Pass Labs XP-12 Preamplifier and XA25 Amplifier

The Wonderful World of Color

Equipment report
Solid-state power amplifiers,
Solid-state preamplifiers
Pass Laboratories XA25,
Pass Laboratories XP-12
Pass Labs XP-12 Preamplifier and XA25 Amplifier

Sometimes an audio review boils down to a single clarifying moment—an instant that crystallizes what you were hearing from the very beginning but were struggling to capture in words. I’d been listening to the Pass Labs XP-12 linestage preamp and XA25 amp for weeks. It was obvious they were very special, but special how? Finally the answer appeared in, of all places, a gelato store that I frequent. I was looking at the rainbow array of flavors—a bright cartoon cacophony of color. That’s when I understood what I was tasting, or rather, listening to with these Pass components—a rush of sonic color, a vast and dense palette of pigments, delicate shades and half-tones spanning a dynamic, dimensional soundspace.

The recording that first put me in this mindset was the tasteful series of duets between guitarist Pat Metheny and bassist Charlie Haden from the album Beyond the Missouri Sky [Verve]—a brilliant exchange filled with complex harmonic interactions and fine gradations of dynamic energy. But it could just as easily have been the angelic backup harmonies which seemed to loft above my loudspeakers during Jennifer Warnes’ “Joan of Arc” from Famous Blue Raincoat. Or when I played back the mono recording of The Beatles’ “Revolution.” Even the guitar distortion grew more specific and heavier with illuminated layers of noise, feedback, and grunge, rather than just a dirty uncorrelated wash of aggression. It was the same colorful lesson each time.

Ironically, these are not even Pass Labs’ grand cru products. Actually the Pass Labs XP-12 preamp and XA25 amp represent a level of affordability unique for Pass separates, with pricing normally reserved for the firm’s superb integrated amps. As in all things Pass, there were quality and sonic refinement in abundance. This wasn’t sleight-of-hand trickery; rather, it was the ability of a mature company knowing what to leave in and what to take out without compromising the signal. The familiar aluminum-plate exterior was still formidable but not imposing. Except for the large, though far from massive, heatsinks festooning the XA25, these separates are smaller, unadorned, yet instrument-grade in appearance and construction. (A phonostage, the XP-17 at $4300 is also available. Look for my review in a forthcoming issue.)

The XP-12 preamp eschews the dual-chassis, outboard power supply of its uptown siblings in favor of a compact single chassis—an ideal fit for a modestly sized den or listening room. Nonetheless, the preamp is the recipient of a new power supply incorporating an efficient toroidal design that sports a mu-metal shield with epoxy fill—keys to producing a quiet transformer both electrically and mechanically. The power supply circuitry itself is also lower noise and has added filtering. All functions are microprocessor-controlled and never come into contact with the input and output signals. The digital circuitry is powered by its own power supply and fully isolated from the analog supply. Turning to the back panel there are five inputs, two of which are balanced XLR, the remaining three unbalanced RCA. Input five does double-duty as a home-cinema pass-through activated by the pushbutton remote control.

The single-stage electronic volume control is borrowed from the Xs line preamp. Designed by Pass Labs maestro Wayne Colburn, it has a greater than 70dB range and is driven by a micro-controller “that reads the optical encoder serving as a front panel volume control.” It offers an accuracy that Pass considers unavailable on an ordinary volume control, is extremely low in noise and distortion, and uses fewer signal-path parts. These are not minor issues. The heart of a preamp is the transparency of its volume control. Poorly implemented it can degrade the soundstage, distort the stereo balance, and rob a performance of dynamic energy. The gain circuitry continues to use Pass Labs’ favorite transistors from Toshiba, but has a larger, higher-biased output stage. Pass notes that this makes “longer and multiple cable runs easier to drive and provides the advantage of simplifying our single-ended output circuitry while increasing performance.”

The XA25 amp is a solid-state, Class A design, single-ended throughout. Power output is rated at 25Wpc and 50Wpc into 8 ohms and 4 ohms respectively, so users will need to be a little more careful about speaker selection. The XA25 is touted as “the most affordable power amplifier in the Pass line,” and as Nelson Pass writes: “It takes advantage of lower power requirements to have simpler single-ended circuitry and fewer parts in the signal path.” This also allows elimination of degeneration, what Pass describes as “that other negative feedback,” in all stages. And lower voltages mean the ability to run gain devices more deeply into Class A at higher bias currents.

As my introduction implied, “affordable” doesn’t begin to describe what’s going on musically. The sonic character of the Pass duo conveys a warm, embracing personality uncommon in solid-state amplification but consistent with my previous encounters with Pass amps. There’s a level of harmonic bloom across the spectrum—most notable in the resonances and decays of strings and winds. It’s a musically juicier quality of such ripeness that it might make you reach for a napkin. As I listened to the interplay of YoYo Ma’s cello, Edgar Meyer’s acoustic bass, and the fiddle of Mark O’Connor, I could follow each note from the initial transient right down to the unhurried decay. The XP-12/XA25 brought to life the outlines, ambient aura, and resonant harmonics of each of these instruments.