BAT REX 500 Power Amplifier

BAT REX 500 Power Amplifier

Less could be very far more in BAT’s flagship stereo energy amp the place its third-generation ‘SuperPak+’ PSU meets a completely balanced output stage that includes N-channel MOSFETs

Here’s a enjoyable sport to play: look by means of the product catalogue of US producer Balanced Audio Technology and attempt to spot the odd one out. It ought to solely take you a matter of seconds as a result of all of its present fashions, bar one, make use of tubes in both their energy or preamp levels. And in the event you nonetheless have not realised I’m speaking concerning the new REX 500 energy amplifier, it is the one which’s roughly twice as massive as all of the others.

A two-channel mannequin rated at 500W a aspect, however with the choice to be specified at buy as a 1kW mono design, the REX 500 is described as BAT’s ‘flagship stable state’ amplifier, however at £22,500 additionally counts as its flagship amp, full cease. Below it’s the £14,995 tube-toting VK-90t. This can be one thing of a beast, claiming 2x80W from its 6C33C-B triode energy tubes and weighing 45kg, but the REX 500 goes additional, tipping the scales at 63.5kg. The arc-shaped deal with mounted to its rear, which echoes a design element discovered on different BAT fashions, is subsequently helpful on the subject of getting the amplifier in place.

Secret Sauce

BAT’s net web page, and accompanying ‘white paper’, for the REX 500 inform us that the amplifier employs solely N-channel FETs in each its driver and energy levels, and offers a touch of the considering behind its ‘SuperPak’ energy provides with their parallel mixture of electrolytic and hybrid silver foil/oil reservoir capacitors. There isn’t any point out, nonetheless, of the excessive working temperature (55-65oC throughout the chassis) or the actual fact it is pulling 500W from the wall when idle.

Designer Victor Khomenko could be very cautious about calling the REX 500 a ‘Class A amplifier’ and prefers the time period ‘closely biased Class A/B’. Furthermore, whereas the amplifier doesn’t use complementary PNP/NPN transistor pairs, neither is its design quasi-complementary within the vogue of so many early transistor amps from the Nineteen Sixties. Instead, the REX 500 takes its design cues from the Circlotron triode tube circuit patented by Wiggins within the US in 1958, although others had revealed comparable topologies earlier. In truth, all BAT’s amplifiers, whether or not tube or transistor, have employed a modified type of the bridged Circlotron configuration.

Float Like A Butterfly…

The REX 500 follows go well with with two single-ended teams of 12 N-channel FETs per channel, bridged and with floating energy provides. Moreover, as a result of the previous N-channel driver stage is totally balanced, each phases are already current to feed the 2 bridged single-ended blocks straight (ie, no further inverter stage is required).

The circuit appears elegant sufficient, and advantages from a really delicate transition from Class A to A/B at larger energy, however requires nice care in its optimisation and stability – the identical might be stated when trying to measure this amplifier. Also, as a result of the REX 500’s output is floating it shouldn’t be related to any loudspeaker with a grounded ‘black’ terminal…

That consideration apart, setup and operation are a breeze – as soon as you have realised the amp has two IEC sockets to feed its twin, separate PSUs, one other side of its ‘true dual-mono design’. In between these are PSU fuse holders, and above are reset buttons for every channel must you handle to set off the REX 500’s safety circuits. Inputs are supplied on balanced XLR solely, to match the connections on BAT’s REX 3 preamplifier.

Heavy Metal

While the load of this amp would possibly pose some set up questions – it would absolutely find yourself on a low stand on the ground – it is just a bit greater than ‘commonplace width’ at 483mm vast and BAT’s industrial design does assist it seem a minimum of considerably glossy. The metallic chassis, supplied in silver or black, has a sensible brushed end and a slight swoop impact courtesy of the widened entrance fascia. BAT’s emblem and the standby/energy button take centre-stage: the one factor upsetting its symmetry is the mannequin quantity, engraved on the lefthand aspect. The general impression is of a premium amp that is been very effectively put collectively.

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March 7, 2024 at 11:35PM