Originally printed in the March 1995 issue of Gramophone.

NAD have quite a name for themselves, and a considerable number of friends, particularly amongst the student community, by marketing a range of high fidelity units, or 'separates' at very low prices. These units invariably offer a good, sometimes excellent, performance and are attractively styled so that they assemble into a viable alternative to the mass-market mini or midi systems of questionable quality, with the added advantage of personal choice in the selection of components. This they have achieved by harnessing UK design skills to the economies of manufacture in Taiwan. Although they also have upmarket items in their range, a £1,000 power amplifier for example, their forte lies in the no-frills, well conceived, straightforward and user friendly product area. However, their design team occasionally comes up with refreshingly novel ideas, often economi cally advantageous, and then proceeds to incorporate them successfully in new models. Such is the case with this 310 amplifier.

A 25 watts per channel integrated amplifier for less than £130, usually means a pretty skimped design, probably based around a single power chip and a stretched power supply; that is certainly not the case here. NAD have taken the currently popular path of omitting LP record preamplifier stages and have provided instead a pair of record and playback 3.5mm jack sockets on the front panel into which the owner can plug his Walkman, portable CD player, personal radio, MD or DCC, even TV or VCR if it has suitable outlets. That might be considered a money saving swap but it is a valuable one and right in line with the listening habits of today's progressive users. I suspect it will not be long before we see it accepted as current practice. The only other external evidence of manufacturing economy is in the omission of a headphones socket, but in most cases this will exist in the source equipment, particularly those of the kind listed above.

The front panel controls are minimal and straightforward. At the left is a green On/Off button, and inboard a small pair of knobs for the centre detented Bass and Treble controls, with a defeat button between them. Top centre are green and red LEDs, the former indicating power up and the latter lighting up if the protection arrangements are tripped by overheating, shorted loudspeaker leads or internal fault. Immediately adjacent are two more buttons, one to enable the front panel playback jack, so that the user can leave a source plugged in, and the second a Tape Monitor. Further along are four source buttons, all identical line-level selectors but labelled Video, Aux, Tuner and CD. Lastly there is the large, friction-coupled, dual concentric Volume knob. Rear panel connections are equally simple: just a twin row of phono sockets, four reasonably substantial loudspeaker terminals with 4mm centres and an attached two metre mains lead with plug.

The NAD 310 is constructed on a standard pressed steel framework fitted with small drum feet and has a thick, dark grey, plastics moulded front panel, with black knobs and buttons and white lettering. A folded, ventilated, sheet steel cover is retained by five bolts in sides and rear. On removal one immediately notices the fair sized toroidal power transformer and dual-channel, single-ended power supplies, independently fused; both unusual in budget amplifiers which commonly incorporate cheaper frame-type transformers and a single dual-rail supply. On the other side of a pair of vaned heat sinks which run centrally from front to back are unusual sets of power transistors, their legs slotted into the main printed circuit board. This is only lightly populated by other components, which include a couple of dozen transistors and no integrated circuits—all very unconventional. The reason lies in the development and adoption of a new power amplifier architecture which NAD have justifiably named Super Simple circuity.

For reasons of economy, nearly all popular transistor amplifiers operate in a mode called Class AB, which basically means that their current demands vary with the strength of the signal they are asked to handle. This in turn requires that they need push-pull driver and biasing arrangements which have become increasingly elaborate over the years since H. C. Lin came up with his classic semi complementary circuit in 1956. Previous to that, most designs used an inter-stage 0 154 Gramophone March 1995 transformer driven by an additional power transistor but this was costly and had limitations in the application of sufficient negative feedback.

Faced with a blank sheet of paper perhaps headed 'New Budget Amplifier', someone at NAD, blessed with lateral thinking, has realized that by using modern semiconductors it would be possible to retain the simplicity of the transformer drive arrangement, but permit the omission of the transformer. At this point I quote from their fact sheet: "(Previous) circuitry, being the most limiting factor, was disposed of, to be replaced with a single ended, pure 'Class A' driver stage. This in turn drives a complementary set of output transistors, one N channel MosFet and the other a state-of-the-art PNP bipolar transistor. Through careful and limited local feedback around these transistors their characteristics are accurately matched. The result is an amplifier with approximately half theumber of components and an increase in efficiency of almost 20% when compared to other amplifiers of similar price or specification. This reduction permits the use of higher quality cornponents ..." Faced with a novel circuit one tends to elaborate when conducting the usual performance measurements but there is nothing to suggest that this amplifier has such an unusual power stage, except perhaps that clipping at overload was slightly asymmetric, the positive peaks limiting before the negative ones. Clipping into 8 ohms loads occurred at 26 watts with an input of 225mV and with the mains standing at 240 volts and at 35 watts into 4 ohms. The frequency response, flat through the normal 20Hz-20kHz range, was only 1 dB down at 8Hz and 85kHz and 3dB down at 6Hz and 160kHz, a wideband design. Distortion at the onset of clipping was less than 0.1% and was mainly second harmonic. Crosstalk between channels was -60dB falling slightly to -50dB at 20kHz. Unweighted signal-to-noise ratio was only 76dB due to the presence of a mains harmonic riding above the background, which was some Specification 15dB lower. The tone controls are also unusual in that their effect is progressively removed as the volume control is advanced beyond 12 o'clock—not at all a bad feature, which prevents their abuse. At moderate volumes the bass control had a range of -6 to +9dB at 50Hz and the treble -6 to +6.5dB at 10kHz.

Experience tells us that it takes more than a fine set of measurements to guarantee equally fine sound although the reverse is certainly true. But the reader need have no doubts about this one. Unfortunately for us reporters of the audio scene it is also true that the better an amplifier is the less there can be to comment on— neutrality carries the day. It would be foolish to pretend that a £130 amplifier is perfect, although this one has pretensions in that direction, but its defects are mainly transient: was that hardening of Callas soaring into her upper register true?; did those loud organ pedals have quite such rich harmonics? Pianoforte sounded fine but string tone sometimes grated.

After the seasonal festivities had died down I took time to patch this 310 into my main system, which I like to think approaches the 'stateof-the-art', and make some direct comparisons. Not surprisingly, there would be something on many of my 'difficult' discs which would make me revert for a check, sometimes to be convinced of some minor problem but as often as not dismissing it as irrelevant.

This sort of performance at this sort of price marks another landmark for NAD. Ten or twelve years ago I would guarantee that you could climb any staircase in an Oxbridge quad and find some student's room boasting a NAD 3020 amplifier coupled to a Pioneer PL12 turntable and a nondescript and probably battered pair of loudspeakers, such was its popularity; for many it was the budget amplifier to own. NAD have certainly produced a worthy successor in this 310 and there can be no doubt that it warrants still wider public acceptance.