These are a rare and unusual concept in the hi-fi world.

Q.If you're interested in musical realism in a home environment, how much power do you actually need?

A.More than you may expect, according to Musical Fidelity's founder Antony Michaelson, who says that with loudspeakers of domestic sensitivity, you need at least 500W to faithfully reproduce music's transient peaks at a realistic level.

This is just NOT available with your favourite low-powered amplifier.

A 100Wpc amplifier with 87dB-sensitive speakers will reproduce a maximum spl of just 100dB, which doesn't reach live levels, which can be louder than 105 plus db!

The answer is the Musical Fidelity 550K Supercharger which has the same 550W circuit as Musical Fidelity's kW550 integrated amp, which is quiet, linear, tonally superb producing the desired high powers—550W into 8 ohms or 750W into 4 ohms—with ultra-low levels of distortion, swinging 250 amps of current peak to peak, with a massive voltage swing.

In the supercharger, this same circuit is used in a switchable low-gain configuration so you can run them as stand alone power amps, or connect your existing amplifier's output from its speaker terminals to the 550K's 4mm banana type input terminals, that Includes flea powered and vintage valve amps, which feed the Supercharger with your existing speaker cables, placing them near to the speakers, running a short jumper from their output to the speaker inputs, thus preserving the characteristics of the original device.

The Superchargers drive the speakers and the source amp sees a benign, stable, easy to drive constant impedance load.

When testing I found it difficult to describe its sound, as oddly it didn’t really have one,it was just clean and....Neutral.

They were unfazed by difficult loads such as Quad Esl’s which I tried,with no problems.

MF says that an amplifier driving the 550K draws only about 7% of the current required to drive a typical loudspeaker so 93% of the heavy lifting is done by the Superchargers.

Which means your favourite power amplifier can now act as a preamplifier for the 550K and retain its sonic signature in your system....But aurally expanded.

You can also flip a switch, to run a line level source, such as a CD player or a (valve?) pre-amp through the RCA phono inputs, if that is your preference.

So it is really 3 amps in one, you can use it as a pair of stand alone power amps with a line level source, with a pre-amp, or power amplifier, at the front end, as the name suggests to Supercharge your existing set up, whatever suits your ears or needs.

If you like the sound of your amplifier and it's a valve (tube) amp with a high output impedance that interacts with a loudspeaker's oscillating impedance producing frequency-response distortions, driving a pair of 550K’s instead takes care of that too!

The mono-blocks are each a cylindrical heat sink, with the output devices bolted to the inside vertically.

They are electric bill friendly with a signal-sensing relay to turn on when music plays.

The condition overall is excellent, apart from a couple of dings on the top rims of the lids and on the fins shown in the photos where when they were delivered to me originally from Germany they were not packed well enough and banged together in transit.

Despite which,being so rare,I kept them anyway as the minor cosmetic imperfections were not really noticeable in use.

They have sat idle for a while now as I have changed all my system (yet again) so they need a new home for somebody who will appreciate what they bring to the party as a unique product.

Both amps were tested before packing, using the same Fostex professionalCD copier/player, RME Adi 2 pro DAC, SPL Phonitor 2 as preamp, and a Naim 250 clone power amp, to the speaker inputs of each Supercharger, with Dynaudio speakers, and again but with the SPL as line level source on the RCA inputs, both worked perfectly as expected.
I was asked a question about what they did in practice, and used a car engine as parison;
'its about taking what power reserves you have in the electrics of your amplification
system and giving it a breathing space, so it isn't running flat out when you get a
musical peak. it has nothing to do with room or speaker size.
Depending on the recording and program material some transient peaks can be more
than the set up is capable of responding too 'accurately' as it is at its limit, and gives a
subjective whimper rather than a bang
then the supercharger kicks in and takes over as it has far more headroom in its rating.
think of a normally rated car poodling along at 50mph needing to pass another vehicle,
then the gap narrows as there is suddenly an ing lorry, you put your foot down
and there is not enough instant power to safely close the gap, and you narrowly miss the
ing at you, the same thing happens
but you have a turbo on your engine (supercharger) as you accelerate to avoid the lorry,
it kicks in and sucks more fuel in mixes presses the hot un-burnt exhaust gas,
back into the engine, giving you a kick in the pants burst of power so that you easily
close the gap with loads of space to spare, as the lorry is still way off and nowhere near
you.

That's the principle
it takes an under-powered amplifier and allows it to act as a pre-amp
giving it a light electrical load and plenty of room to breathe, so the 'heavy lifting
(electrically) of making the speakers move is done by the supercharger, so when you hit
a peak you have bags of headroom that does not run out of steam, and
plays back what is on the recording
rather than effectively muting (compressing) it.
So a punch sounds like a punch rather than a fart! (parison but that's the
idea)

These are Big mono amps same circuit as the 550k silly money integrated amps with
the big transformer box, that get all the rave reviews for 6 times the asking price of
these'.

These amps are a high quality product built to a very high standard.

They will be very well packed for shipping as shown in the last photos, bubble wrapped first, strapped with with a polystyrene slab jacket, inside an outer tough waterproof corex plastic shell, as I personally prefer to prevent any potential damage in transit!