No, the VK-60 is neither a traditional single-ended design nor a push-pull design. We refer to the VK-60 through VK-1000 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.

Have there been engineering changes to the VK-60 since its introduction?

Yes, there have been numerous small enhancements to the VK-60, predominately involving its protection circuits as well as its power supply functions. The newer VK-60's do sound somewhat better than the older units, but fortunately, the factory can upgrade an older VK-60 with these modifications for a nominal fee.

How do I upgrade my VK-60 stereo unit to a VK-60 monoblock?

The VK-60 stereo is converted to a VK-60 monoblock by paralleling its inputs and outputs. 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. Four wires are then soldered across the speaker binding posts internally to parallel the outputs. In most cases, the VK-60 need not come back to the factory for this upgrade. It can be done in the field by any qualified technician.

Is there a big difference in sound between the VK-60 monoblocks and a VK-60 stereo unit?

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 VK-60 monoblocks offers greater authority, a deeper soundstage, and more visceral bass reproduction than that from a VK-60 stereo. I've heard of a customer using four VK-60 monoblocks in his system. He mentioned that they were paralleled to create a super-triode amplifier. Can you explain? Just as a stereo VK-60 can be paralleled internally to create a VK-60 monoblock, two or even more VK-60 monoblocks can also be paralleled externally to create the "super-triode amplifier" that you mention. 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 now running this configuration throughout the world. As our distributor in Switzerland likes to say, "The sound is crazy good!"

I'm trying to decide between a VK-200 and a VK-500 power amplifier. Do you have any advice in this regard?

The VK-200 and VK-500 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-200 being sized for less power and single power transformer operation. As a result, the VK-500 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-200 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-500 will outperform a VK-200 that would then be running with more stress. Generally speaking, the VK-500 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-500 would be the better consideration.

What is the optional BAT-PAK for the VK-500? Why should I consider buying it?

The BAT-PAK is an internally installed set of power supply filter capacitors that triple the energy storage of the standard VK-500 from 350 joules to 1150 joules. Please note that although it does not change the steady state power output of the VK-500, the transient dynamic power capability of the amplifier will improve dramatically. The additional power supply energy storage obtained from the BAT-PAK provides the VK-500 with greater authority in the reproduction of low-bass and mid-bass transients. The improvement is most apparent on demanding full-range speaker systems.

I'm ready to upgrade my VK-500 stereo unit to a VK-1000 monoblock. What is involved in this procedure?

The VK-500 will have to come back to the factory to be upgraded to a VK-1000. The front-panel as well as the back-panel are changed to new VK-1000 panels, and the circuit modifications required to convert the unit to monoblock operation are performed. Contact the factory for more detailed pricing or to schedule your upgrade.

Is the sound of the VK-1000 a big step up over the sound of the VK-500?

Yes! The improvement is similar to moving from a VK-60 stereo to a VK-60 monoblock. The higher current delivery of the VK-1000 imparts a greater ease to the reproduction of music. The superiority of the VK-1000 becomes more apparent as the musical score becomes more complex or more demanding.

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.