BAT Balanced Audio Technology REX preamp Mint customer trade-in

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Mint customer trade in 

BAT REX preamp silver/black with remote    
Excellent condition, original packaging and accessories.

Balanced Audio Technology's dual-chassis Rex preamplifier 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.