Balanced Audio Technology Rex line preamplifier

[Κώστας Φ.]

• Description: Two-chassis, fully balanced, tubed, remote-controlled preamplifier with switchable absolute polarity.
• Tube complement: eight 6H30 in control module, two 5AR4, four 6C19, two 6H30, two 6C45 in power module.
• Inputs: 5 XLR. Outputs: 2 XLR (main), 1 XLR (tape).
• Volume-control resolution: 140 steps, 0.5dB each.
• Frequency range: 2Hz –200kHz.
• Maximum gain: 17dB.
• Maximum output: 50V.
• Distortion at 2V output: 0.005%.
• Noise: –100dB unweighted.
• Input impedance: 100k ohms minimum.
• Output impedance: 200 ohms.
• Power consumption: control module, 220VA; power module, 250VA.

"BAT's Rex

Balanced Audio Technology's dual-chassis Rex preamplifier ($18,500) features hefty control and power modules weighing 40 and 36 lbs, respectively, connected via two Neutrik-terminated umbilicals. Each receives power independently via separate AC cords because each contains a complete power supply for one polarity: negative in the power module, positive in the control module. This arrangement allows for close coupling of the power supply to the gain stage, while isolating the potentially noise-inducing parts of the circuit to the power module.

The modules have symmetrical, mirror-imaged layouts. The power module, with five tubes and separate toroidal transformers for each channel, includes 5AR4 tube rectification and a choice of three current-source tubes.

Two 6C19 tubes per channel is standard for the Rex's signal amplification. Add the X-PAK accessory, which consists of an alternate pair of user-switchable current-source boards, and you can use 6H30 SuperTubes instead —or remove the standard board altogether and try 5881s. My review sample came with the standard 6C19 configuration, which BAT feels provides the best combination of sound and electrical performance. In addition, the power supply incorporates a choice of user-switchable AC shunt voltage-regulator tubes (6C45 or 6H30), used to clean the power-supply rails and reduce minute fluctuations in DC voltage. The final DC filtration stage uses BAT's newest custom oil capacitors. Inside the control module reside four 6H30 differential gain-stage tubes per channel. The grand total is 18 tubes, though for all intents and purposes it's 16: only the selected pair of AC shunt voltage-regulation tubes is active.

BAT's Unistage circuit features a single gain element with no buffers or followers and zero global negative feedback. The 16-bit, digital shunt-control –based volume control uses Vishay Bulk Metal resistors to provide 140 steps of 0.5dB each. The tubes are coupled to the output jacks with oil-filled capacitors. John Atkinson's measurements of earlier BAT products, including the similarly circuited VK-51SE preamplifier (November 2003, Vol.26 No.11), have shown that even though they are physically large, these oil-have limited capacitance that raises the Rex's LF output impedance well above the specified output impedance of 200 ohms. While that can roll off the low-frequency response into low-impedance loads, the problem is more theoretical than practical. The Rex should be compatible with most modern power amplifiers having an input impedance of 50k ohms or higher.

...

Conclusion

If you're going to ask $18,500 for a preamplifier, you'd better deliver high technology and build quality, attractive cosmetics, ergonomic satisfaction, and —most difficult for a component that, by definition, should not express a sonic personality —sound that is simultaneously neutral and special.

The Balanced Audio Technology Rex manages both the high build quality and high tech, pleasing if somewhat dark appearance (better faceplate lighting would help), and excellent, full-featured ergonomics. Listened to at its 6C45 setting, was the Rex utterly neutral, adding nothing to the signal? No —no audio component can do that. However, what the all-tube Rex did to the signal was subtle, slightly additive without being overbearing, and, in the end, wholesome —similar to what a brilliant mastering job can do for an already excellent recording.

The Rex —or any excellent audio component —couldn't polish turds, but it did manage to put a brilliant shine on those recordings I consider to be the diamonds of my collection, while leaving intact the sharp edge of each gleaming facet. If you're lucky enough to spend some time with the BAT Rex, I think you'll agree that it's among the most beguiling-sounding control preamplifiers yet devised. Is it worth $18,500? Let your bank account be your guide; your ears will say Yes." -- Michael Fremer


"Although the failure of the left channel was disappointing and may have resulted from the less-than-white-gloves handling that UPS gives expensive audio gear, the Balanced Audio Technology Rex is a well-engineered piece of gear. However, there was no clue in its measured performance as to why Mikey preferred its sound with the 6C45 current-source tubes. For now, that will have to remain a mystery." -- John Atkinson


Full Review: Stereophile.com