February 2021

Linear Tube Audio Z40 Integrated Amplifier Review
Plus notes on LTA's ZOTL Ultralinear Integrated.
Being true to the music.
Review By Dr. Jules Coleman

  It is commonplace that audio reviews, including this review of the Linear Tube Audio Z40 vacuum tube integrated amplifier, should describe the sonic characteristics of components under review, assess the desirability of those attributes, and offer an overall evaluation of the product: e.g. is it worth a serious listen, might it be worth considering for purchase, and so on. The viability of a review depends on the reliability and credibility of its descriptive aspects and the good faith in which the recommendations are made. So before we get into my review of

Overall, reviewers may lack craft, but not integrity. We mean for our reviews to be reliable reports of what we hear and good faith assessments of the musical persuasiveness of the products we review. But what is the basis of our confidence that our intentions are generally realized?

Certainly, a large part of the answer to that question resides in the process we follow in reviewing equipment. Nearly all of us follow what I call 'reference system reviewing' (hereafter RSR). This process is constituted in part by protocols governing three areas of the process: those governing:

1. The construction of a reference system;

2. How reference systems are to be employed in the review process; and 

3. The inferences that can be reasonably drawn from properly executing the review process. (Because the RSR protocols are drawn from practice, my list of them may be incomplete and very likely contestable.

I will try therefore to describe them generally so as to allow for variations and to limit my discussion to the most basic, and hopefully, least contestable of them.) Let's take a brief look at some of the most significant of these protocols in each category.

The protocols for creating a reference system call for putting together components that individually are sufficiently revealing of up and downstream components and that collectively provide musically persuasive listening experiences. What counts as musically persuasive will depend on each reviewer's audio aesthetic and that is why explicitly acknowledging one's aesthetic is essential if reviews are to be as helpful as we intend for them to be. Once a reviewer judges that they have a system that is sufficiently revealing and musical, they have a responsibility to keep the system as is – but for minor adjustments – for a sufficiently long period and employ it consistently over time in their reviewing so that they and their readership become familiar with its sonic characteristics.

The protocols for employing the reference system for reviews govern both what components are reviewable – given the reference system – and how reviews should be executed. If you have an 8-Watt SET amp as part of your reference system, you don't accept opportunities to review Martin-Logan electrostatics, Apogees, or multi-driver box speakers with complex crossovers. Avoid obvious sonic mismatches.

As for execution, once a new component comes in for review, it is substituted for the reference component (or components) that serve the same or appropriately similar functions in the reference system, while leaving everything else in the reference system in place. The goal of this strategy is to isolate the review component's sonic contribution – whether for better or worse. After an initial listening period, a reviewer may make changes as necessary to dial in the new component in the context of the system. (Over the course of listening further minor adjustments may be needed and are, within limits, permissible.) The reviewer then listens to the newly constituted system for a sustained period of time with a variety of music (hopefully limiting the time devoted to listening to audiophile recordings). As the reviewer begins to form a view of what they hear, they may re-insert the reference system component primarily for the purposes of testing – confirming or invalidating their tentative opinions. This process can repeat over a fixed period of time until the reviewer becomes sufficiently confident of what they are hearing.

The protocols governing conclusions upon completing a properly executed review set out the character, quality, and quantity of evidence required to justify one's claims about the sonic characteristics of the component and one's overall assessment of it. Where do these protocols 'come from' and what is the source of their authority: that is, why should reviewers follow them?

The protocols governing are not issued by some authoritative body charged with responsibility for doing so. They evolve over time. Their normative force comes from two related practices: the practice of complying with them, and the practice of adopting the protocols as the explanation of why reviewers comply and as the basis for criticizing those who do not. Together these practices establish the protocols as authoritative over those whose behavior they intend to guide. Presumably, reviewers would not accept the protocols as norms governing what they do if following them led their reviews astray: if, in other words, they proved unreliable or otherwise unsuccessful.

The heart of what we do as reviewers as well as its credibility and usefulness is very much connected to the shared practice of RSR. I have long nurtured doubts about RSR. The sound one hears from a system is the sound of the system, taken as a whole. If the sound one hears is always the sound of a system, then, a fortiori, the sound of the reference system is the sound of that system taken as a whole as is the sound of the system with the review component inserted. Differences between them are differences in the sonic character of the systems.

The basic premise of RSR is that by keeping the rest of the system as is while replacing one component with the product under review, we have isolated the cause of whatever changes in sound occur. It's true that the change in the sound is caused by inserting the review component into the system, but that change can be caused in at least three different ways. First, the difference in the sound of the system is due to the sound of the review component. In other words, what one hears is the sound of the review component. Second, the difference in the sound of the system is down to the impact the review component has on the performance of the other components. Third, the sound of the system is the result of both aspects of the sonic characteristic of the review component itself and its impact on the performance of other components.

If fit matters when putting a band, a basketball team, or a relationship together, it's ludicrous to suppose that it doesn't happen in putting an audio system together. Audio is not immune to the effects of synergies. Fit matters. The evidence supplied by even a well-executed review process equally supports one of three different hypotheses: the sound one hears reveals the sonic characteristics of the reviewed product; the sound one hears reflects the interplay of the review component on the other. The practice of replacing only one component/review is meant to isolate the contribution of that component. In principle that practice isolates the cause of differences in the sound of the system. The problem is that there are different ways in which the component can cause a change in a system's sound, only one of which is through the distinctive sonic characteristics of the review component.

A lot more work would have to be done to isolate the causal mechanism at work or to raise one's confidence that the sound of the review component has a particular set of sonic characteristics. Almost certainly that additional work would involve placing the component in several different 'systems.' RSR on its own is not up to the task.

None of this means that there is no value in settling on a reference system – whether you're a reviewer or an audiophile. If you insert a component into your reference system and the sound deteriorates (by your lights), then you have a good reason not to replace your current component with it. Of course, the evidence is compatible with deciding to keep the component and getting rid of everything else, in effect, taking on the task of building an entire system around it. Normally, however, convenience and cost will win out.

What conclusions, if any, should we draw?

It may be that RSR is the best we can do given available time, financial resources, interest, and more. In that case, we should take a somewhat more modest stance about what our reviews can establish. There is no reason, however, not to explore alternatives to RSR. Even if there is no perfect alternative to conventional practice and its protocols, there may be viable alternatives to RSR. Whatever the outcome of experimentation, it is good practice periodically to make sure that the practices we have in place, and the norms we follow, are the best we can practically do.

One approach would be to abandon reviewing individual products altogether, focusing our attention on reviewing systems taken as a whole. This approach would create problems of its own, is difficult to execute, and would offer no obvious way of disentangling the contribution of the component's parts. On the other hand, I see no reason why especially senior reviewers with a great deal of experience should not from time to time undertake to do precisely that. System reviews would remain a small portion of the overall review universe, but nevertheless an interesting and potentially helpful one. If carried out by those who are particularly good at vivid characterizations of sound, they will at the least provide for interesting reads.

I am sure there are a number of other alternatives, some of which I have considered and set aside in favor of an approach based on what I refer to as the 'best light' approach. Roughly, the general idea is that the most informative reviews are those undertaken with the intent of capturing the sound of a component and judging its performance in the most favorable circumstances: under the conditions where it is set up to succeed, to reveal its capabilities rather than its limitations.

I came to this approach as a result of two experiences that on their face have nothing to do with audio. First, as a university professor for over 40 years, I learned, especially in graduate seminar settings, that most students were comfortable with and soon became very good at presenting objections, finding flaws and faults in arguments – especially other peoples' arguments, even the arguments of distinguished authors whose careers of achievement these students would never be able to approach. To be sure, finding flaws and shortcomings helps to sharpen the mind, though it is a tool best employed on one's own arguments, which is a much less frequent object of self-conscious reflection.

As a result, I adopted the teaching strategy of getting a feel for which point of view or side of an argument particular students were most opposed to. At that point, I assigned to each the responsibility of defending the position that they least favored against the very best objections to it that they could devise themselves or which had already existed in the literature. I made each student a veritable defender of the opposing view for the entirety of the course. I rarely let them know precisely my intention. I did let them know that they would be graded by the quality of the objections they raised and their ability to fend them off. My minimal goal was to force them to see the arguments they all too easily dismissed in their best light.

Like many of you, I have played sports and watched the best at various sports perform, sometimes in person, but often on television. I have been struck by how often the manager or coach of a team characterizes his or her responsibility as putting each of the players in the best position to perform at their best: wanting to get the most out of them. Of course, there is value in determining a component's limitations, just as there is value in determining the limits of various arguments (especially one's own). And the manager of a baseball team surely needs to know when a player's performance is likely to suffer if his aim is to put the player in the best position to flourish and excel.

In putting together an audio system, one's goal is to find an optimal fit of components, and staying within the framework of components that work well together is the best place to begin. With the limited time available for reviews, we are not likely to do better than that. In addition, assessing a component's performance under what the designer or manufacturer takes to be a favorable environment is not only fair, it reduces a reviewer's vulnerability to certain forms of criticism.

How does one employ this approach in practice?

I can only answer by explaining how I have chosen to start doing so. I have several components in house and I have a system comprised of some of them that I enjoy listening to. It's not a perfect system, but it works for me. I don't treat it as a reference system for the purposes of review.

As a first approximation, I divide components I might be in a good position to review into front and back ends (sources and speakers) on the one hand and electronics on the other. I don't feel particularly well-positioned at this point to review interconnects, cables, and power conditioners going forward. I have decided to begin my new journey by focusing on preamplifiers, amplifiers, and integrated amplifiers. With that in mind, I picked out three speakers I had on hand and two sources. The speakers are Auditorium 23 Solovox (an open baffle design with a complex (non-enclosed) cabinet, the Magnepan 1.7i, and LSR planar speakers. My sources would be Mytek's most recent version of the Brooklyn Bridge for all things digital and the newest Well Tempered Turntable. Unfortunately, the pandemic has caused delays in the arrival of the newest WTT, but the loss was made up for by the kind folks at VPI who loaned me a Reference table with carbon fibre arm in conjunction with my upcoming review of the Grail phono stage. I set all my electronics aside.

I had the front and back ends covered. The question was where to begin with the components that reside in between.

Linear Tube Audio Z40 Integrated Amplifier
A good friend of mine, Jay Bargmann, who is both a successful, distinguished architect and an unrepentant audiophile had put together a quite impressive audio system built around a Linear Tube Audio Ultralinear amplifier and a pair of Spatial Audio open baffle loudspeakers. Friends who had heard similar configurations at various audio shows spoke well, often glowingly of the results of LTA / Spatial audio pairings. When Nicholas Tolson and Mark Schneider (the folks running the show at LTA) offered Steve Rochlin the opportunity to review the brand new Z40 integrated amplifier, I jumped at the opportunity to review it.

Absent a reference system, and having adopted the best light approach to reviewing, I contacted Nicholas Tolson at LTA to see if he had a particularly good experience with other components mated with LTA electronics. Unsurprisingly he mentioned the Spatial Audio speakers and Paul Speltz's Anti-cable interconnects and speaker cables. With Nicholas's help, I was able to secure a full complement of Anti-cable interconnects and speaker cables from Paul, though he had no power cables to spare at the time. I was impressed by some modestly priced Audience power cords that I had recently reviewed and purchased several of them. Without hesitation, I substituted them for Speltz's power cords as I had caught a glimpse of LTA equipment being paired at shows with Audience power conditioners.

Despite Jay's efforts, I was unable to secure a review pair of the Spatial Audio speakers, though I was promised a pair to review at a later date. Had I received a suitable Spatial Audio speaker I would have gladly mated it with the LTA Z40 in place of my Solovox. On the other hand, I was confident taking on the LTA for review in part because I had reason to believe the manufacturer was comfortable with pairing his amplifier with open baffle speakers. The Solovox would likely do just fine. If not, I was determined to get back to the folks at LTA for other recommendations. As it happened, the need to do so did not arise.

John McGirk, distributor for van DenHul products soon arrived with both the Grail phono stage and a loaner Reference table from VPI. Everything was set for the arrival of the LTA Z40.

LTA: The Back Story
Located in Takoma Park, Maryland in the greater Washington DC area, LTA was founded by audio enthusiast Mark Schneider. The company is a relative newcomer to the market but produces a range of audio products from headphone amps to preamps, amps, integrated amplifiers and power supplies. Their best-known products are probably their headphone amps and the Z10 integrated amplifier that has been featured at many audio shows to near universal positive acclaim.

The most interesting fact about LTA is that the circuits for most if not all of their electronics – amps, preamps and integrated amps -- are David Berning designs. For those of you unfamiliar with David Berning, he is widely recognized as one of the truly great creative designers of audio circuits. For years he produced components under his own name, and many remain prized possessions and are sought to this day: not just because they were designed by a living legend, but because they continue to sound great. Berning is and remains an iconoclast. He is genuinely admired for his creative genius and uniqueness of his designs. Best of all, in addition to being technical marvels, his designs work.

All Berning amplifier circuits with which I am personally familiar are transformer-less designs. Strictly speaking these designs are called ZOTLs. Historically, some OTLs, especially those associated with Julius Futterman, were viewed as near perfect matches for electrostatic speakers – especially the original Quad 57s, in spite of their notoriously unfriendly loads.

Whatever the sonic virtues of OTL designs, their potential remained difficult to realize in practice. Often, they required banks of tubes running at full capacity to produce sufficient usable power. Keeping all the tubes biased correctly was often a daunting task. The half-life of tubes running full out was nasty, brutish and short. Owning an OTL was a bit like owning a La Pavorini espresso machine: a labor of love punctuated regularly by great frustrations. To make matters worse, the typical OTL would run exceedingly hot, so much so that a good sized OTL could heat a large listening room in winter. On the other hand, it could make audio listening in the summer months less inviting. To survive the experience, one would have to turn on all available air conditioners at full blast. The noise the air conditioners made certainly made critical listening considerably more difficult during the summer months.

Berning resolved to design transformer-less amplifiers that would overcome all of these problems. His ZOTL circuits required many fewer tubes to generate the necessary power levels. His designs worked with tubes of many different varieties thus increasing the audio flavors that listeners could taste and choose among The tubes in a ZOTL circuit run much cooler and last significantly longer. In short, if there are distinctive virtues that OTL style amplifiers have that cannot be matched by amps that require transformers, Berning's designs allowed the audiophile to secure those virtues without enduring the pains and inconveniences of standard OTL designs.

LTA licenses Berning's designs. In addition, while new products are in pre-production stages, they are often brought to Berning for comment and suggestions. At least in this minimal sense, he stays involved in the design and manufacturer of the product. They do not bear his name, however, and so strictly speaking they are not his to answer for. On the other hand, LTA is allowed not merely to employ his designs, but to use his name in marketing their products, and so it is easy to see why Berning would want to keep an eye on what the good folks at LTA produce. This can only be an additional benefit to them.

The design team at LTA obsesses about parts quality. Belleson regulators, Mundorf caps and Vishay resistors, high purity copper wire, rarely standard fare in anything other than higher-priced gear are included in the Z40. Parts quality matters sonically and LTA amps make the very best of the Berning circuitry. They do so in a package of subtle elegance.

Prior to my time with the Z40, I had some experience with transformer-less amplification. Like many others at audio shows, I also found myself invariably drawn to the Atma-Sphere audio rooms, which rarely failed to entice and reward extended listening. I have owned two OTL amplifiers, one of which all too briefly. I had in my possession an original Futterman OTL – including its mechanical noisy fan -- that he personally had gifted to the NY expressionist artist Larry Poons, who in turn gifted it to the now-deceased art dealer Renato Danese who gifted it to me only to have Poons ultimately asked for its return. I attempted to trade it back to him for a painting, but as is often the case, both my negotiating skills and my legal training failed me. I was quite anxious to receive the Z40 for review.

Looks Good
Though a relative newcomer to the industry, LTA displays professionalism one normally associates only with the most venerable and venerated brands in the industry. The Z40 arrived on the promised date. The unit was well packed and secure, more than able to handle the various forms of mistreatment shipping companies are capable of.

The Z40 is housed in a minimalist industrial design made of aluminum and created by award-winning designers Fern & Roby. There is nothing ostentatious about the design. Yet it offers some nice aesthetic surprises, notably the tops of the four KT77 power tubes that extrude from the upper left side of the casement. I liked the look a lot. I am a fan of reserved confidence in all things. In audio, this takes the form of letting the music speak for the product rather than having a gaudy, glossy, over the top box do so. I find nothing of aesthetic interest in the contemporary home designs that dot the foothills of Bel Air, Los Angeles that look more like corporate headquarter buildings with their heliport roofs. The latest bling in audio casements are equally ostentatious and give the impression of trying to distract one's attention from the sound they produce.

It's probably a failing of mine, but I rarely comment on the layout of the front and back panels of any audio component. I found the layout of the Z40 front panel incredibly attractive, easy to access and use, and in great overall aesthetic balance. A lot of thought went into making it so functional and attractive. It was as pleasant to the touch as it was to the eyes. The front panel features 100 stepped volume control, seven brass touch switches for power, input, tape, up / down, menu / select, and back. It boasts a headphone speaker switch in addition to dual headphone outputs.

The back panel is incredibly well-organized. Power cord connection and on / off switch to the left followed by tape monitor in and out inputs (RCA) followed by four additional Cardas RCA inputs and one balanced input using two XLRs. The speaker outputs are aligned below the RCA inputs. All very rational and very easy to access. The unit is 17" wide, 16" deep and a hair over 5" tall. It weighs about 18 pounds.

The Z40 integrated comes in two forms: one that includes a MM / MC phono stage and one that does not. The unit I reviewed did not include a phono stage. It is worth noting that the phono stage includes a Lundahl step-up transformer, which in my experience is very good and simply increases the overall value of the Z40 making it an even more versatile unit – and a significant value.

Because so much of my serious and critical listening sessions are dominated by records, I am personally less drawn to a full-function integrated amplifier than others might be. In the past, I often supplemented even full-function preamps with step-up transformers that were specifically matched to my cartridges of choice. I was by no means disappointed that the review unit was line stage only, but it does mean that I did not have an opportunity to listen to the performance of what I suspect is a very capable phono stage.

Into The System It Goes
For much of the reviewing period, the system consisted of the VPI Reference turntable, outfitted with carbon fiber arm and van den Hul moving coil cartridge, Van den Hul Grail and Lejonklou Entity phono preamps, LTA's Z40 and Zotl Ultralinear integrated amplifiers, Auditorium 23 Solovox open baffle, as well as Magnepan 1.7i planar speakers. Connections were all provided by Anti-cables. The majority of my listening took place with the Z40, Grail, and Solovox combination. Other components were employed both to confirm initial listening impressions as well as to judge the extent to which the LTA integrated amplifiers could be used with Magneplanar speakers.

I resisted for the most part delving too deeply into my record collection. Doing so would introduce the Grail or Entity into the system and I wanted to avoid doing that at least until I had drawn some tentative conclusions about the LTA. I found myself drawn to the conveniences and the extensive library that the Brooklyn Bridge makes available. Once I dialed in the sound, I listened in this basic configuration for a bit more than two months before making any changes, though I tinkered a bit with speaker placement now and again to fine-tune imaging, soundscaping, and overall tonal balance throughout the review period.

Sounds As good As It Looks... Only Better
Before listening to the Z40, I had formed a tentative opinion about the general character of transformer-less amplification based on a reasonable sample size. It is always risky to form opinions about 'amp', 'speaker', or 'turntable/arm' or 'cartridge' types, but most of us invariably do so. I am no exception. Everybody's got a view about horn loudspeakers – whether or not they have ever heard any. Almost everyone has a view about direct-drive turntables, acrylic anything, tubes, solid-state: you name it. It's ok to have preconceived notions in many (but not all) parts of our lives. It reduces search costs and simplifies decision making. Even so, It helps to have at least some evidentiary basis for one's preconceived notions. One has to be prepared for surprises and to be open to changing one's mind (those familiar with my academic work – especially on corrective justice – know that I have no trouble changing my mind: and in doing so again). And one has to be capable of admitting mistakes (much more difficult to do).

Given how few OTL amplifiers are produced and sold, I would characterize my experience with them as reasonably broad. I thought that it might be a good exercise to jot down my thoughts about their general character based on my experience, prior to the arrival of the Z40. I did this for two reasons. In an occasional moment of unexpected self-awareness, I wanted to see if I had any deeply rooted preconceived notions about OTLs; and if so what they were. I also wanted to be able to identify a baseline that would allow me to draw contrasts, if any, between other OTLs with which I was familiar and transformer-less amplifiers based on the Berning patents.

It turns out, I had more thoughts about my previous experience with OTLs than I expected. And I had one overarching conclusion: namely, that I have a great deal of difficulty characterizing the overall sonic characteristics of the OTLs I have heard. In the end, that is because so many of their attributes cut both ways.

For example, the absence of a transformer contributes to a certain immediacy and transparency on the one hand, and an absence of weight or heft on the other. The extent of the transparency is startling, the access to micro dynamics and micro details nearly unrivaled, yet the presentation often lacks a capacity to provide nuanced tonal shadings. The presentation misses nothing but sometimes fails to develop anything – especially harmonics – fully. When they fall short it is because they come across as white, light and spot lit. For all their immediacy and dynamics, they can display a certain coolness, distance and come across as a bit disinterested, less than fully engaged.

Before listening to the Z40, I would have to say that I felt about transformer-less amplification the way I feel about people, including myself: sometimes our greatest strengths and virtues are also our greatest vulnerabilities and weaknesses and the source of our most painful disappointments.

Three months with the Z40 changed all that. Note that it's taken my psychiatrist far longer than that to transform my self-perception, and to have made a dent in my perception of others. And at a far greater financial cost mind you. David Berning is rightly praised for having solved a set of serious problems that have made it difficult to execute in practice the ideal of an OTL amplifier. Wirth their Z40, LTA has gone a significant distance towards redefining the sonic signature of transformer-less amplifier.

Tell me More
The Z40 comes fitted with KT77 power tubes. The KT77 is a kissing cousin of the EL34 tube. For a premium, you can purchase the Z40 with premium Mullard XF2 EL34 tubes. The EL34 is often described as a midrange tube: harmonically complex, rich, and full-bodied. In some circuits, it can present a warm, full and weighty tonal balance. It is not known for a kick-ass driving bottom end or mid-bass or for a particularly extended top end. It lacks the drive of the less well-known EL84, and the weight of a good 300B tube. The EL34 is not rounded in its delivery, but it lacks sharp edges as well. In my experience the EL34 tube makes music and its presentation is natural, accessible, dense enough, but not especially revealing of microdynamics, inner detail, or harmonic shadings. But everything depends at the end of the day on the circuit and the parts.

I had only modest experience with the KT77 and had no basis for forming an opinion of its characteristics. I asked around and friends far more familiar with the tube than I am indicated that it was just like at EL34 but a bit less in every respect.

Given my prior experience with OTL designs, this gave me pause as I worried that a less rich and dense midrange tube combined with an OTL's proclivity to present, white, light, and spotlit would amount to a lost opportunity to bring needed heft and harmonic fullness to the amp. I briefly considered asking LTA to send me four EL34s to replace the KT77s. In the end, I decided not to as my responsibility was to review the integrated in its stock configuration (perhaps I should have requested a set of EL34s for additional or comparative listening, but I did not. A missed opportunity no doubt).

My concerns quickly proved unwarranted. I made good use of the Brooklyn Bridge's extensive library which allowed me to indulge my all over the map musical tastes. The combination of the Z40 and the Solovox rewarded me with enjoyable hours of listening on a daily basis. Let's get to the basic characteristics of the Z40 sound.

I was fortunate to have a lot of experience with the Solovox loudspeakers. All of it, but for one exception at the time, involved very high-quality Shindo electronics of a distinctive voicing in several different flavors. I had mated the Solovox in prior times with Shindo'sCortese, Sinhonia, and 300B Ltd amplifiers. The sound, in every case, identifiable as in the Shindo voicing differed in some discernible ways. The Sinhonia provided the most driving dynamic voicing, the Cortese the most subtle, shy, and nuanced. The 300B Ltd the richest, most dense, palpable, harmonically involving, and weighty. Part of my ability to make out these differences is owed to the Solovox speakers.

No longer available the Solovox is a single driver very complex open baffle design. They are fitted with a PHY -HP full range driver customized for use in Keith Aschenbrenner's range of open baffle speakers. With the unexpected passing of PHY-HP's designer and owner, Bernard Salabert, and subsequent supply concerns, Aschenbrenner moved from open baffle designs to horn loading speaker enclosures featuring Line Magnetic versions of original Western Electric drivers, including the renowned WE755.

I have yet to hear a better full-range driver than the PHY-PH as customized for Auditorium 23 speakers I have yet to encounter a speaker more capable of recreating the dynamic realism of live music than the Solovox.

I felt comfortable in the conclusions I was able to draw about the contribution the LTA Z40 integrated made to the music I was hearing. In a nutshell: The most striking feature of the Z40 is its overall balanced and musically persuasive presentation. This feature is hard to describe since it is more of a conclusory judgment than the identification of a particular attribute. Nor is it just the summation of a set of attributes taken individually. Rather it speaks not only to particular attributes, but also the manner of their integration into a distinctive signature presentation. This balanced and invariably persuasive presentation offers one extraordinary and rare virtue. The LTA is convincing on all forms of music. It is among the most honest amplifiers I have experienced.

Now to particular attributes: I was impressed by the amp's dynamic drive, the density of presentation and of particular musical details, as well as its capacity to reveal subtle tonal and dynamic shadings.

In my experience, different amplifiers, no matter the system in which I have heard them draw attention to one or another range of the musical spectrum. Everyone notices these features, but it is more interesting to note the different ways in which amplifiers (and speakers) do so. The most obvious way is in the form of what comes across almost as a difference in relative volume. Some setups make it appear as if the volume has been turned up on the bottom octaves or, god forbid, the upper midrange. The apparent volume disparity is a kind of non-linearity. My ears are even more sensitive, I believe, to differences in the density of certain notes drawn from different ranges of the musical spectrum. I have experienced this most often in the lowest and highest octaves. Sometimes the bass is big and weighty: almost fat. But the notes aren't dense. They lack muscle and density. Instead, they sound like blubber.

The opposite occurs at the higher frequencies. I know I am in the minority in not appreciating the presumed virtues of 'high-end' sparkle, but my experience is that sparkle is usually accompanied by the absence of density and weight in the higher frequencies. High doesn't mean light. And transparent shouldn't mean see-through. Too often the presentation of the high frequencies is ephemeral, see-through, nearly intangible.

The LTA, in contrast, exhibits the virtues of the very best amplifiers. Music is appropriately weighty, dense, and harmonically developed. Most importantly, these attributes are carried through equally from the lowest lows to the highest highs and all stops in between (as best I can tell given the frequency limitations of the Solovox. One reason why after a couple of months I substituted the Magnepan 1.7i and eventually the LRS for the Solovox.) This even-handedness is incredibly rare.

In addition to its superb drive and even-handed approach to the density of its presentation across the musical spectrum, the LTA stood out for its general way with music. I once reviewed a turntable that kept time perfectly, but in the manner of a large army marching in step. It exhibited no soul; no bounce in its step; just the unrelenting thud precisely on the beat. Not so the LTA. While I would not describe its presentation as soulful in the manner of cajun cuisine, it has an unmistakable bounce to its step and there is a natural flow all of which contributes to the honesty of its musical presentation.

The Z40 is nearly unequaled at its price point. It lacks nothing, but it is not the final word on anything. But what is? I did have one nit to pick and that had to do with its ability to capture all of the most nuanced dimensions of harmonic interactions among the instruments and voices in an ensemble, orchestra or choir. Only very few of the very best systems can capture this most subtle feature of a musical presentation. It is a capacity to hear into the musical interplay between players and singers in a way that enables the listener to hear their influence on one another's playing and choices in the direction they take at any turn.

I've rarely heard systems capable of this sort of insight. I heard it to some extent on two of the systems I have had in my home: one built around Shindo horns and the 300B Ltd amplifier; once with the Soundlab 845 electrostatics; once with David Chesky's set up featuring heavily modified Quad 57s, a system that is otherwise compromised in terms of dynamic realism; and in fellow reviewer Robert May's system built around heavily modified everything including Cardas modified Magnepan 3As, Scott Frankland modified VTLs and more.

Hearing into the harmonic interactions has been in my experience so rare that on the few occasions I have done so I have left wondering whether I have simply made up the entire experience.

More To Review
I was first introduced to LTA by my friend, Jay Bargmann, who, at the time built his system around Spatial Audio driven by an LTA Ultralinear integrated. Sometime after I had formed most of my views about the Z40 I contacted Nicholas Tolson and Mark Schneider to ask if they had an extra Ultralinear on hand that they might be able to loan me for a while. They did and dispatched one to my home in short order.

My goal in listening to the Ultralinear was two -old. First, I wanted to see if the LTA way with the Berning circuitry extended further through their line-up: whether in other words what I was hearing in the Z40 was unique to it or distinctive of a more general LTA voicing. The second was to see if there were differences in the character of the two amps that were noticeable and that might suggest that LTA, like other amplifier and preamplifier houses were in the business of providing different flavors within a common voicing.

The ZOTL Ultralinear uses a commonly available and inexpensive TV sweep tube, the 17JN6, for power. Sweep tubes are rarely used in audio amplifiers. They are especially good for dealing with peak power requirements and are extremely linear in their performance. Since most tube amplifiers are transformer coupled, the 17JN6 tube is not widely implemented and I was able to find no extended discussion of their sonic signature (if any). The Ultralinear puts out roughly half the power output of Z40 and is thus characteristically mated with more efficient speakers.

Listening Via Ultralinear
I replaced the Z40 with the Ultralinear, sat back, and listened for an extended period over a few weeks. First things first. There were more overall similarities than differences between the integrateds. Both amplifiers mated well with the Solovox. Both were overall well balanced, revealing without being incisive or spotlit. Both were listener-friendly, involving, immediate, and informative. Both were almost hauntingly quiet.

The differences were quite apparent and in one respect surprising. The major difference was in the area of tonal balance. The Ultralinear was a bit whiter than the Z40, which presents a richer picture. The Z40 produces a more colorful and engaging sound. This had an odd initial impact on me. Given the speed of the speakers and the relative tonal whiteness of the Ultralinear's presentation, I sometimes felt that the music was speeding along right by me before it had a chance to be fully realized and before I could become fully engaged with it.

I made one change to the system at this point. I substituted Auditorium 23 speaker cable for the Anti-cable speaker cables that had worked so flawlessly with the Z40 and the Solovox. This single substitution had an outsized effect on the system's overall tonal balance. The sound became fuller and richer and the differences between the two integrated narrowed substantially.

Nevertheless, differences remained yet were of a different sort. Once I was able to get beyond the initial whiteness of the Ultralinear as a result of the cable change, I began to notice that the Ultralinear was capable of a degree of nuance and subtlety that was somewhat reminiscent of the Shindo Cortese when fitted with F2a power tubes instead of the 300B tubes it can otherwise employ. The F2a presentation is a bit less rich, weighty, and dense, but it is remarkably nuanced, subtle, and deferential which creates a kind of seductiveness that I found nearly impossible to resist. I found myself drawn to the Ultralinear in much the same way, or, I should say, for many of the same kinds of reasons. I would own a Cortese in a heartbeat if I could. I have no difficulty imagining settling in long term with the Ultralinear either.

The big surprise came when I switched speakers from the Solovox to the Magnepans. I began with the Maggie 1.7i. Because the Z40 is rated at somewhere between 40 and 50 watts, I thought it had a fighting chance to drive the Maggies. It did, but not convincingly. I could never get to the point of trying to analyze the particulars of the sonic landscape the combination created. The sound was not believable from the outset and I would not recommend such a pairing.

For reasons that now escape me, I decided to try the Maggie 1.7i with the Ultalinear whose 20 watts I was certain would be inadequate to feed the beast. Well, I was more wrong than right. At the end of the day, that combination would not make sense in a large room like mine, but in a smaller space (as measured by volume), it would make for a very seductive combination at low to moderate volumes.

The reason why is obvious – but only after the fact. Magnepan character can dominate an audio system. You don't get more out of a Maggie by adding more power or current (beyond a certain baseline). But you can get one of the things that stock Maggie aren't great at producing: and that is fine-grained detail and nuance. These are the signature features of the Ultralinear and to that extent they exerted a positive influence on the overall sound.

During the period in which I had both the Z40 and the Ultralinear in house a pair of Magnepans LRS arrived that I purchased so I can review different after market stands for both the LRS and the 1.7i. I broke the LRS in with my Pass Labs 250. The speaker had no trouble taking on all the PASS could give. Any thoughts I might have entertained about seeing how either or both LTA would make out with the LRS disappeared immediately.

Conclusions
LTA is a new name in audio, but with products like the Z40 and Ultralinear integrateds, it has every chance of becoming one of audio's venerable and long-lasting companies. LTA has taken a brilliant technical solution to a range of obstacles to executing transformer-less amplification in real-world circumstances and turned it into nearly equally brilliant performing audio components. They have not only breathed new life into transformer-less designs but have created some of the most musically persuasive and honest components I have had the pleasure of listening to.

The LTA website claims, and I quote: "Traditional tube amps are known for their liquidity and linearity, but their "warmth" masks details and can sound thick. Solid-state amplifiers give you that detail, but can be "clinical." ZOTL amplifiers give you the best of both worlds: beautiful tube tone with the clarity of solid-state(while being entirely tube-based)." Unsurprsingly, the website also references reviewers who assert that the Z40 "manages to tip-toe the line between a classic tube sound, and a modern, solid-state A/B amplifier".

To be sure, tube amps can be warm and solid-state amps can be detailed and clear. Tube amps can also sound thick and mask details. Good tube amps do nothing of the sort, however. And solid-state amps can also be quite dark and heavy, thus masking all manner of detail and shadings. But good solid-state amps do nothing of the sort.

I would have thought that these false dichotomies between solid-state and tube amps had already been dispelled many times over. If a solid-state amp is linear and tonally persuasive does that make it tube-like? If a tube amp is quiet and detailed does that make it solid-state-like? The good folks at LTA are no doubt looking for a niche – a way of describing or characterizing what they do that will ring true to both solid-state and tube fans. I understand, but in addition to giving oxygen to false dichotomies, they are selling themselves short.

LTA produces amplification for home use that pushes the boundaries of what transformer-less circuits are capable of. Their products deserve to be appreciated for their intrinsic qualities and not because they should appeal both to both tube and solid-state aficionados. They deserve to be appreciated in their own right by anyone looking to put together a home audio system that is true to the music, persuasively presents music of all types, hypes nothing while shining a positive light on it all. That's all the reason anyone who cares about music and its production through an audio system needs to realize that the Z40 integrated is special.

If you are putting a system together with the expectation that it will serve you well for a long time and across all kinds of music, then the Linear Tube Audio Z40 integrated amplifier is one of only a handful of amplifiers or integrated amplifiers you really must audition. So too is the Ultralinear. In the system, both helped to create a rich and engaging musical landscape. That presentation struck me a bit more refined but a bit less embodied. Different flavors within the same voicing. I could live happily with either – even more so with both! LTA is a company to keep your eyes on and your ears open to.

Specifications
Type: Vacuum tube stereo integrated amplifier
Frequency Response: 6Hz to 60kHz (+0/-0.5dB)
Power Output: 51 Watts @ 4 Ohms, 46 Watts @ 8 Ohms (0.5% THD)
Amplifier Class: Push-pull Class AB
Tube complement: Two 12AU7, two 12AX7, two 12AU7, and four KT77
Voltage Gain: 23dB (8 Ohm load)
Output Impedance: 1.2 Ohms
Input Impedance: 47kOhm
Hum And Noise: 94dB below full output (measured at 20Hz to 20kHz)
Inputs: Four stereo inputs via unbalanced RCA, and one stereo pair balanced XLR
Inputs: MM or MC
    MM Gain: 46dB fixed
    MC gain: 10dB / 20dB additional (56dB total or 66dB. selectable by jumpers)
    MM loading: 47kOhms
    MC loading: 10, 20, 30, 50, 100, 200, 470 Ohms
    selectable by dipswitch 100pf, 220pf, 330pf selectable by dipswitch
Speaker Output: Four WBT copper speaker binding posts
Headphone Outputs: Low: 220mW per channel @ 32 Ohms, High: 2.6 Watts per channel @ 32 Ohms
Tape Monitor: One stereo tape monitor out, and one stereo tape monitor in via Cardas RCA
Home Theater Function can select any input for fixed volume
Display: Sixteen levels of brightness and programmable seven second time out
Front Panel Controls: Seven brass touch switches (power, input, tape monitor, up, down, menu/select, back), volume control, and headphone speaker switch
Remote Control: All front panel functions using paired Apple TV Remote
Volume Control: 100 stepped attenuator (smallest step 1/1000th of total value) using Vishay Dale 1% precision resistors
Dimensions: 17" x 5.175 x 16" (WxDxH)
Weight: 18 lbs.
Finish: Aluminum case
Price: From $7650 on up depending on options

Company Information
Linear Tube Audio
7316 Carroll Ave.
Takoma Park, MD, 20912

Voice: (301) 448-1534
E-mail: hifi@lineartubeaudio.com
Website: LinearTubeAudio.com