Musical Fidelity A200 Amplifier
This is the third integrated amplifier using Class A operation that Musical Fidelity have released, following the 20 Watts per channel model A1 and the subsequent 50 Watts version, the A100. These models are complemented by the Class AB model B1 and of course by several separate pre and power amplifier models.
Class A operation has two principal drawbacks. First it is inefficient, because the circuit draws a continuous high level of current from its power supply, regardless of the signal level. Second, as a corollary of that, the current not required at the loud speakers at any given instant is dissipated as heat. For a given power output, Class A amplifiers therefore cost more to run and tend to get rather hot. Where they score both in theory and, many argue, in practice, is in undeniably faithful signal processing (accepting the proviso of sensible design). The problems of overcoming the crossover distortion which are inherent with Class B operation as the output devices pass the signal from one to another do not arise with Class A and even the most widely used output configuration, which employs a modestly biased form of output configuration termed Class AB, has potential limitations because of the demands it makes on its power supply and is anyway a less simple way of achieving the desired result.
Simple is certainly the word for the A200, although I mean no criticism in saying that - quite the reverse in fact. It s intent in this regard is apparent from a first glance in the clean, attractive lines of the unit and in its small complement of controls. This is a minimalist design allowing just a volume control and an input selector in addition to the mains On/Off button. There are no filters, tone or balance controls, no headphones socket, no provision for connecting additional loudspeakers.
The Volume control knob is continuously variable (as opposed to stepped) and has no graduation marks, just a light blue plastics pointer let into its high quality spun aluminium knob. An identical knob is fitted to the six-position rotary input selector which carries inputs labelled Phono (MM or MC, selected from a push-switch on the rear panel), CD, Tuner, CDV (sound signals), Tape 1 and Tape 2. The mains button is a half-moon type as on the A1 and A100, the top of the circle completed with a red lens through which the power-on LED shines.
The rear panel carries eight pairs of gold-plated phono sockets for the signal inputs and tape record outlets, the aforementioned MM/MC selector switch, a ground screw for the pickup arm earth lead, two pairs of 4mm socket/binding posts for the loudspeaker connections, a chassis-mounted fuse holder and the captive two-core mains lead, this terminated in a moulded two-pin, plug. I should mention the extremely impressive case-work which MF have developed for these new designs. The chassis is an L-section folded steel plate which forms the base and rear panel. To this is screwed elaborate anodized aluminium castings for the attractively bevelled front panel (a complex structure, this, with a second vertical panel behind the fascia), side plates and lid. The overall result has an impressively substantial feel to it and an appearance which exudes quality
The entire circuit is built on one single-sided glass-fibre printed circuit board which occupies around 70 per cent of the chassis floor area. On the left of this is a large toroid al mains transformer. The volume control potentiometer and input se lector switch are high quality Alps devices located sensibly at the heart of the circuitry near the rear panel and are driven from the front panel knobs by long steel rods. The eight output transistors (four per channel) are located centrally on the board itself, mounted through a large aluminium block which mate s with another above it to form an overall 'L'-section. This in turn connects with the heavily ribbed aluminium cabinet lid to form the necessarily massive overall heatsink required in a Class A amplifier of this power rating. The running temperature of this lid is substantial (your hand wouldn't remain on it for long) but at least MF have managed without a fan, which is always a good idea if possible, if only because they tend to be audible (this is a limitation of the A100, I feel). There is a thermal cutout mounted on the heats ink which will disconnect the mains supply if it trips and will only re-engage when temperature has reduced. At no time during several weeks of use did this happen.
The power supply is massive, with a single bridge rectifier and no less than three pairs of 10,000μF electrolytic capacitors forming a sequence of RC filters for the output, line-level and pick up cartridge stage s. A mixture of discrete and integrated circuit blocks (TL082/084 types) is employed both for the RIAA gain and equalization, and the line-level buffering. High quality components are used throughout and the standard of construction is also high.
How it performed
The specification provided with the A200 is somewhat rudimentary, as are its modest claims in respect of the lab performance. Typically the total harmonic distortion figures via the line-level input s were far below the one per cent level quoted and the signal-to-noise ratios similarly exceeded the published figures. My plot of the RIAA response showed that it followed the IEC recommendation closely, just 0.27dB down at 20kHz. All the line level inputs have the same sensitivity of 200mV which means that the volume control will invariably be set lower for CD than for the other inputs. The MM gain is 35dB and the MC 56dB or so, which will suit a wide range of cartridge outputs, but some MC types may prefer to 'see' a lower impedance. The tape outputs are un-buffered which means that the output impedance will depend upon the source impedance of the selected input device, although as we've said many times before, that shouldn't be a problem with most modern ancillary units.
Listening proceeded well using a mixture of LP and CD sources, and I was immediately impressed by the ease and solidity conveyed with a couple of favourite LP recordings-Benjamin Brillen's Spring Symphony and Debussy's Jeux and Nocturnes. The often complex textures of the former and the extremely delicate, filigree lines of the latter, all but merging with the acoustic itself, were conveyed most effectively, with a keen sense of the ambience.
Similarly impressive were the result s with CD, the coherence in ambience of good recordings well conveyed and again very solid. The hushed, 'nature's awakening' D major strings opening of Webern's Im Sommerwind is a good example of the challenge well met in the presentation of subtle nuances of texture and sound-stage. Stereo detail is always crisply defined and the A200 gives that important sense of its authority, that feeling of power in reserve, which confirms it s pedigree.
My one significant dislike about the A200 is a seemingly trivial point concerning the practical business of turning the rotary input selector t The knob is almost flush with the fascia, the intention being that it should be turned thumbwheel fashion by it s lower edge. But since the knob barrel is smooth, this is far less easy than it ought to be unless you happen to have 'sticky' fingers. I gather that an 'O'-ring may be filled around the knobs of late r models, which would certainly solve the problem. The only other point is the filled two-pin mains plug. This is of the type which could be used with an adaptor, but only if that ha s a fu se of its own - otherwise the A200's filled cable will be protected only by the 30 Amp fuse back at the mains distribution box, which is unsafe. The plug should be replaced with a proper, fused three -pin plug.
Musical Fidelity have once again come up with an impressive product. The A200 is most attractive to my mind-refreshingly different in appearance, if not colour, from the rather routinely styled black boxes we have seen everywhere for so long. Its acceptability in domestic surroundings would be determined primarily by its need for air (it must be adequately ventilated and nothing must be placed upon it), but if you are in the market for a well made, muscular yet sweet sounding amplifier and can do without the plethora of facilities it omits (but do many people really use the formidable array of controls still filled to many amplifiers?) then the A200 ought certainly to be on your shorllist of contenders.
