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'So is it really loud now?' - that's the reaction I keep getting when I mention I'm running a pair of Musical Fidelity Supercharger 550k power amps in my system, writes Andrew Everard. And one of my fellow Gramophone writers wants to try them, but is worried he'll have to wait until the neighbours are out.

That's not the point about the Superchargers - yes, they will make your system go louder if you really want, but at £3000 a pair they might seem quite an expensive way of achieving that. No, what the cylindrical MF amps are all about is improving the dynamics of your system, from the big stuff right down to the way fine detail is conveyed.[/intro]

Never let it be said that Musical Fidelity's Antony Michaelson isn't a persuasive salesman. When he gets behind a product - and he's very much behind the Superchargers - you tend to know all about it. So far we've had a visit to the listening rooms here in Teddington followed up with a delivery of a stack of samples, and since taking a pair of Superchargers home I've received a number of calls, the main essence of which has been 'So...?'.

Actually, I didn't need that much convincing - I'm yet to see what the WHFSV review team make of the units they have, but my initial reaction when I heard a demonstration was what I've referred to in the past as 'one of those silly grin moments'. So I was pretty keen to get a pair home and give them a try. Well, a couple of weeks on, and I've used them with a number of amps, including an old Marantz MusicLine combination, Shanling's flea-powered but oh-so-sweet-sounding MC-30 'music centre' and, most of the time, the Onkyo TX-SR875 receiver.

Now what I heard someone refer to the other week as 'the big Onk' is no slouch when it comes to music-making in stereo - and you're hearing that from someone who used to believe AV receivers were akin to the great evil when it came to music systems - but the Superchargers take it into a whole new league.

As I write this I'm listening to some Bach solo string music arranged for the lute and played by Nigel North in a four-disc Linn box-set available for a giveaway £20. The system is Naim DVD5, the Onkyo, PMC OB1s with Tannoy ST50 SuperTweeters, with all the cabling from Chord, and I have to say I have never heard better-sounding music in this room in the five years since we moved here.

Solo lute music may not be the kind of material for which most people would consider massive amp power an essential, but with the chargers in harness the music takes on a fluidity, presence and impact way beyond the already impressive results achievable when the speakers are connected directly to the receiver.

Pull them out and the music is pleasant, enjoyable but a little flat, though still remarkable by AV receiver standards; plug them back in and the whole sound opens up while at the same time snapping into sharp focus. In fact, the effect is even more pronounced when taking the MFs out than it is when plugging them in.

When I set the system up I re-ran the Onkyo's automatic calibration system, and noted the front left and right channels were now set with a few decibels of extra roll-off, which would surely defeat the whole purpose of having the chargers in the system. Far from it: listening to one of the Proms the other night on BBC HD I was struck by the gorgeous timbres being revealed in the period instruments of the joint forces of the Orchestra of the Age of Enlightenment and the Freiburg Baroque Orchestra.

Having recorded the concert, I then tried the Music for the Royal Fireworks both with and without the Superchargers, the difference best summed up as 'very nice' on one hand, and 'wow!' on the other. So why do they work? Well, if you wish you can take with a pinch of salt the slide-rule Musical Fidelity has produced to show you how your system matches up to the demands of your speakers and real music, but the principle seems to be all about taking the pressure off your amplifier.

The theory goes that, driving the benign load the Superchargers present, your amplifier can reveal its true qualities, leaving the chargers to do all the really hard slog. It's a persuasive argument, but one I wasn't sure about - I had bad memories of using booster amps taking speaker-level input in car systems back in my dim and distant, and remembered just how bad they sounded. But using the MF amps dispels any such doubts.

In fact, now I've been living with the Superchargers for getting on for three weeks, I have to close with a note of caution: these are probably not amplifiers you want to audition if you have any weakness in the 'Oh go on, then - do you take credit cards?' department...

More after the break