PRESS18

TESTS

By Roy Gregory

The Kora CSA-1200 Hybrid, Class A Mono-bloc Amplifiers

INTRODUCTION :

The hi-fi world is one littered with obfuscation, contradiction and confusion, a market littered with too many products that flatter to deceive, fail to deliver or simply aren’t quite what they seem. Just try keeping count of the ‘Class A’ amplifiers – that aren’t: the hybrid amplifiers that claim to offer the best of both worlds – but don’t; the ‘revolutionary’ breakthroughs or innovations that will transform performance – which we’ve seen before (at least if you go back far enough); the French products that are decidedly different, distinctly interesting – but ultimately fail. They’re common enough boxes and, at first glance, the Kora CSA-1200 (1channel, 200Watts) mono-bloc amplifier might easily tick them all. But in this case, and at all but €60,000 for a pair of these impressively powerful and beautifully finished amps, it’s well worth a second glance at a story that’s more interesting and convoluted that it first appears.

Kora (the company) has been around for several decades, but changed hands in 2017, when it was acquired by Bruno Vander Elst, a long-time and highly regarded consultant to the wider French audio industry. He used the established brand as a launch pad for a new range of products based on an entirely new tube amplification topology, an inherently stable, balanced arrangement of two twin-triodes per channel that ran the tubes from a precise current source and at around 20% of their current capability (around 2.5-3.0mA, rather than the more usual 10mA) to produce a balanced output. The tubes were operated so far within their comfort zone that Kora claimed that tube quality and even tube type are virtually irrelevant, performance and linearity being defined by the circuit rather than the devices. Functionally, it’s a topology that mimics an op-amp, a self-contained amplification stage that can be dropped into a wider circuit context to fulfil various functions. This “Square Tube” circuit (four twin-triodes creating a single, stereo amplification stage) found its way into a range of powerful but surprisingly affordable, hybrid integrated amplifiers, followed by a DAC, CD player, line-stage and beefy Class AB power amp, acting as a driver or output stage. More recently, the company has launched a range of up-market, hybrid topology, Class A designs, of which the CSA-1200 is the flagship model.