Mark Schneider founded Linear Tube Audio, aka LTA, in 2015 to “bring life back to music at an affordable price.” All Linear Tube Audio amplifiers are designed around David Berning’s patented Zero hysteresis, Output Transformer-Less (ZOTL) amplifier technology, and so march to the beat of a very different drum than do non-Berning designs. While the full details of Berning’s patent are beyond the scope of this review, in short, the ZOTL technology does the job typically performed by output transformers: converting the high-voltage, low-current signal from power vacuum tubes to a lower-voltage, higher-current signal capable of driving loudspeakers to sufficient volume levels.

Description

The LTA Z10 costs $4900 USD; add $500 for moving-magnet phono section. It measures 16”W x 5.125”H x 16”D (including connectors) and weighs 18 pounds, and its beautifully finished aluminum case was designed by Fern & Roby.

From left to right on the front panel are seven brass pushbuttons, each with an LED status light: Power, Input, Tape Monitor, Up, Down, Menu/Select, and Back. There are also a dimmable LED display with configurable time out, and two 1/4” headphone jacks, with a little toggle switch for choosing between them: one produces 2W, the other 0.5W. On the Z10’s rear panel are four single-ended (RCA) inputs, one balanced (XLR) input, one pair each of tape input and output jacks (RCA), two pairs of speaker terminals, an IEC power inlet, and the main Power rocker.

Pertinent specifications include a remarkably wide frequency response of 6Hz-60kHz, +0/-0.5dB, into 8 ohms, as well as 18dB of voltage gain and 0.5% THD, both into 8 ohms. Included is an Apple TV-style remote-control handset for controlling the Z10’s main functions. All Linear Tube Audio products are designed and built by hand in the US.

The Z10’s circuit begins with a pair of 12AU7 tubes amplifying the audio signals, which ride on RF carrier frequencies, to very high voltage levels. These signals then pass through a number of small air-core transformers acting as impedance conversion devices. The transformers filter the RF carrier in a manner similar to radio systems, and the audio signals are thus matched to the loudspeaker’s impedance plane, removing the need for output transformers in the signal path. LTA’s website cites numerous advantages for using this approach, including eliminating an output transformer’s leakage inductance and interwinding capacitance -- drawbacks that affect a traditional tube amp’s high-frequency response. Core saturation and magnetizing current are also eliminated, and transformer-core hysteresis is no longer a concern.

The power-amp section -- basically, the guts of LTA’s stalwart ZOTL10 amplifier -- outputs 12Wpc into 8 ohms. This is partnered with a Berning-designed preamp section, a digital control system designed in-house, and the optional MM phono stage. A slew of high-profile parts populates the amp’s interior, including Belleson regulators, Ohno Continuous Cast (OCC) wiring, Vishay Dale resistors for the stepped attenuator, and Mundorf capacitors.

The tube complement comprises four 12AU7s, two 12AT7s, and a quartet of EL84s operating in push-pull class-A/B. All tubes are new old stock (NOS) and are rated to last a remarkable 10,000 to 20,000 hours of use. LTA says this is made possible by the extremely low current levels passed through the tubes -- about one-third the current of typical tube circuits -- which produces far less heat, thereby extending tube life greatly.

Sound

My review sample of the Z10 arrived already run in and with its tubes pre-installed, so setup proved easy. All I had to do was warm it up and settle in to listen. I needed to hear only a few bars of music through the Living Voice Avatar speakers to form my initial impressions, which confirmed the claim implicit in the very name Linear Tube Audio. The Z10 indeed sounded supremely linear, with a smooth, uncolored, evenhanded spectral balance, top-to-bottom coherence, excellent extension at the frequency extremes, and an all-around relaxed sound. This impression held true as I moved to the even-higher-sensitivity Klipsch Epic CF2 speakers. In fact, the latter pairing sounded so linear that it made many other tube amps I’ve partnered these speakers with sound lumpy and bumpy in comparison. I stuck with the CF2s for the rest of the review.

For example, the Z10 communicated the late-’60s-/early-’70s vibe of “It’s a Shame My Store Isn’t Open,” from Natural Child’s Okey Dokey (LP, Natural Child NCRT 001LP), entirely intact, letting through the kick drum’s pleasant roundness and the bass guitar’s warmth while adding no colorations of its own. Guitars and cymbals were also rendered cleanly, devoid of harshness or edge. I’ve heard more than a few similarly priced tube amps lay on doses of their own warmth and richness to produce an excessively thick sound, or crank up the presence region in an effort to add detail -- but the LTA Z10 didn’t editorialize on the sound in any way.

Kruder & Dorfmeister’s landmark electronica album, The K&D Sessions (2 CDs, !K7 7073CD), served as a showpiece for hearing what this meant at the frequency extremes. “Jazz Master” contains plenty of amplitude in the bottom two octaves that can sound muddy and indistinct through the wrong amp -- but through the Z10 the ostinato synth-bass line came through with fine clarity, precise pitch definition, and realistic texture. While it wasn’t the most powerful bass I’d ever heard, all notes were present and accounted for. At the other end of the audioband, cymbals, bells, and atmospheric synths sounded airy and well extended, with clean harmonics and decay components, even if they were slightly dry in absolute terms.

To focus on the midrange I played Anouar Brahem’s Le Pas du Chat Noir (CD, ECM 1792). Brahem’s oud can sound vibrant and well textured through a capable amp, and it certainly did through the Z10. The amp’s midrange transparency did much to highlight this instrument’s tone, making it easy to focus on Brahem’s liquid, introspective touch. François Couturier’s piano also sounded convincingly colorful, with no artificial steeliness or glassiness. The entire album seemed to coax out the Z10’s best -- this amp sounded right at home with relaxed, intimate, small-scale music.

Yundi Li’s disc of works by Liszt for solo piano (SACD/CD, Deutsche Grammophon 474 297-2) challenges hi-fi components of any stripe with its rich harmonics, huge dynamics, and wide frequency range. In the Transcendental Étude after Paganini No.3, “La Campanella,” as the notes run several octaves, from viscerally low to piercingly high, the Z10’s reproduction of them was spectrally balanced and tonally convincing, with outstanding top-to-bottom coherence -- there was not a sour note or spitty distortion to be heard anywhere.

Focusing on the dynamic components of Li’s Liszt, however, revealed an area in which the Z10 came up short. Li hammers the keys in the finale of “La Campanella,” producing a huge, thunderous sound that, through the best amps, can be startlingly visceral. But here the Z10 seemed to narrow this recording’s dynamic range, making it sound less powerful and expressive than I’ve heard it through other amps of similar price. This held true with Digable Planets’ Reachin’ (A New Refutation of Time and Space) (CD, Elektra 3360614144). The deep-bass beats of such tracks as “It’s Good to Be Here” and “Appointment at the Fat Clinic” seemed diminished in amplitude and impact. Ditto Esa-Pekka Salonen and the L.A. Philharmonic Orchestra’s recording of Stravinsky’s The Rite of Spring (SACD/CD, Deutsche Grammophon 002894776198), which also lacked the proper startle factor in the ominous timpani rolls and other percussive strokes, even when played at high volume levels.

The Z10 also left me wanting more in terms of timing and rhythm. With downtempo music -- e.g., Le Pas du Chat Noir -- it was easy to concentrate on such things as instrumental tone and timbre; the LTA was as transparent as could be to such recordings’ acoustic qualities. But with beat-heavy tracks at faster tempi, such as the Digable Planets album, the music lacked some insistence and forward momentum -- it sounded a touch slow. Listening again to The K&D Sessions confirmed this -- that album’s layered, polyrhythmic beats sounded less synchronized in time than I’m used to hearing through other amps.

But through headphones the Z10 sounded fantastic. It effortlessly drove all four pairs I had on hand, sounding transparent, punchy, and eminently listenable, with volume to spare (though none of my headphones presents a terribly challenging load). One compatibility problem arose toward the end of the review period, however: For whatever reason, the Z10 produced a loud, persistent hum through my Shure SE435 earphones. Even at normal to above-average listening levels, this constant hum was at an annoyingly high volume, regardless of volume level or input setting. Wondering if the Shures were broken, I tried my other headphones again -- with all three, the buzz was there but barely audible. But every time I returned to the Shures, it came back in force.

A quick swap to an outboard headphone amp confirmed that the Shures weren’t the problem. A series of e-mails and troubleshooting attempts later, I sent the review sample back to LTA. A thorough check by LTA confirmed that the unit was performing to spec and within tolerances. LTA conjectured that whatever noise I experienced could have been due to interference with the digital display/control system, which LTA says has changed in all current production versions, but the mystery remained unsolved. Perhaps the Shures were simply too sensitive for the Z10 -- indeed, they are, by some margin, the most sensitive headphones I use. If you plan to use the Z10 as a headphone amp, be sure to try your favorite headphones with it before you buy.

Comparison

I compared the LTA Z10 with another tubed integrated: the Lab12 Integre4, which I reviewed in February 2020. Without its optional phono stage, the Z10 costs exactly the same as the Integre4 -- $4900 -- but there all similarities end. While the Z10 uses Berning’s ZOTL circuit for voltage conversion, the Integre4 is transformer-coupled. The Lab12 can produce more than five times as much power: 65Wpc into 8 ohms from its quartet of KT150 tubes. The Z10’s four EL84s are specified to produce 12Wpc at 8 ohms. Still, the proof is in the listening.

First up was Salonen and the LAPO’s recording of The Rite of Spring. The first section highlighted all of the Z10’s strengths: natural tone, realistic orchestral textures, and accurate instrumental timbre and color. Ditto Alisa Weilerstein’s recording of Shostakovich’s Cello Concerto No.1, with Pablo Heras-Casado leading the Bavarian Radio Symphony Orchestra (24-bit/192kHz AIFF, Decca), in which every brass, woodwind, and stringed instrument sounded pure and tonally accurate. In short, the Z10 was a shade more tonally convincing than the Integre4. Chalk up one for LTA.

But in the Stravinsky, once the dynamics kicked in in The Harbingers of Spring, the difference was much greater. Here the Z10 sounded dynamically constricted, while the Integre4 exploded with more bombastic impact and visceral force. This was also true with the Shostakovich -- the orchestra’s volume rose and fell with greater drama and scale through the Integre4. Chalk up one for the Lab12.

In “Act Natural,” from Joshua Redman’s Trios Live (24/88.2 AIFF, Nonesuch), notes in Redman’s dense tenor-sax solo had greater start-stop clarity and insistence, and were more sharply delineated, through the Lab12. Attacks, sustains, and decays were, respectively, also clearer, more fully fleshed out, and longer. This held true with “Mr. P.C.,” from John Coltrane’s Giant Steps (LP, Atlantic/Rhino 7784) -- the LTA Z10 evinced less precision at each note’s leading and trailing edges. Coltrane’s playing and note-to-note connections are sometimes blindingly fast in this track -- through the Z10, these passages blurred together, sounding less distinct from one another, with less edge-to-edge definition than through the Integre4.

The Z10 took a consistent lead in terms of imaging, however, showing its ability to simply “disappear” from the music as it threw solid, lifelike aural images, even with less-than-stellar-sounding recordings. In the Shostakovich concerto, orchestral instruments had greater presence on a bigger, wider soundstage, and sounded more vividly real. The Z10 also did a better job of reproducing the space around individual instruments in a convincingly real and visual fashion, as opposed to a purely aural one. In “What Cool Breezes Do,” from Digable Planets’ Reachin’, the Z10 again showed excellent reproduction of space, with solid images populating a wide, deep soundstage that extended beyond the horizontal plane of my speakers. The Lab12 Integre4’s soundstaging was ever so slightly constricted in comparison, and aural images were not quite as solid overall.

The Lab12 Integre4 proved an interesting contrast to the LTA Z10. The Z10’s clean, extended, flat frequency response was, in my experience, unrivaled for an all-tube integrated, and its imaging capabilities were impressive. Still, it gave up notable ground in musical terms, especially regarding dynamics, momentum, force, and timing.

Conclusion

Linear Tube Audio’s Z10 is a uniquely designed amplifier that bucks conventional tube wisdom. Its sound, too, was unique -- supremely linear, uncolored, coherent, and noticeably more neutral, transparent, and even-handed than any other tube amp I’ve heard. Moreover, it did all of this across a frequency range significantly wider than the norm. As a bonus, it produced beautiful sound from every pair of headphones and earphones I tried with it (though there was the noise issue with the Shure SE435s). Top all that off with a fine user interface, remote control, and a beautiful case, and the Z10 goes a long way toward being a comprehensive integrated amplifier wrapped up in a gorgeous package.

But every amp has its flaws. The Z10’s dynamics are constricted, its timing a bit slow and indistinct, and it lacks ultimate momentum and drive. In those ways it’s bettered not only by the Lab12 Integre4, but by other similarly priced amplifiers. To potential buyers whose musically significant criteria dovetails with my own, I strongly suggest giving the Z10 a thorough hearing. But try to audition it even if you suspect that it might not be your cup of tea -- if only to hear what a tube amp can sound like when output transformers are eliminated from the output stage.

Still, I imagine that the virtues of tube smoothness and liquidity, coupled with unfettered neutrality and linearity, will prove tantalizing to many. And if your musical diet consists mainly of small-scale music -- a girl or guy with a guitar, acoustic world music, or chamber music -- I’m betting you’ll love how the Z10 reproduces it. And to those listeners I say, check out the Linear Tube Audio Z10 first. You might quickly find out that it’s the right amp for you.

. . . Oliver Amnuayphol
olivera@soundstagenetwork.com

Associated Equipment

• Loudspeakers -- Klipsch Epic CF2 (modified), Living Voice Avatar
• Headphones -- AKG K701, Bowers & Wilkins P5, Phonak Audeo PFE122, Shure SE425
• Headphone amplifier -- Schiit Audio Lyr
• Integrated amplifier -- Lab12 Integre4
• Phono preamplifier -- Audio Note L3 Phono Stage V2 with Signature upgrades (modified)
• Step-up transformer -- custom-made Sowter Magnetics 9570 (1:10)
• Sources -- Denafrips Ares DAC; Apple MacBook Pro computer running JRiver Music Center 20, Sony SCD-XA777ES SACD/CD player, Rega Research RP8 turntable with Lyra Delos cartridge
• Interconnects -- Auditorium 23; custom single-core, copper coaxial (RCA); Wireworld Starlight 7 USB and coaxial (RCA)
• Speaker cables -- Auditorium 23, Tellurium Q Ultra Black
• Power cords -- Wireworld Aurora 5.2 and Electra 5.2
• Accessories -- Clearaudio stylus cleaner, Mobile Fidelity Sound Lab record brushes, Music Hall WCS-3 record cleaner

Linear Tube Audio Z10 Integrated Amplifier
Price: $4900 USD; add $500 USD for MM phono section.
Warranty: Two years parts and labor.

Linear Tube Audio
7316 Carroll Avenue
Takoma Park, MD 20912
Phone: (301) 448-1534

E-mail: hifi@lineartubeaudio.com
Website: www.lineartubeaudio.com