction is the avoidance of ballast resistors. The big Ixys parts simply play enabler. In a subsequent email Nelson let slip that "the SIT-3 was recently revised as a result of marathon listening sessions. Another circuit version emerged the winner. I expect a pilot run to surface beginning of March followed shortly by production." This reiterates how final voicing decisions come about at Pass Labs: through an experienced listening panel, not a solitary decider.