AudioPax l50 Preamplifier and m50 Power Amplifier

This is one of those tests I've been wanting to do for a few years; but it kept being postponed and at one stage it seemed like it would never happen. In the meantime ownership of the company changed, the Model 88 I was originally planning to test has been eclipsed by the Maggiore ("reference") line M50, though the Model 88 remains in the Audiopax portfolio within their "Classic" range. In fact I had started inquiring with the Brazilian company Audiopax already back in 2011.

Brazil is surely not known for being a home to many audio companies. But it was there, at the beginning of this millennium, where one of the most interesting tube amplifier manufacturers was founded. A manufacturer which is particularly interesting I might add, as they have their own concept of how a tube amplifier should be designed in terms of both sound and aesthetics. In this regard Audiopax reminds me of another, equally exotic audio manufacturer from South Africa, Vivid Audio, who offers loudspeakers taking the concept of Bowers & Wilkins Nautilus speakers even further than the original manufacturer.

Mr Eduardo de Lima, founder of Audiopax, was an electrical engineer who started his audio adventures in 1997 with his first commercial product the SE310 amplifier, a 300B SET, that was presented together with CX305 loudspeakers during VSAC Show in Silverdale, USA. In that same year he also developed the LM3 (Low Mu Triode with Higher Raw Efficiency Emulator - LMTHREE), that emulated the behaviour of 300B tubes using KT88 valves. This emulator was used for his next model, SE388, which was presented in 1998 at the Sao Paulo Hi-Fi Show and VSAC Show.

The big step for AUDIOPAX came in 2001 with the launch of the Model 88 that for years was the best known Audiopax model. It premiered at CES in 2002. Each of these mono amplifiers featured two KT88 tubes in the output stage. And yet they did not work in push-pull configuration. But it wasn't a classic Parallel Single Ended configuration either.

Mr Eduardo de Lima's objective was to create an amplifier that would use some popular (thus not expensive) tubes, would work in Class A Single Ended configuration, would offer reasonable power output and yet sound like a low-power SET amp such as those built around triodes such as: 300B, 2A3 and 45. This technology was called Perfect Triode Simulation (PTS). Prototypes were based on KT66, that were later replaced with KT88. For this amplifier Audiopax incorporated another of its developments which Mr de Lima named Timbre Lock. Simply put, this can be described as a feature that allows the most appropriate interface between the different components in the audio chain. It replaced LM3 emulator solution.

Timbre Lock

Mr de Lima's approach was to exploit the qualities of the tubes he worked with rather than fight against them. Each Model 88 mono amplifier consisted of two independent amplifiers within its chassis — the solution was called ASTAT (Asymmetrical Series-Twin Amplifier Topology). Each amplifier featured independent bias/Timbre lock adjustment for its tubes. With these adjustments the user could change the working conditions for the tubes and by doing so, change the sound. This is quite different from the approach that an amplifier should be just like "a piece of wire amplifying the signal". This design acknowledges that an amplifier is an imperfect tool; but it also shows that these imperfections could be used to the user's advantage.

The basic idea was to manipulate the KT88 characteristics in such a way that it would be identical to that of a triode tube such as a 300B; but offering bigger gain at lower cost. In a 2002 interview given by Mr de Lima to Srajan Ebaen, Mr de Lima stated: "one the big challenges was building a very low noise power supply—it was necessary to achieve the ultimate goal (you can find the interview HERE). It is relatively easy to lower the noise by using feedback. But Audiopax amps use no feedback at all, which required the designer to develop a different solution. In 2003 Audiopax started to work with Avantgarde Acoustic USA. The Avantgarde horn speakers feature sensitivity as high as 103 dB (or more); so for these amps to work really well with those speakers, noise levels had to be kept extremely low.

Maggiore l50

In 2004 Audiopax released their Model 5 preamplifier using Timbre Lock. Then in 2011 a completely new line called Maggiore was introduced. Unfortunately a year later Mr Eduardo de Lima passed away and soon after that the second partner in the firm died too. The last partner, the youngest one, Mr Silvio Pereira, became the only surviving partner. At the time he was a technical director working for Global, the biggest Brazilian TV network. He was doing very well there and happy with his job.

The next few years were very hard for Audiopax. After Mr de Lima's passing orders stopped coming as customers were unsure about the company's future. Finally Silvio and his wife made a difficult, yet very important decision—they decided that Audiopax was to become their full time job. It was not about the money because, as Silvio told me, working for Global he earned much more. The reason was on the one hand his passion for music and on the other he couldn't let Mr de Lima's legacy to die with him.

As it quickly turned out good people attract other good people, so very soon they had great professionals working for them. They all decided to take up the challenge of continuing development of the new amplifier that had already been initiated by Mr de Lima himself — Maggiore. These amps also use KT88s, the design is similar to the Model 88, but a third tube, indeed a third amplifier was added. They also developed a new chassis—the initial Maggiore amplifier the M100 had a rather 'industrial-style', the new one can still be called "macho", but it is definitely more stylish than its predecessor.

The key feature of the new amplifier is still Timbre Lock. Silvio told me that it's not really about adjusting bias (within 78-92 mA range), but about how it effects the transformer's loading. The latter sports independent, asymmetrical windings for each amplifier. The idea is to have 90% of penthode efficiency while preserving the gain curve of a triode.

The matching preamplifier from the Maggiore line is called l50. One might think of Audiopax as a tube company, but in fact that's not the case, as this preamplifier proves by using MOSFET transistors instead of tubes, albeit in a very similar layout (as the power amplifiers). It also features Timbre Lock. The transistors are working though with high voltage current, and are treated as if they were tubes.

SETUP

This test was only possible thanks to Mr Geoff Armstrong's help, who is the European Audiopax distributor. His headquarters are situated in Monaco, and he specializes in finding exotic brands that offer something unique. His portfolio, apart from Audiopax, includes also Polish brands such as Ancient Audio and LampizatOr.

It was not a typical test as the time for the listening session was extremely limited. Geoff and Silvio visited me right after the Vienna Show. We brought boxes in, unpacked them and Silvio started to do his magic. Three Timbre Lock knobs allow the user to significantly change the sonic characteristics. Performance might be more "krell-like", or more "tube-like". The changes are more complex than that but that gives you a general idea. For facilitating these adjustments we used a cello recording—I offered a few and Silvio chose Bach's Cello suites Nos 1,3&5 played by Mischa Maisky.

We placed the amps on the floor on Acoustic Revive RST-38H platforms and hooked them up using Acrolink Mexcel 7N-PC9500 power chords. The preamplifier landed on a shelf of my Finite Elemente Pagode Edition rack and was using Tellurium Q Silver Diamond power cable. The RCA interconnect connecting it with power amplifiers came from the same Tellurium Q line. As a source we used my Ancient Audio AIR V-edition CD Player connected to the preamplifier with RCA Siltech Triple Crown.

Two hours later I was ready for my listening session.

SOUND

Recordings used for the test (a selection):

Artur Lisiecki Acoustic Harmony, Stone & Ashes, Fonografika 559040, master-tape copy, CD-R (2010); review HERE.
Artur Rubinstein, Artur Rubinstein plays Chopin, Polskie Nagrania MUZA/Polskie Nagrania PNCD 487, CD (1984/2008).
Billie Holiday, Jazz at the Philharmonic, Clef Records/UMG Recordings UCCV-9476, "David Stone Martin 10 inch Collector's Selection", SHM-CD (1945 | 1946/2013).
J.S. Bach, Cello suites Nos 1,3&5, perf. Mischa Maisky, Deutsche Grammophon/Universal Music LC (Japan) UCCG-50085, "Best 100", SHM-CD (1999/2011).
Laurie Anderson, Homeland, Nonesuch 524055-2, CD + DVD (2010); review HERE
Mark Hollis, Mark Hollis, Polydor 537 688-2, CD (1988).
Mendelssohn & Brahms, Violin Concerto, viol. Hilary Hahn, "Best Classics 100", Sony Classical/Sony Music Japan, SICC 30088, Blu-spec CD2 (1997/2012).
Nat King Cole, The Christmas Song, Capitol/Audio Fidelity AFZ 225, "No. 0115", SACD/CD (1967/2015)
Stan Levey, "Grand Stan", Bethlehem/Toshiba-EMI TOCJ-62028, CD (1957/1999)
Tom Yorke, Tomorrow's Modern Boxes, Hostess | LANDGRAB RAB001J, CD (2015).
Wes Montgomery & Wynton Kelly Trio, Smokin' At The Half Note, Verve 2103476, "Verve Master Edition", CD (1965/2005).
Wes Montgomery, Full House, Riverside/Universal Music (Japan) UCCO-9207, "Jazz The Best | Legendary 100 | No 7", CD (1962/2008)

Before I began I thought that it would be an easy one—the very short time for getting to know this set would let me just touch the topic without getting in too deep, just describe my initial impressions. Right after I started critical listening I knew that this was such a refined, fantastic performance that the review had to be very serious. A much shorter than usual listening session had to be enough; but I still tried to listen to as many albums and tunes that I could before Silvio and Geoffrey packed the devices and drove back to Monaco.

On the other hand maybe it was for the best, the short listening session I mean. This Timbre Lock feature, the key to the sound of Audiopax products, is simply addictive. Despite the fact that, in theory, there was only one 'correct' setting, I couldn't help myself and experimented with it while listening to the first few albums only to get back to the settings Silvio initially chose using the recording of cello played by Mischa Maisky—it was simply the best one.

Regardless of chosen Timbre Lock settings the system had its own sonic characteristics that I could describe and assess. It might seem that this solution allows for actual change of fundamental sound characteristics; but it's not quite that simple. It's not as though using the knobs one could set the amps to sound like Krell, VTL or Kondo. It's always going to be an Audiopax amp. The real purpose of Timbre Lock is to allow the system to perform at its best. And within this type of sound one could find similarities to sonic characteristic of other brands of amps. And still — similarity concerns rather a certain design type and not its particular embodiment.

Performance of this set reminded me of that of the Naim Statement. Some differences were obvious; but so were the similarities. It was an amazingly refined sound of similar class as Naim's but also Einstein's and Ayon's (Spheris III + Crossfire Evo). Similarities in terms of richness of the sound, tangibility, large, three dimensional phantom images and fantastic resolution.

The latter is simply remarkable—Audiopax delivered even more resolving sound than my own, reference system, which so far happened only once with the aforementioned mentioned Naim Statement. I mean 'real' resolution and not just the, often mistaken for it, highly detailed and selective sound. It is a resolving and yet warm sound. Without even as much as a hint of artificial 'warmth', as this amp delivers particularly linear performance, and yet the sound is warm.

We agreed about this with Silvio, an expert on picture quality—that one should compare the image quality of LCD or even plasma 4K TV sets, with the resolution of an image provided by a 4K DLP or even better—with a film. The former would impress with an incredibly detailed image. Compared to them the image one can see in movies at the cinema seems very smooth, as though it lacks details. But does it? Of course not—this smoothness is the result of millions of details that combined, offer an added value. When details are very distinct they tend to destroy the illusion of the image or the sound in our case.

The system consisting of the l50 and m50 monoblocks does exactly the opposite—it unites elements rather than separates them. Don't get me wrong—differentiation of every aspect is fantastic. This might have directed my choices towards live albums. To be honest I'm not particularly fond of 'live' albums. Since I go to many concerts I can clearly see a difference between what I can hear live and what live recordings have to offer. It is easier for me to accept some artistic concept created in a studio.

Studio recordings in this system sounded very coherent. Even when I listened to electronic music, such as Tom York's album, with something 'new' he created, something I could not compare to 'live' sound. The frequency range was nicely extended, including the lower end, and all parts of the range combined into a coherent whole. It seemed that there was a slight emphasis in the lower midrange and I think that there actually was, as the other systems I mentioned before had given me exactly the same impression. But it is just a gentle touch—nothing that would bother the listener.

But when I played Full House, Wes Montgomery's concert recorded in Tsubo Club, or Mark Hollins solo album I had to admit to myself—as I wasn't ready just yet to say it out loud—that in terms of tangibility of the sound, its naturalness, its 'normality', this Brazilian system offered something absolutely extraordinary. It perfectly conveys even the smallest changes in instruments' placement on the stage, it creates an amazing space, also around the listener, if that was the producer's idea, instrumental separation is also fabulous and yet they come together to create a wonderful musical spectacle. I think that it is one of the advantages of mono (monoblock) amplifiers—they are able to recreate this amazing ambiance of many recordings.

With a more analytic approach I'd have to admit the leading edge seems slightly round. But even if it is so, it simply doesn't matter. Because this type of presentation will remind everybody of what they know from real life—many elements that together create something dense, rich, and it's the sum of those elements that finally arrives at our ears.

Lower bass is tuneful, well differentiated and energetic. Top quality, powerful solid-state amplifiers such as Naim Statement and Soulution 710 are able to deliver even lower and faster bass and equally tuneful They might be solid-state amplifiers but they don't sound like a 'stereotypical' transistors. They deliver the 'right' sound—slightly soft but energetic and internally focused.

The extreme of the range is simply put: perfect. Not as 'soft' as delivered by SET amps such as, for example, Phasemation M-1000; but instead, capable of differentiating recordings in an even better way. There is no brightness, no harshness—this doesn't happen at the top-high-end level.

Summary

One of the tests any audio product has to pass to attract my attention is playing some old recordings. I mean older than me, and maybe even older than my parents. Such as bonus tracks on an album of Rubinstein's recital, or Sinatra from 1930's and 1940's. Audiopax delivered rich, deep performance with them, not trying to make them something they were not. They sounded right, as I imagined they should have.

The system played recently recorded albums in a similar way, giving them something 'behind' the sound that made the presentation fluid, effortless, energetic. It's an amazingly immersive performance that I loved to dive into.

DESIGN

l50 preamplifier

The l50 preamplifier is a two-box device. The larger chassis holds a gain stage and choke, the other is a power supply. Both are made of aluminum plates bolted together, anodized for the black color. Both fronts feature a stainless steel element with the brand's logo. The product's name is nowhere to be found on the chassis.

Front panel sports five polished steel knobs. Each knob features a 'collar' with a proper scale on it. The first two knobs allow adjustment of Timbre Lock for the left and right channels. In the middle sits the volume control and the next two work as input selector and standby switch. To turn the device completely off one has to use an on/off switch on the separate power supply.

The rear panel sports high quality Neutrik connectors. There are five RCA inputs. One of them is a "bypass" that allows integration of this preamplifier with a home theater system. One of the inputs features both, RCA and XLR sockets. There are three outputs—two RCA and one XLR. Even though the XLR output might suggest it, the preamplifier is not a balanced design—input signal is symmetrized and before output it is de-symmetrized using high quality transformers. The connectors' descriptions are engraved directly in the metal panel. There are also two Neutrik made multi-pin sockets used to connect the device with power supply using two long cables. One of them is a power cable, the other delivers the signal from remote control receiver. Volume control is realized using a black Alps.

The remote control is of RF (radio) type which increased its range. The rear panel of the power supply chassis sports an antenna socket (that looks like a wi-fi one), two multi-pin sockets to connect PS with main device and and IEC socket. Also there is a ground switch. One finds two switches on the rear panel—one changes the gain setting, the other selects whether the RCA or XLR sockets of the CD input is active.

The whole electronic circuit sits on four PCBs. One of them hosts inputs, matching transformers and input selector relays. All audio paths go through one circuit stage that uses a single Mosfet active device working entirely without feedback. The controlled polarization of this device is the key to its performance. Starting with two independent 240VDC power supplies (very unusual for a solid state preamplifier) passing through a circuit that controls the distortion spectrum and is capable of greatly reducing, or even eliminating, the characteristic distortion inherent in loudspeaker drivers. Another innovation present in the Maggiore L50 is the use of inductive load which, due to the instantaneous current capacity obtained in this configuration (doubles the traditional resistive load), resulting in visceral dynamics.

Audiopax_Maggiore_m50_REVIEW (7)

m50 mono amplifiers

These Brazilian amplifiers feature vertical design. Just like top Mark Levinson amps, these also are build in layers. There is a steel frame with aluminum plates bolted to it. The top cover is made of polished, stainless steel. This is where three EAT KT88 power tubes sit accompanied by three drivers—CV4024. Tubes work in single ended configuration in class A. Drivers are placed very close to the inputs. Input tubes deliver high gain (x35) and output tubes work mostly as current amplifiers.

In the front there are three knobs that allow to adjust Timbre Lock. Each knob has a transparent cup with green, orange and red LEDs under it. Behind the knobs there is a Timbre Lock switch, and on/off switch.

Inputs, RCA, and XLR, are placed on the rear panel The latter is followed with de-symmetrized transformer. There is also a toggle switch that allows the user to chose between these inputs. Each amplifier sports single, gold-plated speakers posts. Below there is an IEC socket and a multi-pin socket marked as "synchronicity" that allows to synchronize switching on and off of both monoblocks. The Amplifiers sit on small feet fixed to the wooden base. Make and finish are really good.

A PCB with the amplifier's circuit is fixed to the upper panel It features the same capacitors as used for the preamplifier, and high quality resistors in the input section. There are also three large filtering capacitors. Power supply section sits on a separate board fixed to the bottom panel next to a large toroidal power transformer.

Preamplifier + power amplifier

AudioPax

MAGGIORE l50 + m50 (x 2)

AUDIOPAX SISTEMAS ELETROACUSTICO

Price (when reviewed):