Stereo Amplifier

Review: Musical Fidelity A1 Stereo Amplifier

Enthusiasts with audiophile aspirations but lacking the friendly bank manager needed to fund their hobby to the full are naturally attracted to small 'minimalist' amplifiers which omit such luxuries as meters, balance and even tone controls whilst offering high-quality reproduction on a budget. This country is well endowed with designers and manufacturers of such amplifiers-indeed some of the smaller companies make nothing else. Musical Fidelity Limited have built their reputation on quite large, and relatively expensive, audiophile power amplifiers, preamplifiers and an integrated amplifier.

This A1 integrated amplifier nominally rated at 20 Watts-per-channel is therefore very much the baby of the Musical Fidelity family. It is a fairly compact design in matt black relieved by light blue lettering. The few controls are mounted almost flush with the front panel but the latter slopes back at the bottom for easy thumbwheel operation. The only non-switch control is the rotary volume control which has no scale markings. The matching source selector switch has five positions, lining up with the five pairs of phono sockets on the rear panel for phono, CD, tuner, auxiliary and tape. A push-button switch on the rear panel changes over the phono circuitry for either moving-coil or moving-magnet cartridges. The only other controls are half-round push-switches for mains on/off (with red indicator lamp) and tape monitor.

A further pair of phono sockets on the rear panel supplies the recording output for a tape machine. There is no headphone socket (a pity) and the loudspeaker sockets are of a good quality type but designed to accept only 4mm plugs (no bare wires). The instruction leaflet is brief and to the point but does explain, for example, that it would be possible to dub from one tape machine to another by plugging the playback machine into the auxiliary input.

Class A

A principal claim for our attention comes from the fact that the A1 follows the philosophy of the more powerful Musical Fidelity amplifiers by operating in Class A. This mode of operation was traditional in the earliest thermionic valve (tube) amplifiers but is nowadays rarely encountered except in relatively expensive solid state (transistor) amplifiers and a few valve designs. Its main feature is that the output stages carry current continuously, whereas the more common Class B etc. implies switching between alternative opposite-polarity (push-pull) networks. Class B and its derivatives have the advantage of carrying very little current until an audio signal comes along, and so they can be very efficient in terms of power transfer and run at comparatively low temperatures.

Heat dissipation

Class A amplifiers draw a fair amount of current from the mains, whether they are carrying audio signals or not. They are therefore very inefficient and have to meet the problem of dissipating all that non-audio power as heat. The only possible reason for using Class A, therefore, is in an attempt to secure better overall sound quality than an equivalent Class B design where some degree of switching ("crossover") distortion is inevitable. In practice, a well-designed Class A amplifier does indeed produce high fidelity signals and, even when the input level exceeds the design maximum, the onset of distortion is much more innocuous than in other amplifier configurations.

The A1 designer has approached the problem of heat dissipation by constructing the whole top panel (in fact almost the whole case) as an effective heatsink and bolting it to a metal bar carrying the output transistors. Even so the amplifier runs rather too hot to touch (the makers say 50°C is normal) and so it is absolutely imperative that the Musical Fidelity A1 is located in a well ventilated position, with the top kept clean and clear of obstacles.

How it performed

The modest 20 Watts rating will already have suggested to most readers that the A1 is best used with reasonably sensitive loudspeakers (the leaflet suggests a minimum of 88dBA for 1 Watt). I would agree with this and go so far as to suggest that if you want to use very low efficiency speakers or listen at very high levels this amplifier would be a poor choice. That said, I found that normal listening levels were reached with a welcome sense of openness and musical ease: no harsh onset of distortion on peaks and a fine consistency of tone on voices and instruments alike. Background noise was amazingly inaudible, a good feature for use in conjunction with Compact Discs and LPs in good condition (as the majority of mine are). All inputs were handled well, even the moving-coil input where the source signal is at only a small fraction of a millvolt - though I did experience a small amount of electrical and radio interference on MC until I interpolated one of my suppressor adaptors.

As the Specification Table shows, the amplifier met its claims on all counts. Output power at 1kHz could be raised to 28 Watts before the gentlest of Class A-type clipping could be detected. The unit did run out of steam eventually at low and high frequencies, but subjectively this did not diminish my good impressions to any material extent. Compact Discs remained impressive dynamically, and were often less strident than with some other systems. This is a sweet sounding amplifier that can be recommended for any vinyl disc, CD, tape or radio listening situation where tone controls etc. are not needed and the decibel requirement is not over the top.