Stereo Amplifier

Review: Yamaha AX-592 Stereo Amplifier

There are three integrated amplifiers in the current Yamaha range, not counting its varied Home Cinema and Classic Line components, all reworkings of earlier models. The AX-592 (£279,95) heads the list and has a 2 x 100W power rating into 8 ohms. It is a fairly bulky unit, having standard base dimensions of 435 x 396mm but an above average height of 150mm (6in). It follows the current trend in being supplied with a remote handset, which conveniently provides armchair control not only of volume, via the motorized volume knob, but also of source selection (for which the rotary switch is similarly motorized and contains a built-in LED indicator) and Power On/Standby - with the power LED half illuminated in the standby mode. Incidentally, this same handset will work with appropriate Yamaha CD players, tuners and cassette decks and will even provide pickup arm raise/lower with a suitably appointed Yamaha turntable.

Somewhat against the modern trend, the AX-592 has a very full range of features - bass, treble, balance, continuously variable loudness and a subsonic filter which introduces an 18dB/octave slope at around 15Hz to attenuate turntable rumble, etc. There are also pairs of input/output sockets, normally linked, which separate the functions of the preamplifier and the power amplifier to enable an external graphic equalizer or other processor to be looped into circuit.

However, in recognition of the fact that routing the audio signal through this maze of extra switches can lead to signal degradation and problems with induced noise or interference, there are two bypass options. A Pure Direct switch gives straight-through routing for all input sources, assuming that none of the control features are required, and a CD Direct Amp switch actually engages a special preamplifier circuit dedicated to CD amplification and additionally bypasses the source selection switch.

The front panel has been designed to give an uncluttered look, with a nip-up cover concealing all controls except Power On/Standby, a headphones socket and Loudspeakers A/B selection on the left; Volume, Source selection, Pure Direct and CD Direct Amp switches on the right. One further knob, hidden behind the cover and not so far mentioned, is the Record Output selector which works independently of the setting of the main Source Selector and determines the source to be routed to the Rec Out sockets, allowing the user to record from one source while listening to another.

Casing construction is fairly standard, with a wrap-round metal top and sides and a more substantial contoured fascia block. The top panel is perforated for improved air circulation but I am bound to say that the unit ran cool during many hours of continuous use. Obviously nothing should be placed on top of any high-power amplifier which might impede ventilation.

The internal layout has the expected logic and a strict adherence to L/R channel symmetry. Power supply is located hard left, behind the Power On/Standby switch, and is based around a larger than usual mains transformer and substantial smoothing capacitors. The audio circuitry has a neat symmetrical plan with front-to-back arrays of vaned heatsinks framing a large printed circuit board, above which straight-wire connections carry the signals to the loudspeaker outlets. The component s associated with the tone controls and filters are grouped on a subsidiary strip immediately behind their respective knobs. Yamaha calls its version of this signal-preserving topology ToP-ART (Total Purity Audio Reproduction Technology) in which left and right channel circuit symmetry is combined with straight, minimum length signal paths.

It also gives emphasis to the need for large amounts of reserve power to accommodate the transient peaks associated with digitally recorded signals and has even provided a loudspeaker impedance changeover switch for best matching to 4 or 8 ohms rated loads. A linear damping circuit maintains a constant (low) output impedance giving a stable damping factor of about 320, thus minimizing the (admittedly small) response variations caused by frequency-dependent changes in the loudspeaker impedance.

The rear panel is moderately congested in appearance with pairs of input sockets for the various sources: CD (gold-plated), Phono (with a changeover switch alongside for moving-magnet or moving-coil sensitivity and an Audio earth terminal), Tuner, Auxiliary, Tape 1 and 2. Output sockets are provided for Tape 1 and 2 plus the linked pre/main sockets previously mentioned. Different types of terminal are used for loudspeaker outputs A and B, neither suitable for use with 4mm plugs. The A terminals have an extended insulated slot for extra safe insertion of bare wires, while the second B pair are of the more conventional binding post variety. Alongside these is the loudspeaker impedance selector switch, a switched AC mains outlet for use with an associated component, and a captive 1.5 metre, two-wire mains lead terminated in a mounded three-pin plug. Note that the headphones socket on the front panel has no separate volume control and it will be necessary to switch off loudspeakers A and B when headphones-only listening is required.