The single-ended triode (SET) amplifier enjoyed a fairly brief surge in popularity several years ago, but then audiophiles rediscovered facts that had become obvious in the 1920s and ’30s: SETs just didn’t have enough power to drive most speakers. So push-pull amplifiers again became the standard, and SETs dwindled in popularity. But some companies found the SET sound so beguiling that they tried to overcome the technology’s power deficit. Their success has been mixed. Several models with more power than the early SET amps were developed, but the most powerful of these still produced little more than 50Wpc, and were typically big, heavy, and expensive.
It’s not surprising that KR Audio, in the Czech Republic, has continued to design and make higher-powered SET amps. Originally, KRA manufactured tubes; specifically, power triodes designed to be used in SET amps. It was a logical progression for KRA to build a line of amplifiers that could use their tubes -- such as the integrated amplifier reviewed here.
KR Audio’s VA340 Mk.II integrated amplifier ($9750 USD) certainly looks impressive. It measures 21”W x 10”H by 16.3”D (535 x 255 x 415mm) and weighs 79.4 pounds (36kg). That considerable width means it won’t fit in many equipment racks. A top plate of polished stainless steel is surrounded by a faceplate, rear panel, and side heatsinks, all black. Rising from the top plate are: a wide cover for the power transformer; two tall, hexagonal output transformers; and a protective, black-grilled tower for each of the two output tubes. Those tubes are KRA’s own KR300BXLS triodes, which have a claimed output of 20W RMS per channel at 3% total harmonic distortion. Caution: These are not standard 300B tubes, but a special high-power version. If you use standard 300Bs in the VA340 Mk.II, they’ll probably go up in smoke. KRA’s KR842VHD tube will also work in the VA340 Mk.II. Internally identical to the KR300BXLS, the KR842VHD has a sleeker glass envelope, which makes it run a bit hotter.
Unusually for a SET amp, the VA340 Mk.II uses JFET transistors for the input and MOSFETs for the driver circuits. The front end is passive, with a motor-driven, remote-controlled volume potentiometer made by Alps. The bandwidth is specified as 20Hz-20kHz, -3dB, and the review sample’s single pair of output jacks were set for speakers with an impedance of 8 ohms. The sensitivity of the four unbalanced inputs is 0.75V RMS for full power output, and the input impedance is 47k ohms, which any reasonable source component should find easy to drive. As in most SET amps, no feedback is used, and the damping factor is 2.8 -- ideal for highly sensitive horn speakers such as my Affirm Audio Luminations, which are pretty well self-damped.
A basic remote control lets you select the input and set the volume level. It also puts the VA340 in standby mode, which keeps the solid-state circuits powered up but shuts down the tubes. Since replacement tubes cost $1109.81/pair, it’s a really good idea to turn them off when the amplifier isn’t being used. When a tube does fail, it’s nice to know that you won’t have to adjust the bias current for the replacement -- a microprocessor continually monitors and adjusts tube bias for best performance. KRA says that their tubes typically last around 5000 hours -- quite respectable for output triodes. Heck, it’s respectable for any output tube.
KRA revised the VA340 to Mk.II status in 2011. The changes include a new power supply, an improved power transformer, and better output transformers, which improve the frequency response and signal/noise ratio.
Anytime you consider buying a component from another country, you should investigate its service facilities in your country. Not that the VA340 Mk.II requires much service, but if it ever does, you don’t want to have to ship it back to Prague. I was pleased to find that KRA has five service facilities in the US. I might wish for a longer warranty than the two years KRA offers, but on the other hand, the KR300BXLS tubes are warranted for 12 months, which seems fitting for such expensive tubes.
Setup and use
I’ve always thought that reviewers who described in detail a component’s packaging are attempting to pad out their reviews, but KR Audio’s shipping process is so different it merits some description. Each amplifier arrives in a Pelican shipping case -- big, heavy, enormously strong cases that are used to ship the world’s most delicate gear, and that cost several thousand dollars apiece. When you buy a KRA amplifier, you put down a deposit of $350, the amp is shipped to you, and then you return the case. When KRA receives the returned case, your deposit is refunded. You don’t have to store the massive case in your garage, or find that your better half has disposed of it in a house-cleaning spasm.
Sure enough, the VA340 Mk.II was too big to fit in my equipment rack -- the problem wasn’t its width, but its height. Even the 10” gaps between the shelves of my Billy Bags rack wouldn’t let me squeeze in the VA340, so I placed it on a very sturdy, solid-wood table. Purist Audio Design Venustas unbalanced interconnects connected my Audio Research DAC8’s output to one of the VA340’s inputs, and Clarity Cable’s Organic speaker cables linked the VA340 to my speakers. A Purist Venustas power cord provided AC power.
The review sample had already seen lots of use in shows and at a dealer, so it didn’t need a long break-in; but, like most components, it benefited from warming up overnight to recover from its trip to my listening room. After that, the always-on solid-state circuitry made warm-up from standby fairly short: 15-20 minutes. After using amps with 845 tubes, which radiate intense heat to produce about 25W of SET power, I expected the same from the VA340’s KR300BXLS tubes; but while still running hot, they ran much cooler than the 845s. (KRA estimates an upper limit of 40°C, or 104°F.)
The VA340’s remote control performed its simple functions free of any quirks. The reed-relay input selector cycled sequentially through its four inputs, a small light above each selector button on the front panel indicating when it had been engaged. The inputs aren’t labeled; you have to remember what’s plugged into each position -- no big deal. The input selector on the remote is labeled Channel; a strange choice, but easy to figure out and use. The motorized volume control operated smoothly, and the speed of adjustment was a perfect compromise between fine and rapid adjustment.
All inputs are unbalanced WBT RCA jacks, as is the Record Out jack. I wasn’t aware that many folks still record from their amplifiers, but if you do, the VA340 Mk.II makes it easy. Optional Tape In and Preamp Out jacks can be ordered if you need them. I’d opt for Preamp Outs to drive my powered subwoofers. As I do for all amplifier reviews, I disconnected the subwoofers so that I could evaluate the KRA’s bass performance.
The VA340 Mk.II was very quiet -- no hum or hiss, only a very low thump when the amp was turned on. The lack of noise let lots of detail emerge from the proverbial pitch-black background.
I wished for a few additional features: a balance control (recordings aren’t always perfectly balanced, and precisely balanced channels are necessary for optimal soundstaging), and a Mute button on the remote (really handy when the phone rings).
A game I play with myself is to characterize any device I’m reviewing with a single word. For the KR Audio VA340 Mk.II, that word is muscular, for two reasons: the amp’s very strong dynamic contrasts, and its unusually weighty midbass. Sometimes SET amps can sound anemic, limited by their low power outputs and high distortion. The VA340 Mk.II was anything but -- its sound was amazingly robust, with tonality so dense it seemed almost chunky, with reach-out-and-touch-it vocal and instrumental textures, and thunderous, unstrained climaxes. It was particularly strong in the midbass, which forms the foundation for much music. Many amplifiers seem lean in the midbass, but most music isn’t.
The VA340 Mk.II’s bass went much deeper than usual, and its impact was at first startling. The first amp I used with my Affirm Audio Lumination horn speakers was an Art Audio PX-25 SET, also powered by KRA tubes. It sounded great within its power limits, but those limits imposed some minor listening restrictions. The more-than-three-times-as-powerful VA340 Mk.II also had limits, but they exceeded even my volume preferences, which are rather high. The KRA’s distortion, specified as 3% at full power, is low for a SET amp, whose distortion specs are often as high as 10%. I can usually hear harmonic distortion of a few percent, but heard none from the VA340 Mk.II.
SET amplifiers sometimes suffer not only from limited power, but limited frequency extension as well. Not the VA340 Mk.II. I’ve already described its unusually powerful and extended bass response, but its treble was equally extended. One of my favorite tunes for evaluating treble extension is “The Panther,” from Jennifer Warnes’s The Well (CD, Sin-Drome SD8960); the track’s opening percussion instruments have lots of treble energy. The VA340 had full extension in the highs, displaying excellent detail and air.
SETs are often praised for the palpability of their soundstage, and the VA340 Mk.II lived up to that reputation. The soundstage of the Tallis Scholars’ recording of Allegri’s Miserere mei Deus (24-bit/96kHz FLAC, Gimell) was unusually focused, its depth especially well defined. I find that high-resolution recordings often have well-defined soundstages, and this one is a good example. The voices of the singers, even those in the solo group well behind the main chorus, had tons of detail. Some amplifiers flatten the depth in this recording, or eliminate the resonance within the recording venue. Again, not the VA340 Mk.II.
The First Watt J2 power amplifier is rated at 25Wpc into 8 ohms, close to the spec of the KRA VA340 Mk.II; both are fully balanced. Unusually for a solid-state amp, the First Watt’s output stage is single-ended -- unlike in a push-pull circuit, its output transistors amplify the entire waveform. That was about the extent of the amps’ similarities, however. The J2’s circuit includes only JFET transistors, no tubes, and it's strictly a power amplifier -- I used my Audio Research LS27 line stage to control volume and input selection, connected to the First Watt with Clarity Cable's Organic balanced interconnects. The combined price of the First Watt, ARC line stage, and interconnects was $12,895 -- significantly more than the VA340’s $9750. The KRA also required only one shelf, though that shelf must be wide, tall, and sturdy.
The First Watt J2 is the all-time champion amplifier for bass extension in my system, but since reviewing it last year I’ve discovered that using a Purist Audio Design Venustas power cord produces a smidgen more weight, fleshing out a slightly lean midbass. So the First Watt equaled the bass of the KRA VA340 Mk.II in terms of weight, and even went a bit lower -- and both amps had me occasionally asking myself if I really needed a subwoofer. The Purist cord also eliminated a tiny bit of dynamic reticence, making the sound more robust. I’d used the very same cord with the VA340 Mk.II, so both amps benefited from its support.
Unlike many SET amps, the First Watt has very little intrinsic distortion (a claimed 0.03%), and has a purity of sound that I’ve found unique among SETs. This, coupled with an extended treble, makes its sound quite gorgeous but not at all clinical. With “The Panther,” the treble was extended but not at all peaky, with more high-frequency detail than I usually hear.
Soundstaging was spectacular. With Allegri’s Miserere, I could discern the vocal characteristics of the soloist and foreground choral group, as well as the group of soloists in the background as they soared up to high C (well, at least the soprano did). The reverberant field in which the rear soloist group is immersed was particularly well defined. Both the First Watt and the KRA produced an exemplary soundstage.
The First Watt had plenty of dynamic punch, but the VA340 Mk.II surpassed it, if only slightly, in dynamic performance, sounding more powerful than its rated output.
KR Audio’s VA340 Mk.II was as notable for what it didn’t do as for what it did. Unlike many SET amplifiers, it didn’t have bandwidth limitations, high levels of distortion, or a tiny output wattage measured in a single digit. However, although it produced a very healthy amount of power for a SET amp, it’s still relatively low powered, which will restrict which speakers it can be used with. Big and heavy, it may not fit in your equipment rack. It’s also visually imposing, although some audio nutcases (such as yours truly) may think that an advantage; if they spend $9750 on an amplifier, it doggone well better impress their friends! But if your financial and space budgets will accommodate the VA340 Mk.II, it can reward you with sound that’s spectacular for any price and power output.
The VA340 Mk.II integrated amplifier was one of the best-sounding amplifiers I’ve heard in my system. Powerful yet delicate, it had a complex tonal palette and that legendary SET palpability. It doesn’t have a lot of features, but it has the ones that matter most. I think it looks great, and it’s built like the proverbial brick outhouse. Distortion is audibly low, and its frequency response is extended at both ends of the audioband. If your speakers can work with the VA340’s relatively low power output, it deserves a spot on your must-audition list.
For a while, I seriously planned to purchase the review sample -- it’s that good. But I came to realize that my reviewing duties require a separate amp and line stage, so I reluctantly decided to pass. Still -- highly recommended, and a Select Component.
. . . Vade Forrester
- Speakers -- Affirm Audio Lumination speakers, JL Audio Fathom f110 subwoofers
- Amplifiers -- Audio Research VS115, First Watt J2, Art Audio PX25
- Preamplifier -- Audio Research LS27
- Digital sources -- Hewlett-Packard dv7-3188cl laptop computer running 64-bit Windows 7 Home Premium, foobar2000, and JRiver Media Center; Auraliti PK100 music player; Audio Research DAC8 D/A converter
- Interconnects -- Clarity Cable Organic, Audience Au24e
- Speaker cables -- Clarity Cable Organic
- Power cords -- Purist Audio Design Venustas, Clarity Cable Vortex, Audience powerChord e
- Digital cables -- WireWorld Gold Starlight 6 S/PDIF, AudioQuest Diamond and Coffee USB
KR Audio VA340 Mk.II Integrated Amplifier
Price: $9750 USD.
Warranty:Two years parts and labor; one year, tubes.
KR Audio Electronics sro
198 00 Prague 9
Fax: +420 281864343
19593 Roanoke Rd.
Apple Valley, CA 92307
Phone: (760) 490-2410