KR Audio Electronics Kronzilla SX-Eco Hybrid SET Power Amplifier (Hi-Fi+ 85)

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KR Audio Kronzilla SX-Eco
KR Audio Electronics Kronzilla SX-Eco Hybrid SET Power Amplifier (Hi-Fi+ 85)

In the world of high-fidelity, big generally equates with good and bigger with even better. These days, being asked to part with nigh on £30,000 for a 50 Watt per channel power amp isn’t going to provoke headlines, even if that amp is a single-ended design, deriving that output from a single device a side. The 50kg dead weight, whilst it’s physically impressive, doesn’t break new ground either. But what on earth are we to make of output tubes that are each the size of a serious anti-tank round? The weight alone tells you that there’s plenty of metal in the power and output transformers and they are pretty imposing – but they are de-warfed by the associated glassware.

Okay, so how big is big? Try on 300mm tall and 85mm in diameter – or about the size of my (fairly meaty) forearms. These are big, big tubes. So big in fact, that combined with the severe black and deeply finned chassis and transformer housings, that the Kronzilla would look perfectly at home on the set of a particularly dark and brooding Batman movie – except that the props department would probably reject it as over the top! They are actually T1610 output tubes, designed and manufactured by KR in their own Czech factory, high-powered, all-new direct heated triode designs that bring the origins of valve technology slap, bang up to date. And if appearances are anything to go by then this amp clearly means business, an impression that’s reinforced by the gentle quiver, the quickly dissipated huummmm as you power it up. So if big is good and bigger is even better, what does that make the Kronzilla? Well worth a look and listen, that’s what.

Not that this amp is all about mass and muscle. Indeed, one of the serious associated problems with all that hot glass is the effect this amp has on the ambient temperature of your listening room. No doubt welcome on a dull autumn day in Dunstable, high-summer in the UK, let alone the tropics, makes this thermal dissipation an uncomfortable addition to your listening experience. Enter then, KR’s solution – which, with stunning originality, they’ve dubbed Green Power.

The various Kronzilla amps (there are five models in the range, including an integrated and mono-blocs) are all hybrid designs, using solid-state circuitry to drive the output tubes: So why not just add a second, basic, solid-state output stage that can be selected for less critical listening? It’s one of those lateral suggestions that comes winging in from way out in left-field – and normally gets dispatched straight back out there. Except that in this case, KR were open-minded (or just plain mad enough – they did design those tubes!) to take it seriously, making the Kronzilla SX-Eco a hybrid in more ways than one. Is it a problem worth dealing with? Let’s just say that the vast majority of the listening for this review occurred during a distinctly average British August, but the effect of the KR amp on the listening room’s temperature was all too apparent: and this is a big room with a lot of height. In this case, the thermal impact was considerably greater than that of the 16 KT88s in a pair of VTL 450 mono-blocs; thankfully I didn’t need to fire them all up together. Of course, the Kronzilla’s heat signature is aggravated by its class A nature; any power that’s not used to produce music can only be dissipated as heat – which goes some way to explaining the amp’s appearance. All those black fins are for more than just show and in use the entire chassis is more than just warm to the touch. Depending on your point of view I guess you’ll either conclude that this is a seriously serious amp – or a seriously inefficient space heater. Actually, it’s both, but more on that later…

Operationally, there’s not too much to say about the KR amp – but what little there is, is quite important, mainly because it’s not covered in the instruction manual. Installing the tubes is easy enough; align the four, jumbo-sized pins and slide them home. But in doing so you’ll notice that the valve sockets are numbered. Logic suggests that somewhere on the valve (normally written directly on the base or on a small sticker) you’ll find a corresponding number, ensuring that the correct valve goes in the correct place. Well, on the Kronzilla you could spend a long time looking, ‘cos the relevant number is stamped on a small plate, actually inside the valve and perched right on top of the internals. That’s a first for me! Secondly, the small switch that selects the Green Power setting is on the rear panel, and although it’s labeled, there’s no indication as to which setting is which – unless you start peering at the inside of the tubes to see if they’ve lit up. Come on KR, if you are taking the eco-argument seriously then that switch needs to be on the front-panel and you need an LED or some other clear indicator as to the output mode selected.

Other than that, the main complication when it comes to installation is simply the massive weight and awkwardness of the beast. You can do it with one (if you’ve had your Wheaties) but I’d strongly recommend taking life easy and enlisting a second pair of hands, especially if you are planning to manoeuver it into a rack, where the lopsided weight distribution will be a real challenge. Hook up is simplicity itself, with just two RCA sockets and single sets of five-way binding posts to deal with. On arrival, speaker impedance is set to 4 Ohms, but this can be adjusted by removing the small cover plate between the speaker terminals and shifting the internal grub screws from the top two sockets to the bottom ones – with the power switched off! The setting values for these are noted in the manual and also on the inside of the cover plate. The bias circuitry is auto monitored and self adjusting, meaning that’s a chore you won’t need to worry about, while also ensuring that the tubes operate under optimum conditions at all times. If a tube should fail then the amp automatically defaults to standby, a sensible precaution given the sheer size of the output devices and the potential ramifications if they ever decided to leave
the reservation.

The Kronzilla designs, with their hybrid topology, triode output devices and healthy Class A output could easily find themselves in some sort of philosophical no man’s land, with enough conflicting technology to alienate just about everybody, but as soon as you listen to one there’s no escaping the fact that it’s the SET content that dominates the sound. Put the SX-Eco into a system in place of a push-pull alternative and you’ll notice an instant loss of pace and low frequency attack. Does that mean that the KR amp suffers from the limp-wristed lack of bass control that bedevils so many single-ended amps. No. What it means is that you need to understand that most SETs offer a different energy spectrum at low-frequencies, a fact that demands you adjust your speaker placement to compensate – or, in the case of the Focal Stellas, crank up the EM damping a notch*. Do that and things fall back into place. Okay, so the SX-Eco doesn’t possess the bottom-end authority of the VTL 450 or Rowland 625, but make sure that the system set up and placement is properly matched to its performance and it’s capable of providing proper musical support, a substantial foundation for the mid-band – which is just as well because that mid-band is what this amp is all about.

Rich, lush and colourful, the KR midrange reads like a cliché list to describe all those SET virtues that fans wax lyrical about. Thankfully there’s none of the syrupy wash and rhythmic imprecision they also overlook. The presentation is deep, spacious and fluid, with an easy sense of unforced tempo that’s relaxing and inviting. Familiar voices are natural, with a truth of character and accent that easily evokes the original, while the tonal separation of instruments (horns from woodwind, violin from viola) is so apparent that you wonder why it should even be an issue on other amps. In the Pentatone recording of the Mozart Sinfonia Concertante (K. 364) the quicksilver brilliance of Julia Fischer is perfectly balanced by the smooth bowing and fluid phrasing of Gordan Nikolic, the beautifully controlled orchestral support of Kreizberg and the NCO. But as wonderful as the KR’s rendition of this great performance is, there’s also a lesson to be learnt here. I found myself backing off the volume control by a notch, playing the piece a little quieter than I am used to (at least that’s the way it seems, but more on that in a moment). If you audition the SX-Eco, try it and you’ll hear just what I did; as you reduce the level the sound stage simply opens up in front of you. It’s not a big adjustment, but it makes a huge difference, not just to how spacious the presentation is, but how fluid, how controlled and how much headroom is available.

That lesson is simple; don’t get carried away by the sheer size of those bottles, or the decent (for an SET) power output. The Kronzilla is no powerhouse, at least not in the sense of the VTL or Rowland amps I mentioned earlier. Even with the 95dB sensitivity of the Focal Stella and with the amp set to its 4 Ohm taps, it was all too easy to push it outside of its comfort zone. Ask for a little too much and the sense of acoustic space shuts down, the dynamic contrasts compress, drums lose their snap and impact. The whole sound softens and starts to congeal. Push harder and things quickly get glassy and glutinous, with an unpleasant glare infesting proceedings. And bear in mind that it might not be you doing the pushing: take an album like Aimee Mann’s Bachelor No 2; tracks like ‘Nothing Is Good Enough’ or ‘Satellite’ can be comfortably played at a level that puts the amp well into the red as soon as the raw aggression of ‘How Am I Different’ gets going. Not only do you lose the cosmetic elements of the sound described above, but the drums sog and the lyrics lose the sardonic edge on which they depend, especially the chorus. Sure enough, back off the volume and things soon fall into place. So, whilst the power rating allows the Kronzilla to embrace lower efficiency speakers than its flea powered brethren, anything approaching an awkward load should still be considered strictly off limits. The Stella might be benign when compared to the Grande, but substituting the Coincident PREs with their virtually flat, 8 Ohm impedance characteristic shows just what a difference the loading makes to this amplifier. Suddenly, levels were far less restrictive, headroom never an issue.

There’s a second contributory factor to this particular problem, one that stems from the sheer quality of the Kronzilla. The harmonic and tonal purity of the sound it produces, the natural warmth and lack of edge fools your ears. Deprived of the usual cues that indicate higher levels and early onset distortion, there’s a tendency to play the amp louder than you realize.
Although I’m suggesting that you back off the volume, paradoxically that doesn’t necessarily mean you’ll be playing it quieter; at first it might seem that way but whip out an SPL meter and you’ll soon discover the truth. All amps benefit from care when it comes to matching them to speakers; just be aware that the Kronzilla needs a little more care than most and the range of partners is narrower than the numbers might suggest. Don’t be tempted to run it too close to the ragged edge. You’ll quickly get a feel for where it’s comfortable in your own system, but don’t be surprised if just occasionally you find a recording that catches you out.

Of course, in the same way that speaker choice impacts the performance of the power amplifier, its character can also be tailored through choice of line-stage. Ringing the changes between the Pure Sound L300 (temperamentally and topologically perhaps the logical choice as a partner for the Kronzilla), the JRDG Corus and the Connoisseur certainly tilted the performance this way and that, but it also demonstrated that in musical terms, the KR amp was the dominant partner. Listen to this amp and if you fall in love with its sound and presentation it’s the easy fluidity, the rich colours and sense of sheer physical presence that will make you swoon. But in other regards it might leave you cold. Even with the Connoisseur(s) doing the driving, the system lacked an intimacy and low-level resolution I’m used to. It’s down to a lack of micro-dynamic information, which robs notes of leading-edge detail and texture at the same time as it adds to that sense of liquid smoothness. Take the Berglund/LSO recording of the Sibelius 2, the opening pizzicato passage of the second movement: the quick tempo is easily followed, each note pitch perfect, the fluid presentation giving a real sense of shape and progression to the phrases – something that they can sometimes lack on higher-resolution but more temporally fractured electronics. But listen into the playing and it’s hard to hear where each note starts and stops, its exact shape. The phrasing is masterly, but the note-to-note definition is certainly wanting.

Even more interesting is a switch to the Barbirolli/RPO recording (the Chesky re-issue). That same pizzicato passage is woolier to start with, so no surprise that the notes are softer and more rounded here. But what’s more striking is the similarity in the tonality and acoustic presentation of these two (quite different) recordings. This is the character – warm, rich, smooth and flowing – that the Kronzilla imposes on proceedings. Even music as notoriously spiky as La Folia gets taught some manners! It’s a characteristic that needs to be balanced against the sumptuous musical quality, the convincing scale and presence of the amp, it’s uncannily natural midrange tonality and lack of electronic edge. This is an amp that will allow many hours of rewarding and fatigue-free listening, that avoids any hint of electronic thinness or etching to its sound. But judged by the very highest standards, it’s also an amp with a distinctive character and presentation – one that will contribute to the performance of the system rather than simply passing you the performance that is on the disc.

For the listener looking for all those traditional triode strengths – the lush colours, tonal truth and lack of edge – the KR amp delivers in spades. But it also brings a clarity of purpose and overall musical coherence to proceedings, a way with scale that can make orchestral music truly convincing and a deft grip on things temporal and rhythmic that keeps things moving. The Eco switch is a useful development – more so than I thought it would be – but ultimately the amp must stand or fall on its sonic merits and those are considerable. Far from the typically polite and fuzzy SET crowd, it takes the triode high-points and grafts on enough of the more mainstream high-end virtues to seduce many a listener. It’s not without flaws, but then what is? If you like what triodes do, but you want more: more power, greater rhythmic integrity and more attitude – then the Kronzilla could well be the amp for you.

For me, it’s a mistake to try and push products in a direction they don’t want to go; “compensatory” matching of components is all too often a case of two wrongs not creating a right. Whilst I loved the dynamic range and sheer power delivered by the Connoisseur, the L300’s natural substance and drama allowed the KR to flaunt its strengths – rather than trying to cover up its weaknesses. In the same way, as impressive as this amp is bringing welcome warmth and colour to CD, it really thrived on the natural space and harmonic delicacy of vinyl sources. If you fall for the Kronzilla – and there are many who might, many good reasons why you should – give in to its demands and feed it what it wants. One look at those tubes tells you all you need to know about the nature of this product: give it a chance and go for broke. Anything else is like going to a Cordon Bleu restaurant and avoiding the dishes with cream in them!

Technical Specifications

Type: Hybrid tube power amp with additional “Eco” solid-state output stage
Valve Complement: 2x KR T1610
Output Topology: Single Ended Triode
Rated Output Power: 50 Watts/8 Ohms
Input Sensitivity: 1V
Damping Factor: 2.9
Global Feedback: Zero
Power Consumption =
Tube Output Stage: 500VA
Green Mode: 5VA at idle
Dimensions (WxHxD): 385 x 415 x 550mm
Weight: 50kg
Finish: (Very) Black
Price: €14,995 (per channel)
Manufacturer: KR Audio Electronics sro Czech Republic
Tel. +42 02 8186 4217
Fax. +42 02 8186 4343
Net. www.kraudio.com

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