Product Review - Balanced Audio VK-5i Fully
Balanced Tube Preamplifier - December, 1997
J.E. Johnson, Jr.
Fully Balanced Tube Preamplifier
Manufacturer's FR Specs: 2 Hz - 300 kHz -3 dB
All Inputs and Outputs XLR (Balanced)
Size: 5 3/4" H x 19" W x 15 1/2" D
Weight: 31 pounds
Price: $4,500 USA (With Remote Control)
|Balanced Audio Technology, Inc., 26 Beethoven Drive, Wilmington, Delaware 19807 USA; Phone 302-999-8855; Fax 302-999-8818; Web http://www.balanced.com; E-Mail email@example.com|
Balanced Audio Technology (BAT) has been producing preamplifiers and power amplifiers since 1995. Only three years ago, and that's not very long to have been in business. I have been testing the BAT VK-5i, which is the latest version of their VK-5, the fully balanced tube preamplifier they announced as their first model at the 1995 Winter CES in Las Vegas. I've had the VK-5i for months, because I wanted to see if my first impressions would hold up. They have. This is one of the most exquisite products I have ever had the pleasure to test, and now, to own. It has become one of our reference components.
There are not any RCA jacks on the back. No unbalanced inputs or outputs. Not simply because this is a fully balanced component from input to output, but because the designers at BAT feel that balanced is the wave of the future, and that the best CD players and power amplifiers also have balanced topology. There are five sets of input jacks and three sets of output jacks, all XLR. If you want to connect single-ended components (RCA plugs on the cables), BAT supplies (optional) RCA-XLR adapters at $50/pair.
This entire package, including the preamplifier itself, the remote control, and the RCA-XLR adapters, have awesome construction quality. The front panel is solid, thick, brushed aluminum, with lathed control knobs. All of the front panel controls, including the on/off toggle, mute toggle, and LED readout, are easy to see in dim light. Inside the chassis is a heavy PC board with 3 ounce copper traces (meaning that there would be 3 ounces of copper per square foot of PC board if it were non-etched). The PC board layout is symmetrical. Ten tubes are neatly placed at nodes (regions of low vibration): Each channel has four 6922s and one 5881. There is only one gain stage, utilizing 6922 tubes as the basis for the circuit. Since the preamplifier is balanced, the signal for each channel is represented by two equal, but opposite-polarity waveforms. Nowhere along the signal-path do any of the waveforms touch ground (one of the defining characteristics of fully balanced topology). The remaining tubes in the preamplifier (both 6922s as well as 5881s) provide power supply management functions. These include a constant current source for the balanced circuit provided by the larger 5881 tube as well as AC shunt voltage regulation provided by the remaining 6922s.
The power supplies are enormous, having a total of 190 Joules of energy storage (95 Joules per channel - dual mono topology; four power capacitors and one toroidal transformer per channel). This is more like a power amplifier supply than a typical preamplifier supply. But if you think about it, the reasoning is logical. Whether preamplifier or power amplifier, the power supply will have difficulty if the impedance of what the component has to drive (power amplifier or speakers, respectively) is low. In such cases, the voltage drop across the load can cause waveform distortion (clipping), if the power supply is not adequate. The VK-5i is designed so it can deliver a perfect sinewave into an input impedance as low as 100 Ohms, although the specification states a minimum power amplifier input impedance of 10 kOhms! What this means is that the VK-5i will drive virtually any power amplifier to full ouput without incurring distortion problems. Of course, hugh power supplies come with a hefty price tag, but this is an "all out, no holds barred" product, not for the faint of heart. The input impedance of the VK-5i is 100 kOhms (each phase), also a nice figure that will be comfortable for any source. Because the power supply is so big, only a tiny amount of negative feedback is employed in the output circuit to maintain voltage on the load. No global feedback is used. The output impedance of the VK-5i is about 1 kOhm.
There are no tape loops, polarity inversion switches, or other contacts in the signal path that would be considered nice features, but what BAT considers signal-deteriorating items. From input to output for each channel's signal path, there are only the input XLR jack, source selector, single series resistor of the volume control, the single gain stage, an output capacitor, and the output XLR jack. That's it! Gain is 18 dB, distortion is rated at 0.01% at 2 V rms output, maximum output is 50 V rms, and polarity is non-inverting. All this from just one tube in the signal path.
Speaking of volume controls, the VK-5i uses one that is worth discussing. They call it a an electronic shunt volume control. Basically, what this does is put only one resistor at a time (Vishay Bulk Metal Foil Resistors) in series with the signal, instead of an increasing or decreasing number of resistors in series as the user adjusts the volume control. There are other types of volume controls, including digital, and conventional potentiometers. Each manufacturer uses what they feel are the best for their products, and BAT has chosen the shunt. There are 100 steps from 0 to 99, in 0.5 dB increments, with only 1 resistor in the signal path at each increment. Again, it's a very expensive way to do things, but . . . .
The remote control is made from a single piece of brushed aluminum, hollowed out to contain the electronics. It is one of the most beautiful I have ever seen. It is also very simple. Volume, mute, fade, 5 memory buttons, and unity gain. I set the review unit to a volume of 20, 30, 40, 50, and 60 (LED readout on the front panel). This allowed me to adjust the volume quickly in 5 dB steps. Very handy, very easy, and very elegant.
I connected the VK-5i to our McCormack CD Transport and DAC, LLano SA-3 Monoblock Power Amplifiers, Carver Platinum Speakers, Osborn Eclipse Speakers, and Nordost SPM Reference Balanced Interconnects and Speaker Cables.
The sound of the VK-5i is very easy to describe. Absolutely, totally listeneable and non-fatiguing for hours on end. It has an automatic warmup period of about a minute, during which the filaments are heated (soft start), and then the plate voltages are applied. I could notice a one-hour period after that when the sound quality slowly came up to full value. There are arguments on both sides of the fence as to whether tubes or solid state has the "best" sound, or the most "accurate" sound. I don't get involved in such arguments, because all I care about is the enjoyment factor. The technology approach I described above, represents BAT's engineering decisions. Engineers from other manufacturers have their own opinions about what is the best approach. I am not an electrical engineer, so, again, all I care about is how it sounds. After all the hype, white papers, and marketing glitz, does it sound good or not? The VK-5i, in my opinion, sounds terrific and is completely enjoyable. Violins and brass instruments retained their sheen, without being harsh in the slightest. Bass drums had depth. Detail was all there. The balanced design kept noise and hum all but absent, even with 25-foot interconnects.
One of the referees that I employ for single-blind tests came over to listen to the VK-5i. He is not a high-performance equipment aficionado, and is often shocked when I tell him the price of some of our review products. However, after hearing the VK-5i, he said it was worth the price. His ears are very good, and he can pick out even the slightest amount of edginess. His conclusion was that the VK-5i had no edginess at all, was wonderfully musical, and instead of excusing himself from the room after I got his opinions, stayed the entire evening to continue listening with me.
In summary, the Balanced Audio VK-5i sets new standards of construction and sound in the high-performance ("high-end") audio market. It's not surround sound, not THX, not DD, not DTS. None of those things. It is just plain fantastic.
John E. Johnson, Jr.
© Copyright 1997 Secrets of Home Theater & High Fidelity
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