While some companies come and go, there are a few that come on the scene and then proceed to go, go, go! Balanced Audio Technology (BAT) certainly fits the latter category. I can’t recall any other company that made their initial appearance with as much splash as BAT did at the ‘95 WCES and subsequently went on to display such remarkable growth within the industry. Both of their debut products were of the tube persuasion and used balanced topology, of course: The VK-60, a 60-wpc power amplifier, and the VK-5 preamp. Today, their lineup spans both tube and solid-state designs and is approaching 10 models deep.
Balanced Audio Technology VK-500 amplifier, $4,950.00. Balanced Audio Technology, 800 First State Blvd., Wilmington, DE 19804; phone 302/999-8855; FAX 302/999-8818.
ASSOCIATED EQUIPMENT
Basis Gold Standard Debut turntable; Air Tangent tonearm; Clearaudio Accurate cartridge; Krell Reference phono stage and power supply; Jeff Rowland Design Group Synergy preamp; Wadia Model 7 CD transport; Museatex BIDAT D/A converter; Townshend Seismic Sink; Tara Labs Decade cables, and Paragon Regent, Celestion SL-600, Platinum Reference 1, Gershman Avant Garde, and Sony SS-9 speakers.
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BAT was formed by two partners: Victor Khomenko, who is the designer of the products, and Steve Bednarski, who does the marketing. That they are committed, is obvious. Even though both of the principals started BAT out on a part-time basis, they now have quit their very desirable normal employment at an exalted company like Hewlett-Packard and have been pursuing the amplifier business on a full-time basis for some time now. Geoffrey Poor has recenlty joined the two other principles to add his skills as Director of Sales.
BAT's VK-60 auto-bias system will allow you to forget about making this regular tune-up.
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BAT products have done very well on the review scene, with high praise being doled out consistently by a number of publications. Just recently, in TAV’s Vol. II, No. 5, our own Bill Wells found the VK-5 preamp very much to his liking. Since my predilection is for a lot of power (single-digit power ratings leave me cold), my ears perked up when Victor decided to configure the VK-60 stereo model into a 120-watt monoblock.
And what a beautiful sight two of these beauties make. First off, there are a couple of very useful ergonomic features that fall into our laps. For example, each monoblock comes with two inputs since both XLR input connectors of the stereo version are retained. Except that for the monos, they appear wired in parallel. This is very handy when you want to bi-amplify, since the need to search out Y-connectors is eliminated. All you do now is run your input cable for one channel into the input of first amplifier and, using a regular cable, daisy-chain the second amp to the other input of the first unit. On the output side, the two sets of output connectors used in the stereo version are also retained but wired in parallel, thus making bi-wiring ever so much more convenient. Instead of eliminating parts, they put them to good use. In my book, these are more than mere nice touches. It is also a confirmation of a thoughtful engineering approach. Which brings me to a recapitulation of some of the original features of the VK-60 that made this product so special and user friendly.
Once you get the BAT VK-60, you can forget about bias problems. Auto-bias is the name of the game and is confirmed by a green LED in front of each output tube and visible from the top of the chassis. If it’s lit, the unit’s biased. Should the LED not be lit, check the fuse, which is accessible from the corresponding opening in the bottom cover plate of the unit. These openings are a feature that I expected as minimum from BAT, so they really gain no points for that from me. Had they made the fuse accessible from the top, then I really would be doing cartwheels, though they do supply several fuses with each unit, just to be on the safe side. As for me, I had only a very rare occasions to change fuses, which were brought about by putting too many unreasonable demands on the output capability of the amp.
The only control is a power switch on the a.c. cord, and you need select only your speaker impedances.
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For those unfamiliar with the BAT VK-60, a summary of the main design features is included as a sidebar to this review. Basically, the BAT monoblock consists of wiring both 60-watt stereo channels of the VK-60 in parallel to produce a 120-watt mono-output amplifier. Being that the output is transformer-coupled, these 120 watts are available as long as the proper output taps are selected to match the nominal speaker impedance presented to the amplifier.
 It should be of interest that no negative feedback is employed in the VK-60. Only plate-loaded triode circuitry appears throughout (that means there are no cathode followers), with nothing but custom oil-filled capacitors in the signal path, and the amps are fully compatible with single-ended preamplifiers. Even though only balanced inputs are available on certain BAT products, a set of adapters are provided for applications where single-ended preamps appear.
Single-ended triode fans should rejoice, since this is a single-ended output except that it is in a bridged configuration. According to BAT, this provides the best of the push-pull and thesingle-ended worlds. The output transformers are unique since they are toroidal, without an air gap, and use a low transformation ratio to produce a broad-band design where the -3 dB points cover the range of 7 Hz to 70 kHz. Since each channel of the VK-60 uses a separate potted output transformer and the output windings are wired in parallel in the monos, the output impedance is cut in half in the monoblock configuration.
The set of monoblocks is very impressive physically.
No way they can go unnoticed. Each measures some 17 inches wide, 24 inches deep, and 8 inches high, so two of them take up quite a bit of floor-space, and the 85-lb. weight (per monoblock) demands careful consideration when positioning them anywhere above floor level. Three transformer modules sit in the rear of the chassis, while a total of 12 tubes occupy the front of it. Out of the 12 tubes, eight are 6SN7s and the other four are the physically imposing 6C33. It surely is a sight to behold when two of these monoblocks are aglow in full bloom, ready and able to do what they do best.
But as imposing as these BATs amps may appear, operating these beauties is a snap. The only control is an "on/off" power switch located on the rear of the chassis right next to the power cord. Distributed along the rest of the rear plate are two groups of four metal binding posts, which accommodate a wide variety of speaker impedances, with three ranges indicated on the back plate. As I mentioned, bi-wiring is most conveniently implemented. What is not obvious, however, is the added flexibility available to the user. In order to please the wide variety of user demands, it is now possible to separately match the woofer and mid and high frequency sections of loudspeakers to individual taps to provide the best results in the listener’s environment. That means possibly running the bass and upper frequency speaker sections from different output taps.
Along with the power switch on the rear of the unit, there is another fuse in the a.c. line circuit, as well as a power-on indicator, a blue LED, in the center of the front chassis plate. Positioned slightly below the top chassis plate, and directly in front of the corresponding output tube, are four bias indicator LEDs. They are intended to be viewed from the top of the amp to make sure the bias is on. That’s it, a plug-and-play design in the true sense.
I really enjoyed the convenience of having the auto-bias feature. Remember, this circuit not only keeps the tubes biased optimally during playback, but also while the amp is going through the initial warming up period. Not having to wait for the bias to settle in brings this amp up to speed that much more quickly. It’s soothing for our impatient moods, and it is good for the tubes since listening can commence while still warming up.
Switching between higher power mono output and standard stereo operation is easy to accomplish.
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Please note that a VK-60 can be easily converted to a monoblock and vice versa. One can start out with a standard stereo VK-60 and then later do the conversion and add another amplifier to double up on the power in each channel. As I mentioned, this is an all-triode design, and since the BAT principals are confirmed believers in the balanced approach, the design is fully differential from input to output.
Of course, issues other than mere faith are important when it comes to deciding on the balanced topology approach. Let’s face it, in our world of e.m.i. and r.f.i., decent hi-fi is seriously compromised without a balanced approach. It’s not a matter of a higher parts count nor an alleged increase in circuit complexity. It has to do with the fact that a balanced circuit responds to a differential input. Or, an output will result only if the two input terminals are at a different potential with respect to the other.
A single-ended signal responds to a difference between the input terminal and ground. In a differential circuit, interference will affect both inputs equally and therefore will not result in a change in the output, while the same interference will affect the output of a single-ended circuit since the input responds to a change in potential with respect to ground. Even worse things happen when the ground is contaminated in a single-ended circuit because the reference point is now shifting and that appears to the circuit as a change of input potential. A properly executed differential circuit rejects signals that appear simultaneously at each of the two input terminals, and this ability been quantified into a well-known parameter for measuring the circuit’s ability to ignore non-differential signals. It’s called the common mode rejection ratio or CMR.
BAT's marvelous midrange presets a harmonic richness that is nothing but spectacular.
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One often hears the argument for using differential circuitry only when long cables are involved but it is not applicable. Today’s rampant contamination sources are pervasive, and differential circuitry is bound to help in our goal of keeping all of the frail musicality in the signal intact. However, like anything else, differential topology is not a boon unless it is properly implemented.
Listening
Once you have inserted the tubes, it’s plug and play. Plug in the a.c. power cord and play the music. And does it ever play the music, and the tunes and the rhythms and the melodies! This BAT proceeded to deliver delicately delineated harmonic riches and unraveled musical complexities with an unusual deftness and finesse. However different the backgrounds of the three partners may be, their products do speak the one common language we all love and understand . . . and that’s music!
As hard as it may be for some of you to understand, I have an on-going love-hate relationship with tubes. However, the BAT monoblocks have placed me currently a long way over on the love side, making me forget my misgivings of the tube situation.
In short, my hesitations had to do with truncated as well as muddled bass response and an abbreviated high-frequency extension. The BAT monoblocks practically alleviate all of my reservations, more so in the upper reaches than in the lower regions.
If you are miffed at me for not succumbing unconditionally to the charms of the BAT monos, then you are living in a world of illusions. The real world is far from perfect, and within that context, the BATs are doing great. Were these amps the answers to all my prayers, then Victor, Steve, and Geoff would be filthy rich by now and world famous to boot.
What the BAT monos do, however, is to tighten up the bass considerably and render a high frequency response that is nothing short of fabulous. The final result is a spectral response that is balanced and musically satisfying. Within the context of reproduced music, these amplifiers do an outstanding job.
As expected, the BAT’s marvelous midrange always presents itself with very little room for criticism. The harmonic richness is nothing but spectacular. Violas, cellos and bassoons are rendered stunningly captivating, keeping the listener enraptured for hours on end. It matters not whether strings are bowed or plucked, appear en masse or solo, the ability of the BAT monos to resolve and reveal delicate details is absolutely stunning. I simply find myself playing much more classical music, small and large scale, far more often with the BATs in the system than I can recall doing in previous auditions.
All my previous experiences with tube power amps have left me with an impression of darkness and constriction, despite however open the midrange presentation was. Not enough sparkle and life. Well, the BAT monos do away with these doldrums. Openness and transparency, speed and immediacy . . . that’s what I hear from this pair of BATs. Musical enjoyment radiates with a sense of ease and distinct lack of restraint. It seems that the BATs get out of the way and provide a very unobstructed venue for the musical values to materialize. Certainly, it is not a case of smoothing off the essential transient components and making things nice and smooth and polite. Far from it. Dynamics are remarkably forceful, and they come with inner detailing that is simply beguiling. This is a product that makes its presence felt in the most subtle and desirable way. Its presence is affirmed by its ability to stay out of the way of the music. It is present because it is absent!
The VK-60 is one great amplifier, with an ability to stay out of the way of the music.
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To be sure, this is one great amplifier. But I would not have been able to unravel its full capabilities without some similarly refined equipment surrounding the BATs. The Museatex BIDAT D/A by Ed Meitner has benefited from a several recent revamping sessions and it has gotten to where its performance simply sends shivers up and down my spine with is uncanny ability to supply musically satisfying and sonically credible inputs for the amplifiers. This has not been a process of tweaking but a re-examination of the design and followed up with attendant well thought-out remedies. I want to emphasize that whenever I critically evaluate amplifiers, the BIDAT feeds the amplifiers directly, eliminating the possibility of a preamp cluttering up the sound of the system with a contribution of its own.
The DECADE cables from TARA Labs have also managed to keep me overwhelmed with their consistent ability to the keep the signal as uncolored as possible. And its not for lack of trying. Having tried a number of other highly regarded cable products over the years, I am left with the impression that these products did indeed deserve the praise that they had received, but the DECADE series consistently was the preferred choice. In the end, TARA Lab cables were more transparent, exhibit a remarkable spectral balance, and have an ability to maximize the transfer of the signal subtleties between the system components while keeping themselves very unobtrusive.
I feel very confident in praising the BAT monos because it was in the speaker area that these amps could be subjected to difficult loads from a very wide variety of models. A list consisting of Paragon Regents, Celestion SL-600s, Platinum Reference 1, Gershman Avant Gardes, and Sony SS-9s represents about as much variety as can be expected for a reviewer to have available for an amplifier review.
Conclusion
I must confess that I will always gravitate to a product that appears to have been based on sound engineering as opposed to an approach that implies the discovery of some proprietary magical principle or topology. BAT is about as straightforward in their engineering presentation as can be expected. Add to that their ability to produce products that have the high-end community abuzz, and they are people who deserve lots of recognition.
My experience with the BAT monoblocks has been thoroughly enjoyable and eminently satisfying. These amplifiers are capable of drawing the listener into the music in a mesmerizing manner with their ability to provide a signal path that does the music full justice. They have an ability to stay true to the harmonic integrity of each instrument, which to me is a most important ingredient in music reproduction.
A power amplifier is an irreplaceable component in today’s technology. While we have a choice in our input sources and we can eliminate a preamp under several scenarios, a power amp is a system component we are stuck with. As such, getting the proper amp is a very important consideration in assembling a top-drawer system.
The BAT monoblocks deserve your very highest consideration in your search for a satisfying power amplifier. My experience with them convinced me that a very high level performance is there for your taking.
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The main power tube used in the BAT VK-60 is the 6C33C-B, a high-current, low-impedance triode design originally used in the power supplies of the Russian MIG fighters, where it had to withstand forces up to 7 Gs. The tube’s current delivery is exceptionally high, with more than 10 times the current capability of either the 6550s or KT-88s commonly found in tube amplifier designs. Four of these are used in each amp, along with eight 6SN7s.
The VK-60 uses a novel zero-feedback, single-ended bridge design. In contrast, most tube amps of this power output ordinarily use 6550s in push-pull mode, and very often suffer from crossover distortion or sound harsh in the upper registers. The VKN-60 is actually four single-ended amps within a single chassis, one for each phase of the balanced signal. To cancel d.c., the outputs of each pair of positive and negative legs of these single-ended amps are bridged prior to the output transformer. This eliminates the potentially large d.c. component and its accompanying core saturation, but requires a floating power supply for each of the four single-ended subcircuits, thus making the overall design more expensive.
One of the most interesting aspects of the VK60’s design is its automatic biasing circuit, which keeps each individual tube at its correct bias level. By compensating for warm-up, aging, and other sorts of tube variation, as well as fluctuations in a.c. line voltage, the VK-60’s auto-bias circuit keeps the owner from having to make potentially tricky and difficult adjustments requiring a digital voltmeter, small screwdriver, and a high level of patience.
The unit which I am reviewing here is the VK-60 monoblock conversion which is accomplished by simply paralleling the inputs and outputs of the amp. This brings the power output up to 120 watts per channel and improves the output impedance by a factor of two. In fact, any number of VK-60s can be paralleled together up to the limits of your house wiring, heat tolerance, and wallet thickness.