KR Audio • VA910 Mono Amplifiers

by Ross Mantle | September 7, 2017


Many years ago, Marc Mickelson and I had a Saki-fueled argument in a third-rate Montreal restaurant about "voluptuousness" as a sonic property of audio gear. I said that the amp I owned at the time, a KR Audio 32BSI single-ended triode (SET) amplifier, had it. But beauty alone could not sway him. He also wanted truth. Over the ensuing years that debate seems to have had an impact on both of us. He came to want more beauty, and I more truth. Only relatively late, perhaps too late, have we realized, as Keats did, that beauty and truth are the same thing.

My original KR single-ended 300BXLS, which I bought in the early 2000s, was more involving, more voluptuous, more solidly three-dimensional and yet quieter, more precise and more accurate than anything else I heard at the time, which is why I spent an irresponsibly large portion of my meager dollars on it. The breakthrough nature of KR's early amplifiers, which used their own in-house, high-current version of 300B tubes (300BXLS) in an overpowered single-ended triode design, was a very good deed for audio.

But no good deed goes unpunished. KR went through various tribulations in the intervening years, including the death of founder Dr. Ricardo Kron, which might have felled a lesser company. Yet, today KR Audio thrives, continuing to make amplifiers with astonishing sonics that meet or define the state of the art. As an example, proprietor Eunice Kron, Dr. Kron's widow, tells me that the VA680i "Kronzilla" integrated amplifier just won "Best in Germany" at a recent show. Congratulations.

The subject of this review is a pair of KR Audio VA910 monoblocks. This is a longstanding design that has been reviewed in the past but appears to have been incrementally improved since. The VA910s have a solid-state input stage with push-pull tube output using four KT120 high-power output tubes producing a specified 160 watts each.

I e-mailed a number of questions to Marek Gencev, chief designer at KR Audio, to try to discover the ingredients in his secret sauce. The amps are push-pull class AB and run in class A up to 120W. This limits the maximum power, but increases fidelity because of a lack of zero crossover-point distortion when operating in class A, as they do most of the time. Each chassis contains two separate amplifiers, each with their own Lundahl C output transformers paralleled at the output. This, Gencev says, enhances frequency response and lowers noise. It would also, I would think, increase manufacturing cost.

The power supplies are unregulated with standard LC filtering. They are oversized with a large toroidal transformer. Due to oversizing, losses in the form of heat are low, and reliability is high. As we all know, cool-running components tend to have high reliability, because heat is the enemy of electronics. I was very impressed that the power-supply section of the amps never became hot to the touch during operation, only warm. This is in contrast to my older-generation KR from twenty years ago, which would nearly burn your fingers. Filament supplies are also unregulated -- just the standard AC heaters. There is no audible hum, which means the intrinsic noise cancellation of the circuit is excellent.

In other words, the high performance level of these amps seems to have been accomplished without any magic tricks or unusual circuitry, except perhaps for the solid-state input stage. Apart from that, what we have here is normal technology with abnormally good engineering. I also have the feeling that a good deal of listening went into the design, and that the KR heritage or house sound must have played some kind of guiding role. These amplifiers certainly sound much more like a typical KR than a typical push-pull four-banger.

According to Gencev, the tubes were chosen to meet the desires of some customers for a tube amp that doesn't rely on tubes for which KR is the world's only supplier. The VA910's KT120s, which are a high-power version of the beam-pentode KT88, are run in ultralinear mode. Until recently, the KT120s were only made by Tung-Sol, which was curious given KR's goal of avoiding sole-source supply. As of this year, however, Shuguang now also makes a Black Treasure version of the KT120. I wonder whether the Shuguangs might be warmer sonically than the Tung-Sols. It would be nice to try them.

My experience of the aesthetics and ergonomics of the VA910s was positive. They have a cool little soft-touch on/standby button on the front with a blue LED that brightens after a thirty seconds or so of tube warm-up. The warm-up time is appropriately brief and not annoyingly long, as with my old KR amp. This soft-touch switch is much more sophisticated than reaching around the back for a chunky rocker switch, and very welcome. There are no pops or crackles on activation. Crucially for me, there are both RCA and XLR inputs. I much prefer XLR: the physical connection is easier and better, XLR usually sounds better, and equipment with XLR connections is usually higher-grade. The speaker binding posts are also high in quality.

The amps are not behemoths. They are solid, but not backbreaking in weight. There is a high-quality, powder-coat-finished metal casing. The all-black, no-flash, look is understatedly attractive. I used the amps without the silver tube cages they came with, which I found unsightly. A cage is, of course, necessary if you have little children around -- for the tubes, not the children.

Very important for any tube amp, the VA910s gave me that "it just works" feeling of reliability (credit: Steve Jobs). They never got hot, always worked, and never complained. If I happened to leave them on all night, I didn't worry either about the amps or the house.

Reviewing these, as should be the case for any component, was not a single step, but rather a journey through various combinations of partnering equipment. I find it frustrating to read equipment reviews that only mention the partnering gear in passing, or not at all, as if the other links in the chain can be neglected. In fact, they are critical. I started with JMlab Mezzo Utopia speakers, a Linn Klimax DS/2 digital streamer/DAC (renderer) and the Coincident Statement Line Stage preamplifier (CSLS). Line-stage connections were XLR and all cabling was Coincident Statement.

I sat back, pressed Play, and my first thought was, Ah, yes, that expensive sound. Quiet background, no extraneous noises, big soundstage, and lots of control. It was the sound that expensive gear tends to have. Despite these good things, there was an unpleasant hardness at louder volumes, so I switched the JMlab speakers out in favor of a pair of Lansche 5.1s. These are German-made transducers with marvelous plasma tweeters. They are similar in sensitivity to the JMlabs, but with a pair of smaller woofers instead of a single large one. The Lansches also have much better resolution.

The presentation of the VA910 amplifiers through the Lansches was radically better. That expensive sound I heard at first turned into really top-notch sound. There were gobs of detail, no smearing of transients, superbly resolved highs and articulate bass, all with a certain "wet" quality you might call liquidity.

I switched out the Coincident Signature preamp for the P130 tube preamplifier from KR Audio, kindly provided by Eunice Kron with the amps. I heard some synergy, as would be expected of components from the same manufacturer working together. The KR preamp downshifted the tonal balance a little, giving more midbass emphasis. The somewhat darker balance was attractive, at the expense of a little more noise in the mids and highs compared with the essentially noiseless Coincident Statement. The P130 also resolved the soundstage in an uncanny way, with little sonic details precisely positioned not only side to side but front to back, some behind and outside the speakers.

Overall, I preferred the KR Audio P130 to the Coincident Signature with this combination of components, as it seemed to have a greater overall sense of realism. It displayed far better dynamics, better bass and better timing, resulting in closer emotional involvement. With a nod to my fellow Canadian, Israel Blume, the Coincident Signature is not only a class leader, but a screaming bargain. I went for the sonically uncompromised, non-remote version and fine-tuned the volume with my computer using the digital volume control built into the Linn control software. Now fed by two world-beating front-end components, the VA910s really sang. As others have alluded to when reviewing KR amplifiers, the soundstage was stupefyingly big. There was a room-filling quality, as if I were fully immersed. This is a nearly unique property of KR amplifiers and not reliably found among other manufacturers.

With regard to digital sources, music streamed through the Tidal subscription streaming service had detrimental sheen, edge enhancement and sibilance, while the same tracks sourced from the NAS drive did not. I took this as a demonstration of the transparency of the KR amps in this system. Presumably the difference was an artifact of the compression algorithm Tidal uses.

Overall, the performance to this point was very satisfactory, but the ultimate test was yet to come. Having plopped down an inordinate sum for the Katalyst upgrade to the Linn Klimax DS/2, I took delivery of the latest board-upgraded Klimax, the DS/4. This is one of the very best, if not the best, digital source in the world.

A word about this claim, and digital sources in general, before we move on. For years I’ve been searching for digital that can adequately replace vinyl, stubbornly rejecting record players and their associated arcana in the view that the functionality and immutability of digital would eventually prevail, if only the sound quality could compete. Long-term, I suspect that computer music will improve and take over music sourcing completely the way video streaming has taken over broadcast TV and VCRs. This is well underway already.

For now, the optimal approach for high-end music, in my view, is the digital renderer. This combines the functionality of a music streamer and DAC and uses networked media-server software for source data. Well-known, affordable exemplars are the Sonos, Logitech Squeezebox, and Bluesound products. Contenders to the crown of the very best sound quality in this category are on offer from Naim, Linn, Lumin and Ayon. Of the top models offered by these four, I’ve heard only the Linn. There is no shootout involving all of these that I’m aware of, but there are head-to-head comparisons of Naim vs. Linn and Lumin vs. Linn which seem favorable toward Linn.

With the system in peak form, it was time to run through some favorites. Paul Simon's "Everything Put Together Falls Apart" from his self-titled 1972 album [Columbia 25588-2] is on my all-time list. I again compared the Tidal version to the ripped one on my home NAS. The Tidal version was still more forward with a bit of excess edge definition and sibilance, but now not entirely unpleasant. It was even kind of fun. My 14-year-old daughter liked the Tidal version more, but I still thought the NAS version had fewer digital artifacts and was better overall.

Certainly, this track was rendered arrestingly well via the KR amps. The room-filling soundstage was intoxicating, with separated sounds emerging in a self-energized way from their defined positions on the stage. The presentation put me in mind of the solidity of those floating blobs in a lava lamp, with their fascinating, inexorable movements. The speakers didn't disappear completely, but the apparent source of each sound was convincingly unrelated to the position of the actual speakers.

On this track, there is a low-level background piano riff. It projected so far forward of the rest of the soundstage that it sounded like it was coming from my lap. I thought the cell phone on my belt was ringing and actually pulled it out to check. For the hidden-detail aficionados among you, at one point, as Simon sings "There's nothing to it, nothing to it . . ." he leans back from the microphone to scratch his chin. Both the lean and the scratch were clearly audible. It sounded to me like two-days' beard growth. If it had been three, the KRs would have revealed it.

In the finale of the song, Simon pulls a slap note hard on his guitar: sharp as a whip, no distortion, perfectly timed, and startlingly loud. I've heard the effect of sounds leaping out of speakers before. This time, the slap leapt out of the empty air between the speakers -- a very satisfying illusion. What the KR amps did here was take a laid-back acoustic track I've always loved and revealed its full tour de force glory, with stunning accuracy, great rhythmic flow and strong emotional involvement.

I wanted a better test of low- and high-frequency extension, so I turned to Patricia Barber's "A Taste of Honey" from the album Café Blue [EMI B00000K3BF]. This track sports a huge, deep bass line. With the VA910s, it rose up from the floor like a seismic phenomenon, perfectly controlled. The Lansches don't normally plumb the deepest depths, but here was tremendous bass fullness that left me wanting for nothing.

Part of the way through this track, maracas come in, which the VA910s rendered with unsafe sharpness. You could "see" the maracas physically moving back and forth in the soundstage as they were shaken by the player. It was almost too real. Emotionally, this track, which is one I had never really noticed before the KRs (in the "before KR" (BKR) era, one might say), was hauntingly beautiful. Barber's voice, not always my favorite, had a beguiling quality, like absinthe -- or what I imagine absinthe must be like: bittersweet, undertones of green anise, and a premonition of dangerous intoxication.

I went through a variety of different genres. Aggressive synthesizer bass? No problem. Pop music was a pleasant surprise -- not at all unlistenable. Bob Marley sounded terrific. Justin Bieber's "Love Yourself" sounded great, as did the various rap tracks my daughter's boyfriend played. Blues were right on. The VA910s are truly all purpose, non-fatiguing amps, which is rather a rarity from such high-resolution equipment. Usually, there's a tradeoff. If your equipment lets you discern the microstructure of a fine acoustic recording, then heavy-handed pop compression effects may burn your ears off. Not so with the VA910s.

The KR amps gave perhaps the best rendition I've heard of one of my favorite classical recordings, Pablo Casals playing the Bach Cello suites [EMI B0032HKEMW]. This recording is old and scratchy, but has superlative emotional content befitting Casals' reputation. The KRs nailed it. The room filling effect of the KR system caused Casal's solo cello to ring out like a full orchestra, savagely intense one moment, yet lyrical and delicate the next. A great performance to enjoy with some bourbon after the family has gone to bed.

Working through the various associated components over time gave me a fairly confident sense of what the KRs were capable of, and also their limitations. I was able to play them at my preferred louder-than-normal, critical-listening volumes most of the time, but I had to back off the volume once or twice because of clipping. These amps can run out of power at high volumes or with demanding speaker loads. Perhaps as a consequence or lack of headroom, the dynamics, while very good, are not world-class. As my experience through the Mezzo Utopias showed, the KRs can sound hard with the wrong speakers. Highly resolving speakers with smaller woofers are likely to work best.

As a primary trait, the VA910s were tremendously, and rather beautifully, accurate. They were liquid, even "wet"-sounding, but not relaxed or laid-back. Images were naturally focused, not laser-focused. The amps were balanced and continuous top to bottom, very quiet, and they didn't make any gross errors such as blurring, adding sibilance or exaggerating transients in any part of the spectrum. They did not "bloom," nor was the presentation illuminated or glowing. Warmth or atmosphere in the recording, if present, came through in full measure.

A nice property of these amps, which I appreciated given some of my previous experiences with what you might call super gear, was that they did not force themselves on me. The more I paid attention, the more I was rewarded with detail and emotion. If I was busy with something else, they politely populated the background with well-resolved sound. They did not grab me by the face and make me pay attention.

The VA910 midrange had lovely, emotionally significant accuracy, but it was not as magical as that of a a SET amp, nor did the VA910s bring out the inner harmonic structure of music in the way triodes or OTL amplifiers can. I had no complaints with their bass, which was full and nimble. The upper end of the frequency spectrum, however, was not quite as extended as it could be, with a little less airiness or openness in the upper reaches than I would preferred.

For comparison, I swapped a pair of Lamm M1.2 Reference monoblocks into the same system (Lansche 5.1 speakers and Coincident preamp). The Lamms are also hybrids, but in the other, more usual way, with a (one) tube input stage and solid-state output stage. The M1.2s are a 30-year-old design with an impeccable worldwide reputation and are significantly more expensive, at about $27,000/pair, than the KR amps. Interestingly, given their solid-state output, they have lower rated power, specified by Lamm as 110 watts each into 8 ohms. In the real world, speakers have variable loads, significant portions of which are often 4 ohms and below, where the M1.2s have about twice the power of the VA910s, and even more in the bass.

What I heard was this: the bass of the Lamms was fuller and faster, and there was more power overall and more dynamic headroom. Where the Lamms fell down was a flatness in the midrange and above, and a signature in those regions in the direction of transistors -- a shut-in, tinny quality. Relative to the KR amps, vocals through the Lamms were distant and less voluptuous, and they could not come close to eliciting the profound emotional effects that the KRs drew from me with ease. Perhaps a true bass head might favor the Lamms over the KRs, but a true bass head wouldn't buy either of these amps.

I realize that these comments could raise the ire of Lamm adherents, so I went back and forth a couple of times on different days and confirmed them. A word of caution to reviewer-curious audiophiles: flaws, once heard, cannot be unheard. Now I hear the Lamms' flaws, even when using them for casual home-theater listening. Damn. Let it suffice to say I'd choose the KRs over the Lamms, no contest.

If it's not already obvious, I'm quite impressed with the VA910 monoblocks. The usual push-pull, four-tube amplifier has, in general, very pedestrian sonics compared to these from KR Audio. How in the world do they do it? These no-hassle tube monoblocks with XLR input just work. The incredibly accurate and emotionally involving sonics have the solid three-dimensionality, huge soundstage, and high resolution and transparency that I call the KR Audio house sound. They have that sound despite the fact that they are push-pull, class-AB amplifiers rather than SETs. They outclassed the more expensive Lamm M1.2s in a direct comparison. From memory, these KRs would also have beaten the much pricier solid-state Linn Klimax Solo monoblocks I used to own. Again from memory, my Joule Electra VZN220 OTL monoblocks were better in some ways, with more airiness and inner harmonic detail, but the Joule amps are impractical and finicky space heaters that require two power cords each and would be more than twice the price of the VA910s if they were still made, which they are not.

My final word is that the KR Audio VA910 monoblocks outclass more expensive competition both in price and performance with no fuss and a sense of high reliability. They are not what most would call inexpensive, but they offer world-class sound at something of a budget-conscious price. I cannot speak for everything on the market, but I would not be surprised to find that the VA910s surpass all comers at their power output and price.

But regardless of power and price, these are emotionally involving, superbly engineered, aesthetically understated monoblocks that are unconditionally compatible with all types of music -- beauty and truth in equal parts.

Price: $16,500 per pair.
Warranty: Five years parts and labor.

KR Audio Electronics SRO
Nademlejnska 1/600
198 00 Prague 9
Hloubetin, Czech Republic

Associated Equipment

Digital: Linn Klimax DS/2 and DS/4 Katalyst renderers, QNAP TVS-463 NAS drive ("Golden cloud”, 16GB RAM, 2TB solid-state Samsung Evo drive) running Linn Kazoo music-server software, Tidal subscription music service, Apple AirPort Extreme home WiFi network to Apple Time capsule (configured as a wireless network extender in bridge mode), generic Ethernet cable from Time Capsule to Linn renderer (hardly any dropouts!).

Preamps: Coincident Speaker Technology Statement, KR Audio P130.

Amplifiers: Lamm M1.2 Reference monoblocks.

Speakers: JMlab Mezzo Utopia, Lansche 5.1.

Cables: Coincident Speaker Technology CST Extreme power cords, XLR interconnects and speaker cables.

Power conditioning and distribution: None. All AC power comes directly from the wall.