Pass Labs XA30.5 power amplifier Erick Lichte August 2009

Erick Lichte wrote about the Pass XA30.5 in August 2009 (Vol.32 No.8):

Have you ever dated a girl and then, six months into the relationship, met her superhot younger sister? That pretty much sums up my long-term romance with my old Pass Labs Aleph 3 power amplifier ($2300 when available but long discontinued), and my flirtatious liaison with the übersexy Pass Labs XA30.5 ($5500).

Knowing that I owned an Aleph 3, John Atkinson pimped out an XA30.5 to me so that I might compare the two. I jumped at the chance—I love my Aleph 3 (footnote 1) and wanted to see how Nelson Pass's design work had evolved into an amp of similar size and function.

The XA30.5 shares the genus of the Aleph 3's high bias into class-A, the use of MOSFETs, and its stated output of 30Wpc into 8 ohms. But beyond that, Nelson Pass's natural selection and evolution have turned the XA30.5 into a new species of amp. The XA30.5 uses Supersymmetry that allows the amp to go into push-pull mode for greater peak power, among other significant changes and innovations. And unlike my Aleph 3, it accepts balanced inputs.

Not only has the XA30.5 evolved on the inside, but this girl has had some work done on the outside. Sitting next to my cute but slightly dowdy Aleph 3, the XA30.5 looked all kinds of sexy. Voluptuous curves of thick faceplate, outstretched wings of heatsinks, and an enticingly glowing meter told me this girl cared about how she looked. It was like the difference between the two young female castaways on Gilligan's Island: the Aleph 3 is a pert Mary Ann, the XA30.5 a sultry Ginger. And speaking of TV, I couldn't help noticing that the Aleph 3's cubical resemblance to the Borg matched well the XA30.5's feel of the mothership Enterprise (the NCC-1701-D, of course).

The XA30.5 also shares with the Aleph that "lit from within" sonic quality that many people speak of when talking about single-ended, class-A amps. Some amps are all about control, which the XA30.5 has, but my overall impression was that this amp let the music flow instead of micromanaging every aspect of the sound. The music came out as an organic whole, with nothing lacking and nothing overemphasized. It made music out of everything I fed it without stumbling into the pitfall of an overly euphonic, laid-back, hazy sound.

I was blown away by how much unforced musical information the new Pass passed along while retaining a certain sweetness in its sound. The delineations between instruments and their surrounding spaces were easily discerned and musically compelling. Listening to Son Lux's densely mixed At War with Walls & Mazes (CD, Anticon ABR0082) was incredibly involving. Each instrument, sample, and electronic effect came to life with a patchworked, kaleidoscopic effect—the effect I think Son Lux (aka Ryan Lott) was after.

I'd bought my little Aleph 3 because it reproduced human voices better than any other solid-state amp I'd heard, so I thought I'd begin my head-to-head Pass comparisons with vocal music. I listened to the Latvian Radio Choir perform Eriks Esenvald's stunning composition Légende de la femme emmurée, from their Glorious Hill (CD, GB Records CD09). The work is a subtle tour de force: First a small choir, toward the rear of the soundstage, sings a setting of Albanian folk-song texts full of turns and trills. They're then joined by a large choir in the middle of the stage, and finally by two sopranos in the foreground, singing a heartbreaking duet in English. My Aleph 3 worked its usual magic: Voices were full-bodied and rich, with the sort of resolution and texture in the midbass I normally hear only from higher-bit-rate recordings and/or single-ended tube amps. When I switched to the XA30.5, the voices lost some of the midbass body I'd heard through the Aleph. Sibilants seemed a bit more present through the XA30.5, but had less grain than through the Aleph. The XA30.5 did a better job—or, shall I say, a more distinct job—of the back-to-front layering of the big choir and the foreground sopranos. Though there were differences in sound between the two amps, they were subtle; a few minutes into the switch, I'd forgotten about them and was just enjoying the music.

Next, I turned to some music of a less subtle nature. Last January I got to hear John Atkinson play "Love Lockdown," from Kanye West's 808's & Heartbreak (CD, Roc-A-Fella B0012442-02), on his system, which at that time included the Musical Fidelity 750k Superchargers and the Revel Salon2 loudspeakers. It was loud and it was awesome. When I listened to this track at my house, my Aleph 3 couldn't even come close to what I'd heard at John's; it just couldn't play loud enough to make that song do what it's supposed to. It was with some hope, then, that I tried this track with the XA30.5 driving my Revel F30s.

The new Pass amp could certainly play louder, and its presentation was closer to what I'd heard at JA's house, but it still couldn't quite stick balls to walls. I found that the XA30.5 gave satisfying renderings of symphonic works containing large but short-term dynamic swings, but neither Pass really fit the bill for the constant pounding of electronic music played at high volume. These are, after all, nominally 30Wpc amps. I conjecture that the bigger amps in Pass Labs' Aleph and XA.5 series may be able to overcome this limitation.

Initially, I did all of these comparisons using the XA30.5's single-ended input. Switching to its balanced inputs allowed the XA30.5's performance to pull further away from the Aleph 3's. Listening to the Fleet Foxes' eponymous album (CD, Sub Pop SPCD 777) through the balanced connections resulted in a wider soundstage, greater resolution, and even less grain. The sound of the band's mountain-music-meets-Beach-Boys "White Winter Hymnal" was both more solid in the stereo space and resolved more of the decay from whatever reverb-drenched space they created. The balanced inputs seemed to pass more musical information than the single-ended. The XA30.5's slightly leaner midbass presentation and more forward midrange and treble persisted. But again, this was never a problem—many recordings benefited from the slight tonal shift, giving the music a bit more excitement and clarity.

Resistance to loving the sound of either of these amps was futile, yet there were differences. The Aleph 3's lush midrange and full midbass are paired with a less-airy treble. It's dynamically limited, especially if you feel the need to rock out hard. The more-resolving XA30.5 can punch even higher above its 30Wpc weight class than can the Aleph 3, with a bit better bass control but with a leaner midbass and a slightly more present top three octaves. And using the XA30.5 in balanced mode improved the amp's already great performance.

It was a pleasure and a challenge to compare and contrast these two wonderful solid-state amplifiers from Pass Labs. Though still in love with my Aleph 3, I really enjoyed flirting with the XA30.5.—Erick Lichte

Footnote 1: Muse Kastanovich reviewed the Aleph 3 in April 1997, Vol.20 No.4.
Pass Laboratories
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Foresthill, CA 95631
(530) 367-3690