Why does BAT make both solid-state and vacuum tube electronics?

Just as there can't be one best wine for all meals, there isn't one best amplifier or preamplifier for all music systems and tastes. We believe that properly designed vacuum tube and solid-state electronics can and should coexist and complement each other, very much like red and white wines complement fine cuisine and coexist in the real world. BAT's mission is to give our customers choices that fit their lifestyles, budgets, and system needs. Our goal is to make a contribution to the art in any product undertaking. BAT's vacuum-tube and solid-state lines have been recognized for such distinctive contributions as automatic biasing (all BAT tube amps), two-stage high-power amplification (VK-255SE & VK-655SE) and the Unistage® signal path (All BAT preamplifiers). We are pleased to offer industry-leading designs in all these areas. Customer response has overwhelmingly supported BAT's multifaceted pursuit of excellence.

Why should I buy from Balanced Audio Technology?

Please read our BAT white paper for more insight into the extraordinary level of development and the meticulous execution that goes into each of our products. Then visit your BAT audio specialist to hear these exciting components in a well-set-up system. The main reason to buy one high-end brand over another should be that it plays music better. We're firmly convinced that you'll hear the difference with BAT. As one satisfied Balanced Audio Technology customer told us: "Your product looks great! When I opened it I came to appreciate that it looks even better on the inside than the outside. After I plugged it in, what impressed me most is that it sounds even better than it looks!"

What cables should I use with my BAT system?

We haven't designed our electronics to work with a particular type or brand of cable. BAT electronics are wonderful at revealing cable differences and at providing a high level of performance with even modestly priced cables. Let past experience, your budget, and your ears be your guide.

Is the requirement for minimum input resistance dictated by the output resistance of your preamps?

No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system). The unusual design of Balanced Audio Technology's preamplifiers allows their gain stages to drive loads with resistance much below what their specified output resistance ratings would imply. For example, the VK-53SE preamplifier can supply a load with 65mA peak current - an amount well beyond that of the great majority of preamplifiers on the market today.

How often will I need to replace tubes in my unit?

We expect the general tube life to be in the four year range. Your tubes may last substantially longer depending upon usage. This is due to low stress factors designed into BAT components and soft start circuits incorporated in them.

Should I consider replacing the stock tubes with "upgraded" models?

We strongly believe that the tubes used in our products offer the best combination of sound quality, reliability, low noise and microphonics. However, there are many other tubes on the market, both new and NOS, that may offer a different sound character when installed in our equipment. The final value judgement regarding the sound quality as a result of such substitutions rests solely with the customer. However, there are certain things to consider. Given the wide diversity of various brands and models, Balanced Audio Technology can't guarantee the final results. Some tubes may not function properly in our equipment. It is always important to work with a vendor who stands behind their product should any problems develop. Finally, any repair work required as result of using tubes models and brands other than those originally specified by BAT would not be covered by warranty.

What makes the BAT electronic shunt volume attenuator so special?

In most preamplifiers the volume control works as the gatekeeper of sound quality. Any damage done to the sound by an improperly implemented volume control will then be further amplified by the gain stage. This is why we had to develop our own solution to this critical function (please see the i-series white paper for more information on this subject). We were not satisfied with the traditional implementations available and undertook a costly but rewarding search. In our opinion, the best way to implement the volume control in a preamplifier is through an electronic shunt attenuator that puts only one high quality resistor in series with the signal. In many traditional implementations there will be dozens or even hundreds of components inserted in the signal path, plus multiple solder joints. A typical integrated circuit (IC) volume control found in many high-end preamplifiers may also place operational amplifiers in series with the signal. This would contradict our philosophy of a short and unobstructed signal path. The low cost of integrated circuit volume controls makes them attractive in low cost products. However, a $5 volume control hardly deserves a place in any true high-end preamplifier.

Why should I be concerned about an integrated circuit volume control at my preamplifier input?

Besides the above-mentioned drawbacks associated with the IC volume control's complexity, they usually also suffer from very limited signal headroom. A typical part in use by some manufacturers will clip the signal as low as 3V. Many of us might recall numerous discussions by leading designers regarding the importance of signal headroom. Put simply, in order for a circuit to deliver low distortion and clear and transparent sound, it must be able to handle a signal with a magnitude many times larger than the normal level encountered in a music program. Many respected designers believe that a circuit must be able to handle a signal of at least 10 to 20 times above its normal value. Some go even further. No one would consider 5% to be acceptable headroom for an audio circuit. The typical audio signal produced by audio sources falls between 1 and 10V. To handle such signals properly, the preamplifier must have an allowable input voltage range of at least 20 to 100V. What happens when you apply the 10V signal to a typical IC volume control with its allowable input range of only 3V? The answer should be obvious. Needless to say, the input voltage range is rarely specified for preamplifiers. A 3V limit should hardly be considered adequate. All Balanced Audio Technology preamplifiers, on the other hand, are capable of handling virtually any input signal magnitude, limited only by power dissipation in the volume attenuator. Input signals as high as 100V or even 200V would not present any problem. When considering a new preamplifier purchase, ask the manufacturer about this important parameter - the allowable input signal range.

Should I use a power conditioner with my BAT equipment?

Balanced Audio Technology first recommends that our equipment be connected directly to a good quality power line. A single dedicated power circuit will usually produce the best result. The presence of electrical noise or common impedance interaction may, in some instances, warrant the use of power filters or conditioners. However, because every system is different, always make sure you try the system both ways - with and without the conditioner, in order to make the proper buying decision. When employing any kind of filter or conditioner, please make sure that BAT preamps, including the VK-P10SE phono-stage, are treated as you would normally treat a power amplifier in terms of power requirements. Some conditioners may have limited current delivery on the "preamplifier" outlets and will not be able to handle the 150 watt requirement or the turn-on transient from our preamplifier's massive power supply.

Should I use separate dedicated power lines to power amplifiers and my source components?

Contrary to popular belief, the answer is most often NO! Every system is different and it is hard to come up with a general rule. However, in order to minimize the chance of ground loop noise and signal degradation, it is advisable to assure that no large voltage differences exist between the chassis of different components in the system. These voltage differences will be more pronounced in a system incorporating several separate power lines. The voltage differences will be higher in the case of longer power lines and stronger current demand by heavy components (i.e. power amplifiers). Usually the safest approach is to run one strong (probably 20A) power line to your listening room and plug all your audio components into it. This approach creates a STAR power distribution system that should be less prone to ground loop problems.

My circuit breaker panel is over seventy feet away from my listening room. The total current draw of my system is above the maximum that a single power line would allow. What should I do?

In many cases the best possible way out of this predicament would be to install a new sub-panel close to your listening room. You must consult your local electrical code and qualified electrician, but usually a new 60A or 100A panel can be installed. Several short (ten feet or so) separate power lines can then be connected to outlets. Use short dedicated lines, (preferably 20A rated), from this new sub-panel to your audio components. Make sure that all audio components are connected to the same phase of the power line. To do this, check the locations of the circuit breakers that protect the power lines used the for audio system. The panel is arranged so that two vertically adjacent breaker positions are the opposite phase. This is so 240V breakers can easily connect to the two phases. So to get two breakers on the same phase, there must be an odd number of positions in between. Horizontally adjacent breakers should be the same phase. Do not be fooled by "tandem" breakers. They have two circuits in the space occupied by a normal single circuit breaker. They are both connected to the same phase and only count as one position.

I am using a combined Audio/Video system and get a lot of ground loop noise. What is the solution?

Very often in such an installation the culprit will be the grounding in the cable TV circuit. The surest way of solving it is by buying a cable TV ground isolation device (transformer) that is available from many high-end dealers.

Balanced Operation

Is there a simple explanation of the difference between single-ended and balanced operation?

In this context, the terms "single-ended" and "balanced" describe the type of electrical interface between components: i.e. preamplifiers and power amplifiers. Single-ended interfaces use a "common" conductor (shield, ground or instrument chassis) as a signal return path. Balanced lines, on the other hand, use two dedicated conductors to provide forward and return paths for signal. The ground connection in balanced configurations is accomplished by means of a third, dedicated, ground conductor. Any two components in your system will, most likely, have a measurable voltage difference between their chassis. When a single-ended cable is connected between these two components, this voltage difference will appear along the common conductor (shield) of the interconnect. As a result, the shield will now carry the parasitic ground noise current between the two chassis. Since the shield is directly in the signal path, the voltage drop along the ground conductor will be combined with the signal that the interconnect carries. The result will be added noise and distortion introduced directly into the signal path. In a balanced system, a separate shield or ground conductor will be used to connect the two chassis together, reducing the voltage difference between them. But the voltage drop across the shield will not add to the signal, because this third conductor does not carry the signal. What flows through the balanced interconnect is a clean signal, separated from extraneous ground current and noise. Additional benefits are derived from the fact that balanced circuits are inherently symmetrical. The balanced nature of the internal circuit greatly reduces transient demand on the component power supply, further improving signal integrity and noise immunity.

What makes the balanced interface superior to a single-ended interface?

The superiority of the balanced interface comes from at least four areas:

  1. Connector quality. This one is probably the easiest to understand. Balanced XLR connectors use large diameter signal pins. They also are superior to the common RCA in that they provide a positive locking action. They incorporate properly designed strain relief as a feature. In the case of an RCA connector, the signal-carrying ground conductor also works as the strain relief - a situation far removed from ideal. Many of us have experienced broken RCA connectors when subjected to lateral forces - including the weight of some high-end interconnects. The high degree of mechanical and electrical integrity makes balanced XLR connectors the natural choice when signal integrity counts.
  2. Balanced interface noise immunity. When discussing different signal interfaces, it is important to evaluate their immunity to various noise sources. One group of these sources is represented by noise currents that flow between different chassis in a system (and between different parts of the same chassis, in fact). We shall call them ground noise sources. The second group includes various external sources that do not have a direct electrical connection to our system, but can affect it through their electromagnetic fields. Items commonly included in this category are various RF sources (radio stations, RF remote control transmitters, etc), magnetic fields (fields commonly found around large power transformers, power lines and home appliances), and electrostatic discharge events. Because of if its three-wire configuration, a balanced interface is substantially more immune to all of the above interference sources. By using balanced interconnects throughout our system, we, therefore, noticeably improve our signal integrity - our music signal is much less affected by extraneous noise.
  3. Internal power supply-gain stage interaction. It has been stated thousands of times before that the power supply has an enormous influence over the resulting sound of a product. With this in mind, we can take two different design approaches. One would be to put very high requirements on the power supply and then hope that it is up to the task. A second approach would be to simply minimize the demand on power supply performance from the start. Single-ended circuits put very high demands on the power supply's ability to keep up with signal-induced current fluctuations. Single-ended signals produce changes in gain stage current that must be accomodated in the power supply. Unless the power supply is capable of coping with large and fast current changes, it will constantly fall behind and the resulting sound will be degraded. Balanced circuits interface with their power supply in a "balanced" fashion. There are two gain stage currents present in the balanced circuit at any time. By the very nature of a balanced circuit, when signal appears at the input, these two currents will change in unison. One will increase, and the other one drop by the same amount. The resulting gain stage current change can be made almost infinitesimally small. In the ideal case, the power supply will not see ANY current fluctuation at all, and its job will become quite easy. This reduced demand not only makes power supply design far more efficient, it improves the performance of the power supply substantially.
  4. Many of us believe that symmetry is good. Balanced gain stages are inherently symmetrical. Little wonder then that many famous designers reached for balanced circuits long before the word "balanced" was used in high-end audio. As long as forty to fifty years ago, when all stereo components contained nothing but RCA connectors, many now classic designs were already completely balanced internally. To work with the RCA interface (the only one available at the time), one input of the balanced circuit was simply grounded. Why would designers use fully balanced internal circuits with RCA jacks for interfaces? The answer is that, even then, many designers believed in the inherent superiority of balanced designs.

Why should I consider buying a balanced component if I have a single-ended system?

There is a growing volume of evidence that a balanced interface offers superior sound quality. More and more companies are adapting it. The balanced interface is becoming the de facto standard for high-end electronics (witness the proliferation of XLR connections on digital converters, power amplifiers, etc.). Today, Balanced Audio Technology's equipment is perfectly compatible with your single-ended system and will most likely yield higher performance than a corresponding single-ended alternative. Tomorrow, if you add a balanced source, preamplifier or power amplifier, your system can take advantage of the benefits of fully balanced signal handling.

Can I easily hook up my single-ended components (i.e. ones with RCA jacks) to Balanced Audio Technology's electronics?

Yes. All Balanced Audio Technology products are designed to work flawlessly with any mix of balanced and single-ended components. Balanced Audio Technology manufactures custom high-quality balanced-to-single-ended adapters for just this purpose. Each adapter is made with a machined virgin Teflon mating shell that connects an XLR front half to a Teflon-insulated RCA jack. Just plug the adapter into the back-panel XLR connection on BAT electronics and you can use the high quality single-ended cable of your choice. No external active converter is required to make this connection. In addition, products such as our VK-33, VK-33SE and VK-42SE already offer RCA jacks on the back-panel for a direct connection to any single-ended component.

Is there going to be any performance degradation in using a mixed balanced/single-ended system?

No. All BAT electronics will work perfectly with any mix of components. However, moving to a fully balanced system will bring additional musical enjoyment.

I've heard that not all units that have XLR jacks are truly balanced components? Can you explain this?

Yes. There are many products on the market that add XLR connectors to an internal single-ended circuit. Such designs, while sporting XLR connectors, don't process the signal in balanced form. It is fair to call such units "pseudo-balanced". Unfortunately, this fact is usually not stated accurately in the company literature for these products.

What differences are heard when moving to a balanced system from a single-ended system?

We have conducted an extensive comparison of Balanced Audio Technology systems operating in both balanced and single-ended modes. The same external components were used as well as the same manufacturer's cables. Consistently, the balanced connection yielded a superior sense of air, more three-dimensional images, and a more clearly defined soundstage. The music was infused with greater life and energy.


Why does Balanced Audio Technology offer a choice of so many phono-preamplifiers?

The VK-P3, VK-P5,  VK-P10, VK-P10SE and VK-P10SE SUPER-PAK cover a broad spectrum of needs for the analog enthusiast both in terms of price points and features. Balanced Audio Technology is dedicated to providing the finest possible reproduction of music in the home and strongly believes that outstanding analog reproduction remains a key element of that commitment.

How do I choose the phono-preamplifier that is right for my system?

The choice between the VK-P3 phono-module and the VK-P5 is easy. The VK-P3 inboard phono-module offers extraordinary performance for either moving-magnet or moving-coil cartridges (and the convenience of a single-box solution for a combined line stage and phono-stage). The VK-P5 is a ten-tube phono stage that moves the listener much closer in performance to the ultimate sound of the VK-P10 series of phono preamplifiers. If you still listen to analog a great deal, but find the VK-P10, VK-P10SE or VK-P10SE SUPER-PAK priced beyond your budget for a phono stage, our recommendation is that you choose the VK-P5. The VK-P10 series is for the analog aficionado who simply wants the best possible reproduction for his or her analog system. They offer unmatched flexibility and a superlative sound that reveals the finest nuance in both recordings and ancillary equipment.

Can you elaborate on the differences between the VK-P5 and VK-P10 series of phono-stages?

The VK-P5 and VK-P10 are based upon the same ten-tube dual-mono circuit. They also use the exact same tubes and the exact same power supply transformers. They are different in that the VK-P10 adds polarity switching, switch selectable step-up transformers, custom oil-capacitors in place of polypropylene parts, and greater power supply energy storage.  As we move up the line, the VK-P10SE completely revises the first gain stage to provide a substantially lower noise floor.  In addition, the VK-P10SE's reconfigured output stage incorporates four high-gain 6C45 tubes to provide even greater dynamics than the already stellar VK-P10 phono stage. Finally, the VK-P10SE SUPER-PAK adds the same second generation oil-filled capacitors used in the REX II preamplifier for its SUPER-PAK based power supply.  THE VK-P10SE SUPER-PAK naturally provides the ultmate in detail retrieval, and provides the greatest air and soundstage dimensionality of all of our phono preamplifiers.

When should I use the step-up transformers in my VK-P10, VK-P10SE or VK-P10SE SUPER-PAK phono preamplifier?

Most customers seem to prefer the direct connection mode (step-up transformers disengaged). In direct mode the VK-P10 series of phono preamplifiers can comfortably handle phono-cartridges with output as low as 0.2 mV. Usually in such a set-up, the input noise of the gain stage will be substantially below the surface noise of even the cleanest records - a good criteria for system noise evaluation. However, for the rare cartridge with very low output (0.2 mV or less), you should try using the built-in step-up transformers to provide higher gain and improved signal-to-noise ratio. Note, however, that these are general rules. In a number of cases, we have found higher output cartridges that sound better with the step-up transformers engaged. We believe that the step-up transformers may offer a synergistic match with some of these cartridges. The net result is that you need to listen to both alternatives to determine which is best for your system.

How do I determine the optimum cartridge loading (both resistance and capacitance)?

As general rule, we recommend that you start with the cartridge manufacturer's recommendation. If a particular cartridge calls for a 47 kΩ resistor and no capacitance, then make this your starting point. There is no risk in experimenting with these settings and engaging for example, 1 kΩ or even 100 Ω load resistors. Usually, cartridges will yield a bit more "air" when loaded with higher value resistors. Engaging additional input capacitance will usually help to tame the rising top end of many moving coil cartridges.


Why has Balanced Audio Technology introduced a new series of transformer-coupled preamplifiers?

Well-designed transformers can come closer to the ideal device model than capacitors.  They also virtually eliminate the traditional problems of capacitor-coupled outputs - their sensitivity to load impedance.  Balanced Audio Technology spent almost three years working with a premier supplier of signal transformers to develop the solution for our unique needs. The result is very rewarding.  In addition to the direct improvement in electrical performance, the VK-33SE, VK-53SE and REX II preamplifiers also demonstare a marked improvement in sonic performance as well.

How do the new transformer-coupled preamplifier models compare sonically with the previous models?

We received an email from one of our long-term customers that sold his VK-52SE preamplifier in order to purchase the VK-53SE transformer-coupled preamp as a replacement. After break-in of the VK-53SE, he remarked as follows:

the thing that makes this preamp [VK-53SE] spectacular is that it sounds... for lack of a better word, incredibly fast. By that I mean to describe the subjective impression that subtle components in the complex waveform seem to be much better discriminated. The primary effects of this are 1) that partials/harmonics in the instrumental tone are more clearly audible, so that timbre is much more individualized and colorful, and 2) that the contributions of direct sound and reverberant sound *in the recording space* are much better differentiated. In addition to the pleasures of these two direct benefits, they contribute to two important secondary effects: 1) vastly improved perceived soundfield depth and 2) improved solidity and localization of individual instruments/sections/voices in the image. I presume these secondary effects are the result of the improved timing cues the ear-brain system gets when these tiny variations in the signal are preserved rather than blurred together....
I'm hearing much more, even in older not-so-great digital transfers, than I've ever heard on them before (I'm not talking here about etched treble "detail"). For instance, in a jazz drummer's use of the brushes on a snare drum with snares off, we audiophiles are usually preoccupied with the sonic texture of the metal strands on the animal membrane and how accurately we can "feel" that--what I can now perceive, besides the dramatic decrease in the "hashiness" of that texture, is the slight contribution to the timbre made by the hollowness under the drumhead, even with very light strokes of the brush. My old 1980s CD transfer of the beautiful 1962 Szell/Pierre Fournier/Berlin Phil recording of the Dvorak cello concerto practically made me weep to hear some layering of depth among the orchestral sections, and good hall sound, and that wondrous singing tone of Fournier's. Even though it was a DG, it sounded more like a Decca of that period. It makes me wonder how great a good modern transfer could sound, even with the high-frequency limitations / anomalies of that era's microphones.
That says it quite well!

Which models can accept the plug-in phono module?

The VK-33, VK-33SE, and VK-42SE can all accept the optional plug-in phono module.

Can I add remote control capability or phono capability after I purchase my preamplifier?


Does my unit need to go back to the factory for the remote or phono upgrade?

The remote upgrade can be installed in the field. The phono-module installation requires a return to the factory.

Can I upgrade my VK-33 to a VK-33SE at a later date?

Yes. You will pay a nominal premium to have the upgrade done afterward as the unit will require more work than building it as a VK-33SE from the start.

What is involved in upgrading the VK-52SE to a VK-53SE?

The upgrade from the VK-52SE to the VK-53SE involves the following:

  1. Replacing the two SIX-PAK capacitor output modules with the new amorphous-core transformer assemblies.
  2. Adding/repacing components to optimize the gain structure for the new transformer-coupled circuitry.
  3. Adding the mu-metal shields to encapsulate the transformer modules.
  4. Adding new aluminum side panel supports.
  5. Replacing the rear panel with an all new rear panel (to accomodate the new top cover).
  6. Replacing the powder coated steel top cover with the new anodized aluminum top cover.
  7. Replacing the logo centerpiece as well as model plate

Is the user interface and programming capability the same in the VK-33 through REX II preamplifiers?


Do I need to be a computer programmer to use your preamplifiers?

No. They are easy to use right out of the box. No programming is required in order to start using the product effectively. Additionally, the programming feature is quite easy to use and many customers can use this feature without ever reading the manual.


Is the REX II Power amplifier a single-ended amplifier design?

No, the REX II Power amplifier is neither a traditional single-ended design nor a push-pull design. We refer to the REX II, VK-255SE and VK-655SE amplifiers as single-ended bridge designs. This fundamental circuit dates back to the early 1950's and was invented by Henry Wiggins while working for the ElectroVoice Company. The original name for this type of output topology was Circlotron. The single-ended bridge design relies upon two single-ended amplifiers arranged in a floating bridge formation. This differentiates it from other forms of bridge topologies, most of which effectively incorporate two push-pull sides. The output circuit is inherently balanced and is driven differentially from a preceding stage. The two DC bias currents that exist in each half of the output stage cancel each other in the load. It is a more expensive way of building an amplifier as it requires multiple floating power supplies, as opposed to the more traditional ground-referenced supplies. The benefits of this approach, however, include enhanced symmetry when compared to push-pull designs and lack of the DC saturation problem inherent to single-ended designs.

How do I upgrade my BAT stereo amplifier to a monoblock?

Except for the VK-220, all BAT stereo amplifiers, tube as well as solid-state, can be converted into a monoblock amplifier. These BAT amplifiers are converted to a monoblock by paralleling their inputs and outputs. In certain cases, the factory can provide a three-wire jumper that simply plugs in between the left and right channel boards to convert the inputs to monoblock operation. In other amplifiers, a set of zero ohm jumpers must be soldered to the main board. Four wires are then soldered across the speaker binding posts internally to parallel the outputs. In many cases, the amplifier need not come back to the factory for this upgrade. In all cases, however, some soldering is required. Please contact the factory to discuss the options available for your specific amplifier model.

Is there a big difference in sound between the monoblock amplifier and their stereo equivalent?

Yes! We have tried to be conservative with our customers in setting their expectations for this upgrade. Our customers, however, consistently tell us that the improvements are quite dramatic. In general, the sound from the monoblock amplifiers offers greater authority, a deeper soundstage, and more visceral bass reproduction than that from the stereo amplifier. You can even parallel our monoblocks together for even greater output capability.  There are a number of installations where our customers are using four BAT monoblocks in their system. With BAT tube amps, they are paralleled to create a super-triode amplifier. How does this work?  Just as a BAT stereo amplifier can be paralleled internally to create a BAT monoblock, two or even more BAT monoblocks can also be paralleled externally to create, in the case of our tube amps, a "super-triode amplifier"!  It is relatively straightforward to cable such a system and, yes, it provides a significant upgrade in sonic performance. We have a number of customers running this configuration throughout the world. As one of our distributors in Europe likes to say, "The sound is crazy good!"

I'm trying to decide between a VK-255SE and a VK-655SE power amplifier. Do you have any advice in this regard?

The VK-255SE and VK-655SE amplifiers sound very similar to each other as they are both based on the same two-stage, zero-feedback, single-ended bridge design. The two circuits are nearly identical, with the VK-255SE being sized for less power and single power transformer operation. As a result, the VK-655SE will, of course, play louder and is more authoritative in its bass reproduction. In many instances, the sonic differences between the two amplifiers stem from overall system synergy. Usually listeners will prefer the amplifier that is more properly "sized" to the job at hand. In other words, in a system with sensitive speakers, it would not be uncommon to prefer the VK-255SE over its bigger brother, simply because it will operate in its more comfortable range. On the other hand, when using more demanding speakers, the VK-655SE will outperform a VK-255SE that would then be running with more stress. Generally speaking, the VK-655SE is a more universal amplifier for the customer who frequently changes speakers. If a customer needs a higher output amplifier in anticipation of future speaker changes, the VK-655SE would be the better consideration.

I have an older preamplifier with RCA only outputs. Can I still use this preamplifier with your balanced power amplifiers?

Yes, simply order a pair of input adapters with your amplifier and it will be perfectly compatible with your single-ended preamplifier.