Musical Fidelity's Pure Class A monster amp

Musical Fidelity AMS50

Named after the company's founder and owner, the Antony Michaelson Signature model is a dual mono design, and claims less than 0.005% distortion across the audible frequency band, and only 0.008% right out at 50kHz.

In fact, the company says that "The AMS50 noise ratio is outstanding. Even on a 97dB sensitivity loudspeaker, it is inaudible unless you have your ear pressed to the tweeter. As far as we know, this is not a normal listening position!".

Inside, the amplifier is true dual mono, with the channels kept entirely apart, and is said to have excellent load-driving capability and an outstanding stability margin.

It has twin sets of speaker outputs, and both conventional RCA phono inputs and XLR connections for use with balanced preamps such as the company's recently-launched Primo. There's also a 12V trigger socket for remote switching

Available in black or silver, the casework features a three-piece front panel machined from solid miltary-specification aluminium. The top and back panels also machined from solid, and the badge made from medical-grade stainless steel.

But why is this 50W per channel amp so big? Simple, says Musical Fidelity: it's actually "the absolute minimum size possible for a pure Class A power amp.

"Its standing current is pure Class A, 50 Watts, 8 Ohms. This generates a fixed amount of heat. To keep the temperature rise of the heatsinks below 40 centigrade, a huge surface area is required for heat dissipation. The AMS50 has a surface area of six square metres. This results in a temperature rise of about 35 centigrade."