Pass Labs Aleph 3 power amplifier Page 4

There is no comparison
I did listening comparisons with my home-built pair of Zen monoblocks. The Zen is also a Nelson Pass design, published in The Audio Amateur in issues 2 and 3 of 1994. It is also a Nelson Pass design, though it was conceived more as a curiosity than as a finished commercial product. The Zen is the only amp in the world with fewer gain stages than the Aleph 3—just a single MOSFET.

To cut to the chase, the Aleph 3 sounded better. There was a definite family resemblance between the two—that friendly coherence that all good single-ended amps seem to convey—but the Aleph 3 had noticeably less coloration and distortion. To their credit, the Zen did have a tiny bit more of a certain purity, which I attribute to its single gain stage consisting of a single device, though I can't be certain of this. However, the Aleph 3 was marginally superior in all other areas of reproduction. It sounded more dynamic, had deeper bass, a larger soundstage, and a touch more clarity. So the Pass amp passed its first test, but now I'll have to figure out more ways to improve the sound of my Zens. Darn.

Mark Levinson & Quicksilver comparisons
I've been living on a steady diet of single-ended transistor power amps, praise Allah, for over a year now. Wanting to make comparisons with a couple of Stereophile-ranked Class A amps, I did side-by-side listening comparisons with the Aleph 3, the Mark Levinson No.333, and the Quicksilver M-135 monoblocks. The No.333 was graciously lent to me by ListenUp Audio in Boulder, Colorado, and the folks at Moondance Sound & Cinema in Denver were nice enough to lend me the Quicksilvers.

For these comparisons I made a special pair of interconnects with resistors soldered to them to eliminate the preamp from the circuit and increase resolution. The resistors reduced the size of the signal coming from the Rotel RDP-980 D/A so that it could be fed directly to the power amps. The Audio Electronics AE-2 is quite transparent as preamps go, but two high-quality resistors are more transparent still.

The Levinson No.333 utilizes bipolar instead of MOSFET transistors. Its circuitry is much more complicated than the Aleph 3's, and its output stage operates in push-pull. The No.333 lists at $8495, nearly four times the price of the Aleph 3.

First up for listening was the title song on the Living Colour compilation Pride (Epic EK 57698), a well-recorded studio creation. The 1995 digital remastering of this track, which originally appeared on Time's Up (Epic EK 46202), noticeably improved its sound. If only they had remastered the entire album! Right away it was apparent that the Levinson did not present as much detail as the Aleph 3 did. Vernon Reid's unbelievably fast fingers sounded less superhuman through the No.333. His rhythmic subtleties on the guitar did not sound as impressive. The bass on this big amp was very impressive, though. It was not too exaggerated, just very strong and solid, increasing its relative position in the musical hierarchy. In the other frequency ranges, however, this amp did not serve the music in quite the wonderful way that the Pass amp did.

Next came Astor Piazzolla's Suite Punta del Este, from ¡Tango! (Dorian DOR-90201), performed by the Camerata Bariloche of Argentina and featured in the incredible Terry Gilliam film Twelve Monkeys. This purist-miked, live to 20-bit digital recording made it even more plain what the Levinson was doing to the music. It imparted a slight but persistent artificial quality to everything played through it. It was a little metallic, changing instrumental timbres and hardening the texture of the whole ensemble. The woodwinds sounded less woody, it was harder to feel the pressurized air shaking the bandoneon's reeds, and the solo violin sounded too wispy. In addition to this, the Levinson's soundstage was not as large, and the hall reverberation was less audible. Nor were its microdynamics as fast or as natural.

If the No.333 had to be characterized with one phrase, it would be synthesizer-like. It gave a somewhat Technicolor presentation of music, superficially dramatic but missing some of the juicy harmonic body that can be enjoyed from this Dorian recording. This is, of course, in comparison to the sound of the Aleph 3. In comparison to other amplifiers, the Levinson may very well sound natural and open, but after becoming accustomed to what the Pass amp could do, I just didn't want to keep listening to the Levinson for very long.

Now for the tube amp. Tubes have a mystical reputation among many audiophiles, part well-deserved, part superstition. It's true that, in general, tube amps tend to have simpler circuits than do solid-state amps, though this is not true with the Aleph 3. The Wavelength Cardinal is the only tube amp I am aware of that, like the Aleph 3, has just two gain stages. Tube amps also require an output transformer (footnote 2), which is an awful lot of wound-up wire to be putting between you and your music.

I wanted to use one piece of music as a reference point for all three amps, so out came Piazzola's Suite Punta del Este again. Immediately noticeable was the round, warm character that reviewers often write of with tube amps. There were quite a few frequency-response colorations that the Pass Aleph 3 did not have, but I won't mention these as they appeared to be very system-dependent. After some time it became clear that these amps did not reveal as much detail as the Pass amp. This was not just a matter of more or less treble; the Pass uncovered more information in the midrange and bass as well. On the Piazzola the M-135s' slightly muffled quality was definitely a negative. It is much more enjoyable to have such a fine document of a musical event reproduced transparently, so you can enjoy all of the small, artful touches that only truly great musicians can provide. Only the Aleph 3 was so transparent; neither the No.333 nor the M-135s allowed as much of the music to pass through intact.

Footnote 2: Tube power amplifiers need output transformers to couple their high impedances and voltages to speakers, which operate at low impedances and lower voltages. There are a few output-transformerless (OTL) tube amps on the market, but these are rare exceptions.—Muse Kastanovich
Company Info
Pass Labs
21555 Limestone Way
Forest Hill, CA 95631
(530) 367-3690
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