KR Audio Kronzilla SX1 Mk II

Price: $16,500


Dr. John Richardson

2nd Opinion by

James L. Darby

I had the pleasure recently of attending my first Rocky Mountain Audio Fest. While this was not my first audio show, it was somewhat unique. What I most enjoyed was the positive interaction between the press, consumers, and manufacturers/designers in a friendly, open environment. This is how I first came to know of KR Audio, a company that manufactures vacuum tubes and tube amplifiers in the Czech Republic.

It was somewhere in the late afternoon on Friday, the first day of the show, and I was starting to feel overwhelmed. I needed respite and relaxation. I got to the end of a long hall, took a left, and dead-ended at a room off the beaten path. There were no crowds around, and all seemed calm. Ahead of me was an open door beckoning me into a warm, comfortable room; inside was a salt-and-pepper-haired man with a quick smile and friendly greeting. This gentleman, as I was soon to find out, was Mr. Cor Dekker, of Musical Reality, the Benelux distributor of KR Audio. Cor must have sensed my frustration, as he quickly seated me, put on some soothing music and began the run-down of the system at hand, which consisted of Von Schweikert speakers and a lovely sounding compact disc player from France. The system sounded beautiful; it was dynamic and involving…. Musical! What immediately caught my eye, though, was the strange looking integrated amplifier with two massive output tubes that was driving the Von Schweikerts. This monster was the brand new KR Audio Kronzilla SX1 MkII amplifier, which was being debuted at this show. I just couldn’t stop looking at the thing as the music washed over me and took my cares away.

Well, the next day, after meeting up with my Stereomojo compatriots (James and Linda Darby, along with Bill Schuchard), we all made our way back to that magical room. Inside, we got to hear the system, and right then and there, we decided to name the Kronzilla the best new tube amplifier at the show. At that, we gingerly inquired about the possibility of reviewing the amplifier, and Cor Dekker immediately told us that he would see to the arrangements. The long and the short of this story is that within two weeks, I had that very same amplifier sitting in my listening room. I should mention that the amp itself weighs in at over 100 lbs, so getting it up two flights of stairs to my attic man cave was an adventure in itself. I think I’ll forgo the heroics going the other direction and get another audio “buff” to help out.

Before getting into a description of the amplifier and its sonic characteristics, I’d like to say that it has been a pleasure to work with all of the folks associated with KR Audio, from Cor Dekker, to Dr. Eunice Kron (the CEO), to Dr. Bradley Smith (the U.S. distributor, who also had a hand in the development of this new Mk II version). These people have been wonderfully helpful and have readily responded to all questions I have had about the amplifier and its history.
Let’s then start with a rundown of the amplifier itself. The Kronzilla (as I’ll refer to it from now on) is a hybrid design that utilizes both solid state and vacuum tube amplification stages that retails for $16,500 here in the States. While this design approach in and of itself is not unusual, the Kronzilla does things a bit in reverse in that it uses a solid state input stage followed by a vacuum tube output stage. Such an approach is not unique, but it is somewhat unusual. When I asked why the designers decided to go down this road, Dr. Smith told me that it was because they wanted to build the amplifier around the mammoth T1610 triode tube, which was designed by and is exclusively produced by KR Audio. In other words, it is too good a tube not to use as an output device! However, other forces were also at play. Quoting Dr. Smith: “ …the T-1610 tubes can be very difficult to drive because of their relatively low input impedence due to the cumulative effects of the parallel triode elements. To drive the tube requires some power, so a FET is used to maintain linearity whilst driving large voltage swings. The hybrid design allows the FETs to do what they do best (produce current) and the tubes to do what they do best (swing large voltages). These amplifiers use the mix of devices that complement each other.”

This T1610 tube itself is a thing to behold. It is around 13 inches tall (presumably to accommodate the parallel triode elements mentioned above) and is capable of putting out up to 50 watts of pure, single-ended class-A power. The tubes are beautifully made by hand using thick, artisan-blown glass and shiny brass bases. Each one is a work of industrial art; I had never before seen anything like them! I figured that they must be expensive, so I asked about their typical life span. I was assured by both Drs. Kron and Smith that these tubes last from 8,000 to 12,000 hours, and virtually no amplifiers using the T1610 have had to be re-tubed. Not a bad track record, given that the first amplifiers using this tube were sold in the late 1990s.

I asked Dr. Smith to go a bit further and summarize what he thought were the greatest strengths of the Kronzilla. Again, quoting the good doctor:
“The number 1 strength is single ended operation. This means that the audio wave is processed by a single output tube. There is no hand off of the waveform as can be found in push pull operation.”

“The number 2 strength is zero feedback. The SXI MK II uses no global or local feedback. Control is facilitated with high-end output transformers. Authority is provided by the sheer power provided by the T-1610 tubes.”

“The number 3 strength is the pure class A operation of the amplifier, which is dictated by the single ended topology.”

“The number 4 strength is design execution. Attention [was given] to power paths, ground paths, signal paths, passive and active component selection.”

“The number 5 strength is the simplicity of design. The signal only passes through four active elements between input and output.”

When queried about potential drawbacks, Dr. Smith mentioned the heat associated with class A operation, as well as the massive iron, which makes the amplifier heavy and hard to move. Tell me about it… Oh, yes, and my own gripe, minor as it may be: the tubes don’t glow! Darn it, a tube that beautiful should glow softly in orange or blue at night, just to make sure the owner doesn’t forget that it’s there. I noted just a bit of light coming from the sides, but it’s not really visible from a normal listening position.

With respect to features, the Kronzilla offers four sets of high-level analog inputs (but no in-board phono stage), as well as a standby switch and a single motorized volume control on the front panel. All of these features are accessed either from the front panel or via an included remote control. The latter implement, while handy, was plastic and cheap looking: definitely not in line with the rest of the quality of the amplifier package. On the rear panel are four sets of sturdy, high-quality RCA input jacks along with an on/off toggle switch and binding posts. Hidden between the binding posts is a “secret” compartment that houses the four- and eight-ohm output transformer taps; I opted to use the eight- ohm taps with my Shahinian Compasses. There is a solid metal remote that operates smoothly and precisely.

Normally at this point in a review, I’d be chomping at the bit to summarize the most obvious sonic characteristics of a piece of gear. Not here, as this amp turned out to be something of a chameleon from the get-go. From where I stand, I think that a chronological rundown of my time with the Kronzilla might be more useful. Such an experience can be frustrating, but it can also be very rewarding, because it can cause a person to learn more about their system, thus ultimately getting him or her closer to the “absolute sound.” Isn’t that one of the joys (and frustrations) of the hobby?

That said, let’s start from the beginning.

Upon receiving the Kronzilla and hauling it up to the listening area, I immediately took the analog output of my Eastern Electric Minimax DAC and patched it into one of the inputs of the amp. I then tied in my Shahinian Compass speakers and let the music rip from my Mac Mini, using the Metric Halo ULN-2 as my firewire to S/PDIF converter. After listening for a while to make sure all was properly connected, I noticed that the musical presentation was a bit thinner and more anemic than I’m used to. I didn’t think too much of it, as the amp still needed a few hours of warm up time (recall that it hadn’t seen power for about two weeks). Unfortunately, the more I listened, the less engaged I became. Hmm, was this the same amp I heard in Denver? Not all was negative: the Kronzilla came off as exceptionally fast, lithe, and resolving. It just didn’t seem to have the “wow” factor I had experienced before. More specifically, I didn’t hear the depth and bass punch that I am used to, and the midrange seemed threadbare. Maybe the amp just wasn’t as colorful as my Threshold SA3.5e amp/Wyetech Coral preamp combination, and my ears just needed time to adjust to the change.

I really couldn’t come to accept what I was hearing. From my experience in Denver with the Kronzilla, I knew it could sound way better than it did in my listening room. Then it struck me. Maybe this thing is so transparent that it’s revealing problems elsewhere in my system. I got down to work and started thinking. The most obvious culprit I could come up with was that long analog interconnect run (roughly 17 feet) from my DAC to the Kronzilla. We know that long cables can act like antennas and also pollute small analog signals with unwanted resistance, capacitance, and inductance, all of which ultimately degrades sound. They can also provide an impedance mismatch between source and amplifier. To correct this possible problem, I placed the DAC very close to the Kronzilla and connected the two with a half-meter run of Kimber Silver Streak interconnect. I used a long, shielded coaxial cable to get the digital signal from the Metric Halo to the DAC.

OK, now we’re talking. I could immediately hear a profoundly audible difference. Any grunge that was present was gone, and the sound, top to bottom, became much more fleshed out. It was as if the Kronzilla went from a mere lizard (OK, maybe a Komodo Dragon) to, well, the monster that leveled Tokyo! Now, the magic that I had heard at RMAF was back. I also noticed, for the first time, the tremendous depth of the soundstage. I could hear instrumental images starting at the front of my speakers and moving backwards to somewhere around the rear wall. Now that this bad boy had my attention, I was ready and willing to do some serious listening.

Of late, I have been exploring the music of Arnold Bax, one of the more interesting British composers of the 20th century. Among many works, he wrote an intriguing cycle of symphonies. A favorite among these is his second symphony, which is dark and brooding, with occasional angry outbursts. My listening notes are based on my high-resolution digital rip of the Lyrita stereo LP (Lyrita SRCS 54). I noted that the Kronzilla was fast, with no image smearing while retaining very good separation of instrumental lines; there was no sense of congestion whatsoever. I also marveled at the wonderful sense of soundstage depth of this recording, which is one thing that makes listening to these complex works so engaging.


Keeping with Sir Arnold, I next listened to the Andante of his lovely Sonatina, performed by Wilfrid Parry (piano) and Florence Hooton (cello) and recorded in the late 1950s by Richard Itter, Lyrita’s founder, right in the music room of his home (mono LP, Lyrita RCS 6). While this isn’t the most resolving recording I’ve heard, it has a wonderful sense of immediacy about it that makes it very interesting to listen to. You can’t help but to sense that you are taken back in time to Mr. Itter’s conservatory hearing this wonderful musical event go down in real time. Here, the Kronzilla clearly presented the cello just forward in the soundstage relative to the piano, with a wonderfully “woody” quality to it. I could easily tell that Ms. Hooton’s playing was a bit rough and aggressive, with a nice sense of attack, both in her bowing and her pizzicato.

I suppose that this is as good a time as any to relate one important item: in my experience, the Kronzilla just doesn’t sound like a traditional vacuum tube amplifier. Even with those huge bottles up front, the huge lizard sounds clean and exceptionally uncolored. I just couldn’t detect any kind of distortion, not even that nice-sounding even harmonic stuff that makes people like the sound of classic tube gear. It just wasn’t there. I heard a wonderful sense of immediacy, which one would expect from a single-ended design such as this with a minimum number of gain stages. It was as if there were essentially no barrier between myself and the music. Of course, I would suggest that such a presentation might make for something of a conundrum for many audiophiles: we often like our recorded music to sound nice and pleasing, even if that’s not what’s coming directly from the mic feed. If truth is what you are after, with no lipstick on the pig, then the Kronzilla could well be your amp.

Turning next to jazz, I cued up my digital rip of the Modern Jazz Quartet’s classic album Pyramid (stereo LP, Atlantic SD-1325). Here, on “How High the Moon,” the bowed string bass sounded absolutely exquisite, with plenty of heft and body and none of the bloatedness one sometimes hears when that instrument is poorly reproduced. Milt Jackson’s vibes sounded delicate with plenty of decay, and I could easily differentiate each individual mallet strike. Interestingly, I noted no real center image. The drums, bass, and piano seemed to be panned hard left, while the vibraphone leaned to the hard right of the soundstage. Images extended way beyond (and somewhat behind) the speakers on both sides. Again, due to the resolution of the Kronzilla, I suspect that this is an artifact of the recording itself. Likewise, on Stanley Turrentine’s album “Let It Go” (stereo LP, Impulse A-9115), the sax sounded absolutely huge, as we would expect from Turrentine, and it was holographically reproduced beyond the left speaker. Shirley Scott’s Hammond organ took on a nice, dreamy quality as it inhabited the center of the soundstage, placing itself nicely to the rear.

So far, so good, though all of this still begs the question: is the Kronzilla too lean from a tonal perspective? I’d argue not, as I found that I could listen to it for extended periods of time with no sense of fatigue whatsoever. I also didn’t grow bored with it as I have with some other components. I’ll admit that I don’t mind a little bit of extra body and warmth in my stereo playback. My present combination of Threshold SA3.5e amplifier and Wyetech Coral linestage provide just the right amount of these things for me; I suppose that’s why I choose to own them. Are they the ultimate in accurate reproduction of what’s on the original recording? I don’t know, but I suspect not. Do I truly care? Not really. Even if the Kronzilla is more accurate and resolving, I still found it to be a highly engaging and enjoyable listen.

A case in point is Eva Cassidy singing her rendition of “Over the Rainbow” from her posthumous album “Songbird” (CD, Blix Street). I was first introduced to this cut by Jack Caldwell of Holistic Audio Arts, when he came to drop off his lovely H1 speakers for review. Sad as Eva’s story is, most folks agree that she had phenomenal voice control and dynamics. She really makes one think that she owns the song; others have said this, and I agree, as she sings with emotion that is hard to match. On “Over the Rainbow,” try to tune out the cheesy synthesized oboe and strings and focus on Eva’s singing and picking. My listening notes suggest that I ultimately preferred her presentation with my house amplification, but that the Kronzilla was no slouch. I noted that the Kronzilla reproduced Eva’s voice in a highly musical and engaging manner, with no hint of strain or hardness. Maybe it didn’t quite have the body and midrange glow that my Threshold offered, but it was highly musical nonetheless. I’d have to say that to me, the Kronzilla sounds about like I’d expect the cleanest, fastest, most resolving solid-state amplifier that could be produced today to sound. Granted, I haven’t heard this mythical amplifier, but if someone asked me to describe it, I’d use the Kronzilla as my starting point.

So ultimately, what have we got here? The Kronzilla is expensive, at least by my standards. For $16,500, this amplifier offers a nice built-in preamplifier section with plenty of analog inputs and the motorized volume control, as well as 50 watts per channel of single ended vacuum tube power on the output using those state-of-the-art T1610 bottles. It is also exceptionally lithe, immediate, resolving, and dimensional. Quite simply, the music poured forth with an ease that I have not heard from other amplifiers, and this quality alone qualifies the Kronzilla, at least in my book, as perhaps the best overall amplifier I have had the pleasure of spending quality time with. Oh, and did I mention that the Kronzilla is assembled here in the good old U. S. of A?



James Darby

As usual, the good doctor has precisely nailed the character of the mighty Kronzilla. I also experienced a very short-term bout of “leanitis” at first, the sound of the amp bore no resemblance to what the four of us had heard in Denver. Not only did it sound rather anemic, I could turn the thing all the way up and still hear only a moderate volume level. After about five minutes, I simply turned up the output of my Eastern Electric Minimax DAC from its two o'clock position to full output and voilà, the beast was back! What I was hearing from my Vaughn Cabernet speakers was even better than what we heard in Denver, and that's saying a lot. The bottom end was prodigious, detailed and exceptionally musical with unbounded control and an extreme abundance of texture. The grinding bass fiddles in the “Pirates of the Caribbean” soundtrack cut “The Kraken”, one of my most severe torture tests, were rendered perfectly with all the shock and awe the track entails. This track starts simply with low strings playing a simple melody and escalates to one of the most bombastic and complex orchestral tsunamis on record. The big KR not only aced the test, but did so with little effort. I could almost see the big tubes grinning at me as if to say, “Is this all you got? Come on, gimme something more challenging!”


THIS is what I got!


Okay. I threw some raw pipe organ in its cage in the form of Jean Guillou -The Great Organ of Saint Eustache, Paris” via a high resolution 24/96 file from Linn Records. Jean was playing the infamous Bach “Toccata and Fugue In D Minor”, a piece I have played many times on many monster pipe organs, so I know it intimately. With a diabolical smirk on my face, I cranked it, throwing the challenge right back at the Kronzilla at levels exceeding 100 dB. The French cathedral has a reverb time of at least 6 seconds, making it difficult to reproduce the furious passages cleanly without severe smearing. The massive organ filled the room with the sub harmonic pedal pitches rattling some picture frames and not a hint of smearing.



However, in this case it's the only word that fits; the sound was simply awesome. The organ floated well behind the speakers with an image that extended the width of my24 foot room, well beyond the speakers, and up to the 20 foot ceiling with unbridled power and the diabolical emotion the piece depicts - it's often been used in horror films, you know.

Convincing, involving, immersive and musical. I think the 50 wpc rating is very conservative, I would have guessed twice that even for a tube amp. Add powerful to the list of adjectives.

That power fits perfectly for a genre John didn't mention; the super beast rocks! Whether it's recent 2010 releases like “Guitar Heaven: The Greatest Guitar Classics of All Time” by Santana, or Heart’s “Red Velvet Car” or Even “High Violet” by The National, the amp delivered on pulse pounding rhythms and grooves without sacrificing the nuances of the human voice. The KR loves vocals.

Jazz? Ditto. It does not favor one genre over another, but rather testifies of its mastery of all.

John mentioned that the KR didn't sound like a tube amp. He's right about that, but it doesn't sound like solid-state either. It doesn't sound like an amplifier at all; it just sounds like music, and that's about the highest compliment I can give a component.

John was surprised that the towering tubes do not glow very bright. So was I, you only see a bit of orange filaments glowing. To me though,since we lsiten primarily in the dark, that's a good thing. Some amps light up the room like a bevy of 100-watt bulbs. While heat from the tubes is significant, it's not all that bad. If you have curious pets or kids, the twin towers could be a hazard if left within reach since there are no guards in place.

I've tried to be picky and extra critical in search of some shortcoming or weakness, but it's just not there. I'm sure others could, but it's more about personal taste and biases rather than absolute performance. John thought it might not have “the body and midrange glow” of his amp. I half agree. There is no tube coloration in the midrange, but there is certainly no lack of body, unless you equate “body” with “thickness”. It doesn't add any thickness or anything else to the midrange, but I've never heard an amp that digs out the body of voices and instruments that are present in any recording like the 'Zilla.

After several evenings of 3 to 4 hour listening sessions, Linda said, “This is the best our system has sounded”. She was right.

While definitely not a candidate for the new Stereomojo column “Audio for Cheap Bastards,” the KR Audio SX1 Mk II integrated amplifier, at $16,500, gives us a taste of what state-of-the-art, no holds barred, modern amplification is all about. While there is no way that I could seriously consider owning an amplifier like this (at least not at this point in life), I definitely appreciated it and savored my time with it… That is, once I figured out how to keep and feed it! If you take your time to optimize whatever comes before it in terms of source component(s) and interconnects, you will be generously rewarded with some of the cleanest, fastest, most immediate and dimensional sound you could ever want. To boot, it’s also a visual statement, especially with those beautiful T1610 vacuum tubes up front. If you have the bucks, it would be hard to do much better, and you could certainly do much worse spending as much or more.

Watch your back though, it is a BEAST!


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