Musical Fidelity A200 amplifier
There is nothing complicated about Class A amplifiers. The basic difference between them and the more common Class B (and AB) designs is in the biasing applied to the amplifier’s gain stage transistors.
In order that both halves (positive- and negative-going) of the audio signal can be amplified equally and with minimal distortion, the transistors in a Class A amplifier are biased to operate at the mid-point of the linear portion of their transfer characteristic. This is in contrast to Class B amplifiers where the transistors are biased to the bottom of their characteristic, where non
linearities occur. In true Class B this is zero bias. Each of a pair of transistors thus biased handles only one half of each cycle of the input audio signal. Where one transistor hands over to the other the phenomenon known as crossover distortion occurs. The problem worsens as the signal amplitude decreases. Class A operation does away with this distortion, and one advantage is improved resolution of low level signals.
The price to be paid for this audible improvement is the Class A amplifier’s lack of efficiency. In an output stage this can be as low as 20 per cent. Hence for reasonable output capability considerable energy is converted to heat – large amounts thereof even in low wattage amplifiers! If this heat is not dispersed effectively the transistors will enter a cycle of heating up and passing more current until they self destruct. In the same way that dogs tend to bear a resemblance to their owners, I think that amplifiers take on the personality of their manufacturers! That’s certainly true of Musical Fidelity products: once you’ve met the dapper and ebullient Anthony Michaelson you know that he could never produce a mundane black box. Anything he makes, even a simple integrated, is going to have a distinctive, individual character.
The £699, A200 is the company’s state-of-the-art one-box amplifier. Clothed in the same garb as the smaller A class integrateds it looks strikingly different alongside more conventional offerings. However, its styling is not purely an aesthetic consideration: there’s method behind its modernness. As the panel copy (above) explains, Class A amplifiers run hot, especially when they are idling or only passing small signal voltages. Hence they require massive heatsinking or ventilation to prevent their transistors
going into thermal runaway. The whole corrugated top plate of the A200 is intended to act as a heatsink, though in practice the whole case joins in to help dissipate those unwanted watts. In an average room the casework reaches roughly 55oC under idle conditions. In a small, centrally-heated, poorly ventilated room listeners sitting close to the A200 must consider the possible danger of heat exhaustion! The answer is to wear safari clothing and keep a crate of Perrier beside your chair.
The A200 offers little in the way of facilities: all it allows the user to do is switch it on, select which source is to be listened to, and adjust the gain. There’s a small push button on the rear panel to choose between the two phono options (moving coil or magnet). Not an amplifier for the knob-twiddler! Six inputs are provided (access via gold-plated phono sockets) for disc, CD, tuner, CDV, and two tape decks. Loudspeaker cable hook-up is courtesy of sturdy binding posts.
I listened to the A200 with vinyl replay from two decks: a Linn LP12 Lingo, Naim ARO, Linn Troika moving coil; and a Pink Triangle Anniversary with SME V and Shure Ultra 500 moving magnet. CD came from a Micromega Trio. Partnering loudspeakers included Naim SBL in passive configuration, Cyrus 780, and Musical Fidelity’s own MC5.Cable was Naim NAC A5.
From the outset it was apparent that one’s opinion of this amplifier would be cemented by the main source in use. Whilst the phono stages were acceptable the A200 really shines through its line level stages. Musical Fidelity, as a company, has `gone over’ to Compact Disc and clearly this amplifier was developed with this as the predominant medium.
Using music as varied as female folk singers, symphony orchestras and small jazz combos, the A200 sounded open, spacious and clean, despite a hint of valve-like euphony. Vocalist Mary Black, on her CD No Frontiers, was presented with an intimate clarity and a wealth of detail that displayed her singing technique with ease and commendable expression. Her vibrato, intonation, phrasing, and breathing, the depth of texture within her voice, were etched with precision and human warmth. Her accord with
her backing musicians was similarly portrayed, the ensemble playing as an integrated and rhythmically coordinated whole.
Panufnik’s Violin Concerto exuded musical and emotional passion, and committed playing from London Musici. The A200 paid due respect to this atmospheric recording – a particularly fine effort by Technics. Again the music flowed with a natural, unforced ease, and the amplifier successfully conveyed the weight of the orchestra: in respect of its showing here its 60 Watt rating would be judged as conservative – it gave the impression of more substantial reserves of power.
In the search for further evidence of this facet of the amplifier’s performance I turned to ’79 Revisited – The New Wave of British Heavy Metal and played a couple of tracks by Def Leppard and Weapon (I can visualise the expression of disgust gracing Mr Michaelson’s face as he reads this!). The A200 didn’t, as I expected it might, try to polish off this music’s rough edges. All the energy, excitement and grunge came through untainted by unwarranted politeness or refinement.
The amplifier has an undoubted character, and this is more noticeable through the phono stages: the moving magnet proving more open and uncolored in this instance than the moving coil. Christine Collister’s voice, on her new LP with partner Clive Gregson Love Is A Strange Hotel, sounded rather more husky and hoarse than in real life or through my regular Naim amps. This added colour is, however, never unpleasant and is, in the main, euphonic. It tends to add a warmth, a tonal bloom to instruments, which can make recordings sound that little bit more human and less mechanical. But instruments like acoustic bass, when recorded at high levels, can do without this. Note shape becomes a little ill-defined, and timbre more cloudy than
So try before you buy if you regularly use a record player. CD users can be more certain: if searching for an amplifier with an added touch of warmth that doesn’t get in the way of the music, the A200 deserves to be heard. Even by those whose tastes combine Def Leppard and Panufnik!