n idea of reconciling two worlds of semiconductors and tubes, is perhaps an utopian one. Each of them is well-entrenched in their positions and is not willing to make any concessions. The situation resembles a religious dispute, because it involves mostly emotions and logical reasoning is treated with suspicion and usually rejected in advance as untrue.

However, if you keep an open mind, if you approach the topic without prejudice based on stereotypes, you might find it interesting that some solutions exists that allow one to take advantage of transistors where there is a need for high current and at the same time deliver performance similar to that of tube devices. In most such cases one benefits from qualities of both worlds while such solution involves only few, small compromises.

A company that knows how to do it is the Slovenian Audio Alto. The integrated amplifier we reviewed some time ago, the DMI 3 H, sounded as if on my Finite Elemente Pagode Edition rack there was a sophisticated SET amp, but in a small, slim casing. The monaural power amplifier, MSE 60's design is based on the said integrated but it is even more advanced, so expectations were really high before this test.

MSE 60

The secret of the integrated amplifier laid in the recourse to techniques that had been known for years, but which were rarely used, because of their limitations, which impose certain obligations on the user. Exactly the same solutions, but in a more elaborate version, one finds in the reviewed amplifiers.

Technology

MSE 60 is a monaural power amplifier (for a stereo system one needs two of these). The ‘M’ in its name indicates just that, while ‘SE’ stands for Single-Ended, a technology most often used in tube amplifiers, but not limited to them (more HERE). The idea is, that the signal is amplified in a single active element, without dividing it into two halves, as in the push-pull circuits. This is the most purist solution, but not a very effective one, ie. one needs to source a high power of electrical outlet, and only a small part of it is actually used to drive the loudspeakers. The rest is converted into heat and radiated into the air surrounding the device.

This means that the output power of such a compact device is limited. MSE 60 delivers 30W with a peak output of 2 x 60 W. I didn't say anything about output impedance because each amplifier is made to order for particular speakers (or rather their impedance) – I'll get back to that. The output stage here is a solid-state one – there are two MOSFETs here. They work a little differently than in a classic amplifier, because the output stage is actually a current buffer with a gain equal to 1.

Do you remember solid-state amplifiers by Italian company Audia Flight? I tested one (see HERE; in Polish) and Marek Dyba (see HERE http://highfidelity.pl/@main-2877&lang= ; in Polish) reviewed another and our observations overlap – these amps offer a remarkable approximation of tube-sound using transistors. Audio Alto follows similar path but added a twist to the story, ie. a tube input stage, which make sit similar in principle to products of the Canadian Tenor Audio. MSE 60 is thus a hybrid power amplifier, in which the actual amplification is realized by tubes and transistors are only used to provide current. There is no negative feedback.

Disadvantages of these solutions have been known for years: a relatively low output power and a very high temperature of a chassis, and on top of that a low damping factor. The latter here is higher than in tube amps with its value of 40, but it is an order of magnitude smaller than in conventional transistor amplifiers. Slightly higher is also distortion, usually corrected with negative feedback.

And last but not least, a thing that one sees in audio least likely: all amplifier stages are powered by regulated power supplies featuring FETs. Tubes' filaments in the driver stage are also DC regulated and stabilized. While this type of power supply for voltage section (that's what tubes are here) is not that unusual, a regulated power supply for output stage is rare. First of all, because this solution is expensive and difficult to execute properly. Well designed, however, it delivers surprisingly good results – it is not a coincident that new Naim 'DR' amplifiers, including the monumental Statement deliver such an astonishing performance – their output stages do feature regulated power supplies. To make the best use of such power supply, it is good to know, which impedance load the particular amplifier is supposed to work with. Audio Alto offers their amplifiers with stated impedance range they work best with.

Operation

That's it about technical side. As for aesthetics and make&finish all I need to say is this: these are creations of a perfectionist. The height of his devices is rather small, but the depth is impressive. The casings were made of aluminum elements, and the front panel is offered with few different finishes: titanium, chrome, or can be also made of wood. Amplifier features two RCA inputs. One of them is a “classic” one to be used with a preamplifier (brand's lineup includes the PSE 10 preamplifier). The other one is a 'direct-in' input with signal being delivered directly to the output stage. One can use “LOUDSPEAKER OUTPUTS” of one's amplifier, for example a tube one. In this case sound signature of this tube amplifier should be unchanged, but the Audio Alto amplifier will deliver more current to better drive chosen loudspeakers.

There are two switches on the front - Power and ECO. The latter reduces the output power by 2/3 (so it is limited to 10W), and thus power consumption. This reduces the consumption of energy, as you should know that the Class A amplifier, regardless of whether we play the music or not, it always works at its maximum power consumption. If you do not use the device, and do not want to turn it off completely or maybe prefer to listen to the music quietly, then the ECO mode certainly might come in handy.

The Audio Alto monaural amplifiers were placed on the top shelf of Finite Elemente Pagode Edition rack, one on the top of the other. Perhaps it would be better if they stood side by side, but unfortunately I did not have much space. They drove Harbeth M40.1 loudspeakers and the signal was sent to them from the Ayon Audio Spheris III preamplifier. The source was the two-box Metronome Technologies Kalista CD Player (2016). Amplifiers are delivered with power cables produced by the AA, equipped with a very nice plugs similar to WattGate's, with gold contacts and I used them for this test. The signal from the preamplifier was supplied via Acoustic Revive RCA 1.5 TRIPLE-C-FM interconnect, a I also used SPC-2.5 TRIPLE C-FM speaker cable by the same brand.

The amplifiers by Saša Burian performed extremely well and turned out to be a perfect fit into both, my reference system, and my expectations towards any high-end devices. On a surface, these devices seemed completely different from Soulution 710, which was replaced during the test, they filled that gap in a very competent manner. They delivered a different set of features, but with a common “core quality” with Soulution: a fantastic differentiation.

Although it is difficult to describe with one sentence a characteristics of these monoblocks, Grzegorz of Nautilus while picking up the Ayon HA-3 after the test sat down for a moment, listened to Slovenian amps and just said, "serenity and power." Although these are only couple of many qualities building up this performance, they are surely among the most impressive ones.

We are dealing here with a sound resembling, and in a very suggestive way, what one gets with a sophisticated Class A SET amplifier. But one of those really sophisticated ones, ie. those that deliver what many describe as a “warm” sound which is an intended result of the design but that comes not from “tuning” the tonal balance, softening the attack, or anything like that, but from the wealth of information "building up" a natural sound, that we perceive as "warm"- rich, saturated, relaxing and smooth.

That's how these amps sound like - unusually smoothly and nicely. But this is not another "nice" sounding product imitating tube amplifiers, it is absolutely not! These Slovenian devices are so incredibly fast, they have so fantastically shaped tone that one immediately forgets about all those “colored” competitive products. Although their sound might actually seem soft and delicate, in fact, it is extremely fast. That's also how my Harbeth M40.1 loudspeakers sound like, they are quasi-warm, but also tend to surprise all those who visit me with impressive dynamics, and my Soulution amp is yet another example of this type of performance. That's why I really appreciate both this components of my system.

Both are extremely resolving, that should be clear. This is not the top-high-end level yet, but considering the price of MSE 60, I have to strongly emphasize that the resolution is way above average, because one doesn't find something like this for the money, and more money, even much more, will buy you only small improvement in this regard. What are the benefits of this quality? First of all, a perfect "compatibility" between the recordings that do not belong to the best there are and those that in my opinion are masterpieces of the best sound and mastering engineers.

You can surely remember that I already mentioned an outstanding differentiation, right? In any case, I would like to remind you of it, as the reviewed amplifiers do not unify presentation, each album type is presented in an accurate manner. Yet ALL discs sound “competently” and "professionally". Let me explain this with two examples: the V by Maroon5 and a CD-R copy made of the master of Rosemary Clooney Sings Ballads prepared for the "Stereo Sound" magazine.

Saša's amplifiers listened only for a short time, or in a not properly set up system, may not remind you a typical "tube sound". They are open, fast and very precise in building a sound image. They will disappoint those who knowing that this are class A, single-ended with no negative feedback amps with not so high damping factor, would expect slow, warm sound. If that was the case it would be better to immediately look for something else. Alto Audio play so quickly that there is no time for any blurring of the attack. Therefore, one can appreciate the immediacy of the sound on Clooney's album. Everything was beautifully shown, dynamic, highly transparent, yet coherent. With such very good quality recordings the tested amplifiers "open up", present as much information as the source is able to deliver.

And now: devices that sound so good with high quality recordings usually tend to “massacre” those of lesser quality, meaning about 99.9% of all recordings. To make thing easy they accurately show the attack of the sound and details, trying to convey them as faithfully as possible. However, there is a class of products, the high price range, which does something more. AA with a compressed signal such as that of Maroon5's recording sounded like good, powerful tube amplifiers because they extracted intentions of the sound engineers and producers of the recording, they eased attack, but did not turn the presentation into a soft, warm “pulp”. It was still an accurate, precise performance, but with something "more", which eased the problems that hid all this precision under timbre, liquidity, simply - the melody.

I perceived a reproduction of both range extremes in a very similar way. These amplifiers do not emphasize them, but if the recording included more bass, it is shown in a powerful way. Only that in most cases there is still not so much happening in the lower region area. But even then the differentiation of bass', bass guitar's, etc., tone was really nice with AA. And even if it seemed that the lower part of the range is rather delicate, there were still large phantom images and large scale of a sound as a whole. And this, in turn, proved, that the low frequencies harmonics built something more than I thought, that there was something more there, just like in the real world, like at a concert.

And that's how I perceive these amps, as a window opened to the music. If you listen to a studio recording with a “strong” production (ie. compressed, multitrack recording, with a lot of manipulation), the AA will take it all in and merge into something, you will be happy to listen to. On the other hand, when you listen to high quality recordings of a realistic sound, the amplifiers will suddenly open to multiple possibilities and interpretations, letting you into the deeper layers of the recording, not trying to fix anything in it.

This, of course, is not a perfect device, because there is no such thing in audio. One of its "disadvantages" is a low output. This is obviously not a disadvantage by itself, but a limitation one needs to remember about. Tube amplifiers with similar power output will play subjectively louder as they will get gently into overdrive. AA are ultra-precise and if they start to overdrive, one can immediately hear that. But it can happen above all with purist realizations with a real-live-like dynamics. With rock and pop music it will be much much less pronounced. And if you pair them with loudspeakers with a higher than average efficiency and friendly impedance curve, you won't hear that at all.

The tested amplifiers do not build deep soundstage. They prefer the first plan, spread the stage beautifully at the sides, remarkably deliver sounds out of phase, ie. they surround listener with sounds that are so encoded in the recording. Events on the stage are, however, focused on the line connecting the speakers, that's where listener “sees” all that's happening. Without voices popping-up from the mix, without emphasizing instruments, ultimately they offer a totally different (much higher) performance quality than that. Yet all the time we know that what is happening in front of us is the most important part of the presentation.

Summary

These are remarkable devices. Built with passion, but also with proper engineering reliability by a man who knows what a good sound is. These amplifiers sound like a high quality SET, but with better bass control and better balance. Only the most expensive amplifiers based on triodes, such as 2A3 (in Polish), 300B, 211 and 845 show even deeper layers of internal relations inside music, a “tissue” applied to the structure of the sound. But even in such company, much more affordable, MSE 60 monaural amplifiers prove their class. If you just do not have too big room, or difficult to drive loudspeakers, you can buy them right away and I'm sure you will not regret it.

The MSE 60 amplifiers feature a form of long, solid "drawers". Their mechanical construction has been optimized in such a way as to ensure maximum rigidity to the whole structure and so that the whole body works as a heat sink. The electronics have been suspended from the top wall, that together with the front and rear form a sort of "spine" of the whole design. The bottom is an aluminum plate.

Front and back

On the front there are two buttons and four LEDs. One of the buttons allows user to activate the device - the red LED will change color to the blue. The activation takes approx. 45 seconds, when various voltages are served and parameters stabilized. This extends the life of the components significantly, mainly the tubes. The second button is used to switch the device to the ECO mode – the blue LED will change color to green ... of course. This button reduces the output power by 2/3. On the back there are two RCA inputs - Hi and Lo, a single pair of speaker connectors (on request you can add a second pair), IEC socket with a mechanical switch and a trigger socket. I should mention about the switch, which can cut off the protective/ground conductor in the power cord which might come handy if there us a problem with a ground loop resulting in a hum coming from the speakers.

Inside

Unscrewing the casing shows that it is even more complex than it would seem based on external inspection. A steel chassis is bolted to an aluminum frame, and there is also a second one, shielding, among others, a large toroidal transformer. On the sides one finds medium-sized radiators. FET power supply is fixed to one of them, and a powerful rectifier and two IRFP150 power transistors to the other. Near the front panel one finds two PCBs with logic circuits and a separated power supply for them.

There are only highest quality passive components – one can find everywhere small and big (10 uF) WIMA polypropylene capacitors, as well as two banks of Nichicon Muse electrolytic capacitors. It turns out that the input tube is a double triode 12BH7AEH by Electro-Harmonix. The circuit looks fairly simple, as it usually is with tube amplifiers. Except, of course, is not this type of amplifier, thus simplifying the circuit required a lot of work. Let me add that designer decided to use a high quality power line filter, placed just behind the IEC socket.

Clean, precise work.

Specifications (according to manufacturer):

Input sensitivity/impedance: 1V / 100 kΩ
Gain: 23dB / 0dB (selectable)
Noise: - 95dB
Output impedance: 0.2Ω
Damping factor: 40
Output power: 35W / 4Ω or 6Ω (selectable)
Frequency range: 5-60 000 Hz / -1dB
Dimensions (W x D x H): 295 x 465 x 90mm
Weight: 13kg