Translations: Krzysztof Kalinkowski

I wanted to test the amplifiers of the Czech company KR Audio for a long time, but there was always something in the way. I heard them many times during presentations and shows, and I made a dozen talks with Eunice Kron (interview HERE), but the happy finale was far away. But fortunately, a new distributor on the audiophile scene, the Warsaw based SoundClub helped me make this dream come true. We received for testing the integrated amplifier Kronzilla SXI-S in the version with separable preamplifier and power amplifier. This is an incredibly heavy piece of engineering (50kg) with mighty, really big, T-1610 tubes in the role of the power amplifier. It would be best to say, that this is a hybrid amplifier, because semiconductors are used to drive those monsters. This is the opposite of what we are used to, because if, then the tubes drive the transistors. I would also like to remind, that we have already dealt with this concept in “High Fidelity” before, in the form of a splendid amplifier AI-45 MkII from the Polish company Linear Audio Research (test HERE). And the effect was very good. Anyway, the first thing we notice – after our broken back – when we put it on the shelf, and this does not crumble under the weight, are the tubes. I saw them many times before, but only now, when the amplifier reached my home, I could fully appreciate the effort put in the design and production. Once seen, they will be the benchmark of that, what is possible in the tube world, and that for a long time…

They are huge. Such sizes of tubes exist in the nature, they do, but they were reserved only for older circuits, where they worked as emitter tubes in high power transmitters and in radar equipment of the former USSR. But they are almost non existent in audio, because the adaptation of them to process audio signal is quite problematic. KR Audio approached the problem globally – when there is need then there needs to be a solution – so a new tube was born. The triode T-1610. Interesting enough, this is a directly heated triode – on the bottom, below the gold plated brass base we have three pins for the amplifying elements (anode, cathode and mesh) and one pin (and the pins have the size of an AAA battery) for the heater (5V, 3.8A). This is very similar to the 300B triode. And I call upon this similarity not by coincidence. If we look upon the world audio market, then we will see that there are big amplifying tubes, the triodes 211 and 845. Used in the most expensive products those allow having big power from a SET setting. I know that many users of those amplifiers are absolutely satisfied and value the speed, dynamics, and even the strong white light they emit. Please do not take it personal, this is only my opinion, but no amplifier on those tubes ever “touched me”, my heart. Their sound was always too analytic, too clinical. Probably I am wrong, and there are amplifiers with such tubes that sound warm and nice, but the best, real hi-end amplifiers I heard, were based on the 300B. I’m not a dogmatic, it does not matter to me what amplifies the signal, as long as it is done right, but the previous experience distanced me from the 211 and the 845. This is why, although I wanted so much to hear the Kronzilla, I was afraid this tendency would be repeated, or even amplified – in the end this is the largest tube I ever heard in my life.

Regardless of how it turned out, I’ll just say, that the Kronzilla SXI-S is an integrated amplifier, with a passive preamplifier and with the input and control sections based on FET transistors working in class A, while the power stage is based on power triodes T-1610 manufactured by KR Audio in Czech Republic. The whole amplifier is built there. And the tubes were quite exploited; we can expect 50W at maximum distortion of 3%. The tested amplifier has a power stage inputs and preamplifier output, what increases the price of the amplifier by 1000zl.


The sound of the Czech amplifier has two characteristics that were never present at my home before in such a refined form: the midrange and treble timbre and a natural sound stage. This is an important information for me, as the system used by me, composed of the preamplifier RS-28CX Leben and the power amplifier M-800A Luxman is outstanding in this aspect and, for the given money, gives a sound level difficult to reach in another way. Only a few times I could witness a listening session that would clearly, without searching for the fine details, from the very beginning, have a better “package” of assets than my amplification. But I heard that. For the first time, since the system Krell EVO 222 + EVO 402 I found something in the sound of the tested amplifier, that moved me so much, that I modified the expectations against my home system. I mean – raised them. This is symptomatic, that in the context of the Kronzilla, the ultra-purist, class A, SET amplifier I call upon the Krell system – a fully solid state, a synonym of the semiconductor hi-end. And regardless how unfitting for many the combination of words “hi-end” and “transistor” might be, I dealt with something like that. The thing I heard with the Krell, and stayed with me for long, was the bass – brilliantly controlled, perfectly led, just like the one, I heard probably once in my life, during the Ancient Audio Wing project (report HERE). The rest of the aspects of the sound were also outstanding, but this element, together with the incredibly drawn space, allowed me to look differently at the transistor. The Kronzilla gave me the same amount of pleasure, but on the other sound of the spectrum – from the side of the treble and midrange. I do not want to sound dogmatic – I am far from putting the case ideologically – and this is not the final voice in the discussion ‘solid state versus tube’, but there is something in it. So is this a pure wonder, light without a trace of shadow? No. That’s it. You must pay for everything. And in this case, every zloty spent on this amplifier, under the condition that we accept its limits, will repay hundredfold.

I started the description from two elements: timbre and space, because those are the “locomotives” here. The way the view is being drawn, information about tones, halftones, half-shadows or shades is exceptional here. Regardless of the technology we deal here with. This is hi-end in pure form. The voices of vocalists: Duke Ellington from the disc Louis Armstrong & Duke Ellington The Great Summit – The Master Takes (Roulette Jazz/EMI, 24547, 2xCD) and Carmen McRea (Carmen McRae&Juliet Lewis, Bethlehem/JVC, VICJ-61458, k2 HD, CD), saxophones: Sonny Rollins’ from Way Out West (Contemporary Records/JVC, XRCD), trumpets: Miles Davis’ from The Complete Birth Of The Cool (Capitol/EMI, 94550, CD), and above all the piano: from the disc Pasodoble Lars Danielssona & Leszek Możdżer (ACT, 9458-2, CD; review HERE) and Bill Evans from the disc Bill Evans & Jim Hall Intermodulation (Verve/Universal Music Japan, UCCV-9342, CD) – meaning that everything that operates in the midrange and above it – had a “magical” timbre. Full, saturated, rich in small nuances, etc. And this is not about any tricks, “magic” like in a circus or fare. There it is about deceiving the audience, manipulating him to have a few moments of fun. This is what we expect going to the circus, don’t we? The magic of the Kronzilla is from another tale. Definitely. This is “full time” magic, where when somebody casts a spell then this is not for a moment, this is real and permanent. Like with this amplifier. I called upon so many discs at once, because I wanted to tell, that the Czech amplifier keeps its assets in a broad repertoire and time spectrum. I add Zoolook J.M. Jarre (Dreyfus/Sony Music, EPC 488140 2, CD) and the single World in My Eyes Depeche Mode (Mute, CD Bong 20 SP CD) and we are still talking about the same thing. The timbre of the midrange and most of the treble is dense, full and smooth. The upper treble is also smooth, but also a bit rounded. This is incredible, but it does not interfere with anything. And both elements are connected to a breathtaking sound stage.

The latter is not especially deep, or extraordinarily broad, this is not about amazing with size (sorry to all gentlemen…), but about organizing the space of the stage, the positioning happens from itself. This is one of the most natural sound stages I ever heard. Please note that I am not talking about ‘most precise’ or ‘most thorough’ stage, because this is not what it is about in the Kronzilla. The last descriptors come directly from the test of the Krell. We will have to wait until the top hi-end to see the combining those two characteristics, and this amplifier is not the most expensive one on the market. Anyway the sound stage is incredibly vivid and spacious in a very natural way. I never heard at home the events being drawn in this way (because this is not only about the instruments and more on this later). Instantly all jazz discs from the 50. and 60. got breath and credibility. If I would only listen to that kind of music then I would put the Czech amplifier on the pedestal and pray to it every night looking at the lit tubes… And it is about credibility. Listening to subsequent discs it was so, that our brain (or at least my brain) did not have to work as hard as with other devices. And I am not thinking about brightness, but about the fact, that we get here the full information, already tidied up, not needing any fitting together of any loose elements. It is often so, that while many systems seem to be good, they are fatiguing in the end. With the Kronzilla we will never get tired. There is nothing to calculate with it, nothing to clean up. We get everything presented on a silver plate.

Like I mentioned, this amplifier is on the opposite part of the spectrum to the Krell. My system is somewhere in the middle. Those are the same quality levels, but how different is the sound! Listening to those three systems in a row we can see what is possible and finally end the pointless and harmful valuing of the devices based on their construction. There is need to differentiate between the “good” and the “bad”, but if the case is clear, and we know that we deal with something “good”, we should avoid hasty decisions, because we do harm to us or to other people. Listening to the Kronzilla with the Harpi Acoustics Dobermann, that reside with me as reference loudspeakers; I forgot for some time, that I had any complaints about them with regard to the upper midrange. Because I know where to look for, still, somewhere on the bottom I heard the slight upping of the frequency range there. But the sound was superb – fluent, smooth, like never before. If you remember our discussions regarding what is the truth in audio (for example during the KSS meeting about K2 HD discs – coverage HERE), or the lead article from July (can be obtained in PDF HERE), then you will probably know, that in my opinion the system should be maximally transparent and should not create anything by itself. I prefer more thorough, and thus more truthful, because, in my opinion, the creation of that what we hear should start with the recording and mastering. Audiophilism is a way to reproduce as thorough as we can what is on the disc… Regardless of the way we look at it, the Kronzilla forced another dilemma upon me: is it better to play with a tube like this and the Dobermann or differently – with my system composed of the Leben with the Luxman and the Sound&Line speakers I mentioned in the lead article. And I do not have a clear answer to this question. Until recently I thought I knew – my electronics and new loudspeakers. Now I am not so sure anymore.

Now the Kronzilla is a device that gives lots of joy from listening to music, but at the same time it makes one meditate, it responds to some questions while posing new ones. It sounds in an incredibly vivid, a bit “soft”, but in the good meaning of this word. Its interpretation of discs like the reference re-master of Winston Ma of the recordings Happy Coat Shota Osabe Piano Trio (Sho Studio of Music/First Impression Music, LIM K2HD 031, CD) is breathtaking. If I had to point to a sub-range that dominates the character of the whole then it would be – this is really not hard to guess! – the midrange. For 90% of the discs we get only their good points. Sometimes there can be too much of the good, even with such precise loudspeakers like the Dobermann – that was the case with the beautiful, fantastically recording The Rosary Sonatas of Biber (Harmonia Mundi, 907321.22, 2xCD; review HERE), or with the badly recorded, but musically fantastic disc Intermodulation of Bill Evans. The violins from Sonatas had a bit too “wooden” sound, they had a bit too much of the lower midrange, that made them a bit warmer and closer. This latter parameter, the volume of the sound, can be adjusted. The Kronzilla is a power amplifier with a passive preamplifier and it behaves like that. From a certain point, somewhere in the middle of the volume stops increasing in a noticeable way and the sound only gets bigger. Also the Evans’ piano that needs that timbre to be reproduced properly, but with a better resolution of the lower midrange. The Czech amplifier played it nice, but I know that it can be done better.

But, like I mentioned, this is only one of the interpretations of that what we call “absolute sound”. The Kronzilla has much weaker led bass than I am used to, and that annoyed me a bit in longer perspective. This sub-range is shown mostly like a large spot of sound, without such a clear drawing and contours as with the Luxman, not mentioning the Krell. This is not very disturbing, because there is not a lot of it, and the upper range is beautiful, but it is audible. Because starting with the upper bass we have a phenomenal timbre, this element is not easy to spot from the beginning. Above that, when we deal with long, sustained sounds, like on the disc from Jarre or on the Spiritchaser Dead Can Dance from the new Mobile Fidelity re-master (4AD/Warner Music Japan, WPCB-10078, SACD/CD), we get quite a strong and saturated base. But when it is about quicker playing, like a bass guitar or a low played double bass, then it gets worse. At least with loudspeakers like the Dobermann. Actually this is quite a simple load, when it comes to low frequencies, because the impedance is kept quite flat at 6Ω. The Kronzilla can be factory set to 4 or 8Ω. The tested unit was set to 4Ω and it was optimal for those speakers. But even 50W was not enough in this case. I think that the damping factor might have played a role here, as it is quite low, at 2.8. Because the Czech company exhibits on shows with tube loudspeakers, I listened to the amplifier also with such speakers – the model Uno Picco Avantgarde Acoustic. And yes - the dynamics, at home slightly quieted down, was much better here. Also the bass changed, but this is quite normal, as the loudspeakers have an active bass module. At the same time I missed some of the resolution I have in my system. The Kronzilla is not the most resolving device on the market. This is one of the characteristics that must be verified before the purchase. When it is about the relationships between the instruments, etc, it is brilliant. In the boundaries of the individual instruments the texture, drawing and definition are a bit averaged. Like I mentioned, it does not prevent from kneeling down with discs in our hands, but is an element, that will not convince everybody.

Regardless of everything, it must be said, that this is a fantastic device. Inside its limitations. Now every device has limits, so we just need to check, if the set of assets it carries is the one we think about and dream of. If yes, then we are in musical Eden and we will not want to leave it. For me personally, this is Eden, but not to full extent, one with a “but” hidden somewhere. I do not know a competition for the Kronzilla at this price level, that would combine all this elements I fight for in one whole. That’s it. The rest is only music…


The Kronzilla SXI-S is a hybrid integrated amplifier. Differently than usual, here are semiconductors on the input, and tubes in the current section. The latter, the power triodes T-1610, are manufactured by KR Audio themselves. They allow supplying 50W of power in class A single-ended. They draw the attention first. But when we need to move the unit, we get tubes in our eyes. This small chassis weights 50kg. The chassis has a low profile. Its front is made from stainless steel varnished black. The top is made from polished steel, below it a plate of 3mm thick black steel is placed, and the sides are from elements resembling a heat sink. But in this case the horizontal fins are only used to strengthen the chassis; otherwise the unit might break in half. The same heat sinks are mounted on top of the transformer casings. They also do not get hot, so probably their goal is to reduce vibrations. Hot gets only the casing of the last element as seen from the front, the power supply. There the whole power supply is placed, starting with a big toroidal transformer, placed vertically and even bigger choke for the anode voltage for power tubes. The transformer has also separate windings for the semiconductor parts and the heater voltage (5V, 3.8A). But I did not finish describing the amplifier. In the front we have a small knob for setting the volume with a red led showing its position and five small buttons reacting to touching. One of them turns on the amplifier, the others choose the input. The anode voltage is not on from the beginning, only when the led on top of the power switch changes color from red to green. In the back we have four line inputs with nice RCA sockets and the preamplifier output connected by a gold plated crimp to the power amplifier input. This is an extra element, not present in the standard version. To the sides we have two pairs of speaker terminals, from the WBT “safe line”. Next to them, below a bolted plate, we have an impedance selector. It is factory set to 4Ω. Far to the left we have a mechanical power switch and an IEC power socket.

After unscrewing the bottom plate it turns out, that the signal from the RCA sockets is switched in very nice relays and then, by means of a very long shielded cable, runs to the front, to the Alps potentiometer from the “blue velvet” series. From there it goes to the back to the back plate and then to the PCB. This gives about one meter of interconnect. So it is worth to try the version without the preamplifier-power amplifier separation. It is a pity, that the potentiometer was not placed on the PCB, because this would allow to get rid of about half a meter of the cable. On the PCB a simple amplifying setup was mounted – in the input we have two low power transistors, and the control section of the power tube medium power FET type transistors. The circuit is really simple, and most of the PCB is occupied by power supply elements. The stabilizers for the heating of the end tubes are mounted on small PCBs with stabilizing elements and very big rectifiers mounted to the side panels. So the fins on the outside have a purpose… A separate PCB is occupied by the standby and automatic bias sections. The power tubes are constantly monitored, and the bias is modified in real time. The circuit is very simple, but nicely made. And the transistor controlling the end tube is coupled via a Wima polypropylene capacitor. As we can read in the company materials, there is no feedback in any of the stages (0 dB).

Technical data (according to manufacturer):
Output tubes 2 x T1610    
Output power 2 x 50 W RMS (THD=3%)   
Frequency response 20 Hz-20 kHz (-3 dB)   
Load impedance 4, 8 Ω (selectable)    
Output voltage 0,75 V RMS/47 kΩ (at 50W output)
Dimensions (w/h/d) 385 x 415 x 550 mm    
Weight 50 kg 


Price: 39 000 zł

Distribution: SoundClub


SoundClub Sp. z o.o.
ul. Świętokrzyska 36/45
00-116 Warszawa

Tel. 022 586 3270
Fax. 022 586 3271


WWW: KR Audio




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