Boulder 500AE power amplifier Steven Stone, November 1997

Steven Stone compared the 500AE with the Pass Aleph 1.2 in November 1997 (Vol.20 No.11):

I spent several days comparing the Pass Labs Aleph 1.2 to my reference amplifier—the $9900/pair Boulder 500AE monoblock, using my Dunlavy Signature SC-VI loudspeakers. Both models share the ability to produce copious amounts of volume without stress, but each excels in dramatically different sonic parameters. My DATs of the Young Philharmonic Orchestra of Munich performing in Boulder's Chatauqua Auditorium, which I had recorded with J. Gordon Holt, had superior three-dimensionality through the Alephs. Car-engine noise outside the hall sounded much farther away (the Chatauqua is a shed rather than an enclosed auditorium, so noise from "outside" is far more noticeable than on a commercial release). However, through the Boulder 500AEs these low-level low-frequency noises had more detail and more specificity.

While the orchestra sounded harmonically more natural with the Pass amps, with the Boulders I was able to pick out individual parts more rapidly. Also, the Boulders more readily revealed problems in intonation and ensemble. The Pass amps were seductive; instead of being bothered by these little mistakes, I found myself wrapped up in the fabric of the music. If I listened carefully I could hear the same mistakes that were so obvious through the Boulders, but it's far easier to overlook the blemishes on a few trees when a redwood forest looks so magnificent.

While both amps produced images of similar size, the Alephs did a superior job of fleshing out the three-dimensional quality of musical instruments. Instead of the pinpoint lateral specificity of the 500AEs, the Pass amps produced a slightly more diffuse but multidimensional instrument location. On a recent JGH/SS recording of Engelbert Humperdinck's Hänsel und Gretel, singers move around the stage as they sing. The Pass captured the way their voices bounce off the floor and sidewalls with a bit more spatial accuracy than the Boulders. As the singers move, they often turn their heads away from the single stereo M/S pair of microphones flown over the front of the stage. The Pass amps' spatial acuity made it possible to tell which way the singers' heads were turned. Through the Boulders it was harder to make such a determination.

On dense pop mixes like "Orphan Girl," from Gillian Welch's Revival CD, produced by T-Bone Burnett (Almo Sounds AMSD-80006), the Boulder amps did a superior job of differentiating each instrument's specific part; the Alephs delineated the various dimensional layers of the mix with better specificity. "Orphan Girl" is a paradoxical recording: At first it seems to be a simple two-voices-and-two-guitars acoustic recording. Actually, it's a dense arrangement with six-string bass, electric guitars, and multiple Optigan tracks. The Aleph had the ability to locate each instrument with greater three-dimensional precision, while the Boulder individualized each instrument's particular lines with greater acuity.

This is akin to the difference between tube and solid-state electronics: Tubes often do better at re-creating three-dimensional space, while solid-state amps excel at rendering inner details. The Pass 1.2 was a very "tubey" amp in the way it handled dimensionality—it got the spaces right. While it was easier to pull a mix apart through the Boulder amp, through the Pass I could sit back and luxuriate in its dimensional complexity.

There were noticeable differences between these two amps at the frequency extremes. The Pass Aleph had a slightly softer, sweeter top end than the Boulder amp. On some recordings the 500AE seemed to have more top-end air, while on other recordings the 1.2 had greater delicacy. On my own recordings I preferred the Boulder's more extended high-frequency rendition, but on most pop and commercial recordings the Pass's slightly mellifluous, more reticent top end was very welcome. Again, the differences between archetypal solid-state and tube-amp sounds come to mind. If you're a "tube person," you'll feel right at home with the Pass 1.2's top-end rendition.

Bass through the Pass had exemplary pitch definition and "tunefulness," but lacked the dynamic drive of the Boulder amp. On Rickie Lee Jones's "Beat Angels" (Traffic from Paradise, Geffen GEFD-24602), John Leftwich's acoustic bass lines were more melodious with the Pass, but the Boulder amps transmitted more energy and dynamic life. If forced to choose which rendition was more accurate, I'd say "Both." Ideally, bass rendition should be melodious and dynamic, but these two amps demonstrate that perfection is still a goal, not a reality.

The Pass Aleph 1.2 is more dynamically relaxed than the Boulder. The horn attacks on Paquito D'Rivera's Portraits of Cuba (Chesky JD145) were just that—aggressive, with more dynamic energy through the 500AE amps. Through the Alephs, everything was just a bit softer, with less edge and dynamic punch. Dynamic peaks also seemed louder through the Boulders, with superior punch. While the Aleph lacked a bit of dynamic contrast, there was a natural-sounding harmonic envelope to the horn sound, especially the decay. Once more, the absence of any sort of electronic edge to the Pass sound created a convincing illusion of "realness" that was hard to ignore and easy to love. Which is right? Once more, the elusive ideal is the Boulder's dynamic energy coupled with the Pass's timbral finesse.

On John Gorka's "Can't Make Up My Mind" (Between Five and Seven, High Street 10351-2), producer-guitarist John Jennings's Martin Backpacker guitar solos had a more precise transient attack through the Boulders. The Pass amps transmitted a softer, more "wooden" body tone. Once again, this begged the question: "Which is right?" Like Gorka, I can't make up my mind which is "better"—I value the strengths of each amp. Might as well compare apples and oranges. If I just wanted to enjoy the music, the Pass's natural timbre was wickedly seductive. If I needed to analyze a recording, the Boulder's superb resolution made it the perfect tool for the job. The 500AE is the ultimate pro-audio workhorse amp, while the Pass is a preeminent recreational amplifier.—Steven Stone