Supercharger. It's a word that has an undoubtedly romantic ring, reminiscent of the Hon. Henry Birkin and his Bentley Boys, sweeping their way to four successive Le Mans victories in the 1920s.

However, the automotive engineering reality is actually a little more prosaic, with the 'charge' simply being the explosive air/fuel mixture that's fed into the engine, and the 'super' referring to the process whereby the air is pressurised with a fan to get more 'charge' into the engine, thus increasing its power.

The analogy with hi-fi may seem a little obscure, though it's not hard to understand why Musical Fidelity's marketing department has come up with the 'Supercharger' tag, for a component that does, at least to some extent, offer a new concept in power amplification.

Of course, to the less romantically inclined, the 550K is simply a high-power monoblock power amplifier. To Musical Fidelity's patron, Antony Michaelson, however, it can also be seen as an excellent opportunity to 'supercharge' your existing system, enabling it to deliver truly realistic musical dynamics.

To achieve this chameleon role, each monoblock unit is equipped with a 'normal' line-level RCA phono socket input, alongside a high-level input that's accessed via a pair of speaker terminals. The 550K can therefore be used as a regular power amplifier, fed from a preamplifier, passive system controller, or a variable output CD player.

However, for its intended Supercharger role, the 550K needs to be located close to the loudspeakers. The speaker cables are then disconnected from the speaker and reconnected to the 550K, while the extra speaker cables that are supplied with the amp are connected to the speakers. Find somewhere to plug in the IEC mains lead and, hey presto, the system now has more than 550 watts of power.

Inserting the complexity of an extra power amplifier into the hi-fi chain might not sound a particularly good idea from a transparency angle, but a compensating advantage is that the less-powerful system amplifier is freed from the relatively difficult task of driving a complex loudspeaker load. Driving the 550K's resistive (approximately 55ohm) input should make its life significantly easier.