AudioAficionado.org - A New Addition -- Luminous Audio Technology Axiom II Passive Preamp

Having virtually completed the GIK-megalithing of my bedroom audio system a few weeks ago with gratifying results, I turned to simplifying its electronics footprint. The system has a single program source: a Windows 10 i7 laptop utilizing JRiver Media Center to play ripped 16/44 and downloaded hi-resolution (24/88 through DSD128 and DXD) files stored on a four-terabyte Seagate USB 3.0 external hard drive. The laptop feeds a TEAC UD-501 USB DAC, which in turn routes its output to the system’s control center via Wireworld Eclipse 7 interconnects.

Until a couple of weeks ago, a c-j Sonographe SC25 solid-state preamplifier with five high-level inputs acted as the control center. While sonically satisfying in that application, it was, like the Counterpoint SA2000 line stage that preceded it, functional overkill for the system. And not just because of the “extra” inputs. Theoretically, at least, the UD-501’s fixed 2.0-volt output should be sufficient to drive my Sonographe SA250 power amp with volume control supplied by a “passive preamp”.

A passive, of course, doesn’t amplify anything. In its purest form, it has no active circuitry or AC line connection—or the noise that piggybacks on them. So less might equal more. “Might”, because just sticking a potentiometer between the DAC and the amp could yield a worse sonic result (such as thin bass or constricted dynamics) than that achieved with an active preamp in place due to, among other factors, an output/input-impedance mismatch with the power amp. Could I find a passive that “fit” my system…without destroying my fragile piggy bank?

After spending about a week scouring the Web for product descriptions and reviews to determine my options, I ordered a Luminous Audio Technology Axiom II single-input/output passive. The Axiom is available in several versions ranging from the base single-input/output model featuring an Alps “blue” pot and Holco resistor to a pricier 1%-precision 48-step-attenuator unit and up to three sets of input jacks. I ordered the base model with the $25 Caddock resistor upgrade and supplied designer Tim Stinson with my DAC’s rated output voltage, amp-sensitivity and -input-impedance, and speaker sensitivity specs so he could tailor the passive to my system. Cost: $220 for the passive, $19 for two-day Priority Mail shipping from Virginia to Oregon—and, bless the USPS, the Axiom arrived on schedule.

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The unit’s construction is solid, with spot-on fit and finish. The long-barrel RCA jacks on the rear panel accommodated my Wireworld interconnects without any spacing hassle or “give” to the chassis when I attached the cables. Turning the Alps pot revealed silky-smooth operation.

Tim recommended 72 hours of burn-in for the Caddock, so I fed it the frequency-sweep tones ripped from my Sheffield/XLO Test and Burn-in CD on endless repeat for that period. For my first listen following burn-in, I auditioned…silence.

That’s right. With the laptop, external drive, DAC, and amp powered up , I put my ear to each Paradigm Studio 20. With either the SA2000 or the SC25 in the equipment loop, I could hear just the faintest hint of 60-cycle hum through the speakers even with the volume control turned all the way down. With the Axiom in the circuit and the pot turned up to 12 o’clock? Dead quiet. A good start.

My listening fare included a selection of classical, jazz, vocals, film scores, opera, and choral works. The characteristic that stood out in each case was transparency. In spades. That applied to instruments, voices, and even the space in which the artists either performed or were placed by the mixing process. I attribute it at least in part to the “blacker” background perceptible with the Axiom versus either active preamp in the equipment loop.

First up in the playback queue was the reading by Eiji Oue and the Minnesota Orchestra of the final movement of Aaron Copland’s Third Symphony (Reference Recordings, 16/44 rip), which offers a good test of both bass response and dynamic breadth. Nothing anemic or compressed here. Moreover, the bass drum and timpani whacks revealed more “skin” than heard with either “active”, and brass emitted a richer, fuller sonority. So far so good.

A DSD128 reissue of Ernest Ansermet’s performance with the Orchestre d’ Suisse Romande of Claude Debussy’s “Iberia” (Decca) dispelled any notion that the Axiom would thin or “dry out” massed strings, rendering them as liquid and wholly in keeping with the sensuous nature of the score.

One of the most demanding massed choral tests I know for an audio system is the raucous “What a Day for an Auto-da-fé” from Leonard Bernstein’s final iteration of “Candide” (Deutsche Grammophon, 16/44 rip), a production in which DG’s engineering team seemed intent on littering the soundstage with shattered glass. The Axiom—particularly its Caddock “engine”-- is not at all forgiving with the piece. But the various choral choirs that “editorialize” on the gory proceedings it depicts are more precisely rendered in both location and internal composition than I’ve heard previously. Same with the long-suffering soloist (Adolph Green) recounting the “gift” bestowed on him by the “charming” Paquette.

Toning things down a bit with Stan Getz and Charlie Byrd in “Jazz Samba” (Verve, 24/96), I was struck by the full-bodied breathiness of Getz’s tenor sax in “Desafinado” and the nuanced finger-work of Byrd—strongly hinted at with the “actives”, but more pronounced with the Axiom at the control helm.

Is there anything wrong with the Axiom? Nothing I’ve yet discovered. From an aural perspective, left-right balance (there’s no balance control on the Axiom) is spot-on, indicating that the Alps “blue’s” channel tracking is gnat’s-eyebrow precise. I’d note that Tim Stinson was a bit conservative with his burn-in recommendation. At somewhere between 85 and 90 hours, the system with the Axiom in place “broke out” with a more expansive, better-defined-internally soundstage (on those recordings not panned to imprison the performers in the respective speaker enclosures), tighter bass, bloomier midrange, and more liquid top end.

So I’m as happy as a clam with the purchase.

Of course, I then decided to put four Stillpoints Ultra Minis under the laptop and a pair of cork-and-rubber vibration-control cubes under the external USB drive that supplies all the music.

But that’s another story…

Jim