The unit is of standard 430mm width and modest height. Its front panel controls and indicators suggest a fully specified design and a closer examination shows that the only practical omission is provision for low-output moving-coil pickup cartridges. As these can easily cost more than ten times the price of this amplifier perhaps it is not a very serious omission!
Other makers have chosen to adopt minimalist designs devoid of tone controls or phono stages in order to meet price constraints but Technics, probably rightly, has assessed that first-time buyers and the financially stretched might go for the extra facilities they have on offer. Certainly this amplifier is remarkable value for money.
As is common practice these days, once plugged into the mains via the detachable 1.5 metre lead supplied, the amplifier rests in a Standby condition which is indicated by a tiny red LED. A few seconds after operating the Power push-switch this changes to an adjacent Operation LED (which is also red though surely it should be green for go). A gold-plated headphones socket is fitted and alongside it two buttons, also with red LEDs, which operate relays to engage two pairs of loudspeaker connections. Following on are three small knobs for Bass, Treble and Balance adjustment and these have accurate centring detents. In addition there is a Tone Defeat button which bypasses them completely. The large central knob controls Volume via a high-grade attenuator which has been the subject of considerable research into materials and construction to minimize noise and distortion. Six large square buttons operate relays to select from four sources - Phono, Tuner, CD, Aux - plus two Tape inputs. Both of the latter can be monitored via a small sequencing button above and all settings are indicated by accompanying red LEDs.
At the rear are eight pairs of phono sockets for the above, a ground terminal for a turntable, four pairs of substantial loudspeaker terminals and the miniature mains connector already mentioned. Alongside the latter is a circular outlet for the small cooling fan which operates at high power output levels only.
The Technics SU-A600 is built on the usual plated steel tray made up of individual pressings - some of them quite elaborate; this tray then slots into a heavy mineral-loaded plastics moulding some 10mm thick which Technics calls a hybrid construction base. The intention is to isolate the entire amplifier circuit board and power supply from mechanical vibrations; the unit stands on the usual shiny drum feet. The ventilated steel cover is painted in satin black.
The front panel is contoured quite attractively. It is formed of aluminium, also painted black (as opposed to the more usual anodizing) and carries neat, readable legends. Internal layout has the hefty 'R-core' power transformer at the left with a deeply vaned extruded aluminium heatsink running from front to back alongside it. This carries four specific moulded power integrated circuits which comprise the MOS Class AA output circuit, the two MosFet driver stages being nearest the panel and the bipolar current sources towards the rear. Much of the remaining electronics is on a single large printed circuit board which occupies just a little more than half the floor area. Subsidiary boards are located behind the front panel.
Internal examination shows some of the improvements which justify the Mark 3 designation. The volume control I have already mentioned but there are new resistors with improved temperature stability, copper film capacitors with lower self inductance and, perhaps most significant of all, the new electrolytic capacitors using a special bamboo fibre called "Take" (pronounced ta-keh) as the separating layer.
Performance
Measurements soon confirmed that this Technics SU-A600 is no also-ran in the amplifier stakes. The mains supply in my area is usually on the high side and on the day in question was resting at 242 volts, so I found it possible just to squeeze 50 watts output from both channels at the onset of clipping, this into 8 ohm resistive loads. Most surprisingly it happily continued to do this over the whole useful audio frequency band from 20 to 20kHz. An input level of 170mV was required (at any of the line-level inputs) to produce this figure but the specified 150mV duly produced the 2x37 watts specified. By modern standards this is not a wideband design but it achieved perfectly adequate -1dB points at 4Hz and 27kHz in the lone defeat mode. Admitting the tone controls produced a small drop of 0.8dB in overall level and, with the controls centred, a slight roll-off above 5kHz to -1dB at 20kHz. Their range was pretty much as stated, as were all the other details; a most satisfying result.
So we come to the important question of how the Technics SU-A600 sounds, to which one can give the vague answer: musical. No one would pretend it to be the equal of some of the expensive landmark designs but it has a jolly good stab at it. On most material it is quite transparent and admirably listenable all the way from piano to forte. Complex passages, particularly full orchestra with choir, showed occasional thickening and a cathedral organ recording was several times cut up by the sheer weight of pedal notes. But at five pence below £200 one can but marvel.