NUANCE PREAMPLIFIER It T HAT audio occupies such a I special niche in the corner of the electronics world is perhaps surprising in view of the outwardly straightforward and certainly readily defined basic requirements that have to be met. Ever since valves replaced the early acoustic playback machines, even the most able design engineers have argued over this or that aspect of circuitry. One example is pickup equalization and the plethora of circuits which have been conjured up to manage it, each claiming a particular superiority beyond its taken-forgranted ability to correct for the curve generated by the three time constants of the basic RIAA curve. Whereas in most other branches of electronics today the basic design objectives completely describe all that needs be expected of a circuit, in audio the adequacy of the objectives themselves seems often to be open to question. The ear, though readily persuaded, is not easily convinced.

One designer who is at the centre of a lot of controversy at present is Dr Malcolm Hawksford of the University of Essex. Amongst many other things, he has applied. himself to the problems of extracting the best performance from moving-coil .cartridges. Because these devices routinely operate at voltage levels of only a few tens of nanovolts, the signal itself is particularly vulnerable to the nonlinear effects of diode junctions, metal-to-metal contacts, soldered joints, etc. Hawksford terms this kind of degradation "Fuzzy distortion" and has set out his thinking in an eloquent, if largely impenetrable, paper in the Journal of the Audio Engineering Society (Vol 31, No. 10, October 1983). His own design for a preamplifier which overcomes these limitations has now reached commercial fruition in the form of the French-made Famco "Nuance" preamplifier which is the subject of this review.

Features and circuit

From the preceding paragraphs it will be clear that the first concern of the Nuance preamplifier is to optimize the.performance of moving-coil cartridges and to that end the unit has a dedicated MC/RIAA stage rather than the usual arrangement of a separate R1AA circuit which can handle either the output of an MC gain stage or the direct input from a moving-magnet cartridge. Two versions of the preamplifier exist, therefore—the one under consideration here which is for moving-coil and a less expensive version for movingmagnet.

This MC model comes in two boxes, one for the preamplifier itself and one for the power supply (the MM version fits, conventionally, into just one box). The power supply houses the mains transformer, rectifiers and initial smoothing circuitry and also carries the mains on/off switch. The idea of keeping all this apart from the preamplifier itself is to isolate the deleterious effects of stray electromagnetic fields and mainsborne interference from the very low level signals circulating in the MC stages.

The facilities of the Nuance are frugal in the extreme. The front panel carries three toggle switches for input selection and two rotary controls for volume (stepped) and balance (centre indent). No tone controls or HF tailoring filters are fitted. In addition to the phono pickup there are just three other inputs denoted tuner, tape and monitor. For clarity I would have preferred it had the tape been labelled auxilliary or CD and moni tor called tape monitor (which is what it is), so that a recording would be made from any one of three inputs with the option of monitoring the recording while in progress if a threehead tape deck is in use. The rear panel carries six pairs of phono sockets (with a locking option if appropriate plugs are to hand), the phono pair being gold plated. A ground screw is located adjacent to these.

Internally the unit is dominated by an extraordinarily large array of capacitors (well over 70 in all, many of them used for supply decoupling and RF filtering) all laid out with discrete transistors, integrated circuits and resistors, etc., on a large fibreglass printed circuit board. All components are top quality (1% metal film resistors, polypropylene and polycarbonate capacitors, Noble potentiometers, gold-plated contact toggles, and so on) and the layout is very neat. Output gain can be adjusted via plug-in resistors (supplied) so that the overall system level can be set up to make best use of the range of the volume control. An internal toggle switch sets the — 3dB LF rolloff point at either 2Hz or SPECIFICATION (Test Results in brackets) Maximum output: 15 Volts (agreed)

Total harmonic distortion: less than 0.05% at 2 Volts (0.03%)

Signal-to-noise ratio: line 85dB (86dB, 102dB weighted) pickup 58dB (62dB)

Input sensitivity: MC pickup 0.2mV (agreed)

Frequency response: RIAA/IEC within 0.2dB (agreed, see Fig. 1) 3dB bandwidth: 2Hz to 150k Hz (2Hz to 180kHz) Dimensions (W x H x D): 410 x 66 x 225mm Weight: 4.4kg

Manufacturer: Famco, Paris, France

UK distributor: Presence Audio, Eastland House, Plummers Plain,

Horsham, West Sussex, RH 13 6NY

UK retail price: £695

Phono equalization compared with new IEC Standard 20Hz, the former being preferred but the latter helpful for use with ported loudspeakers or in situations where acoustic feedback is a problem.

One novelty of the phono circuit is that its gain is inherently self-adjusting, so that it can cope with a wide range of cartridge impedances and sensitivities. Minimal feedback is used together with passive RIAA correction to achieve a wide bandwidth with low HF distortion. An arrangement of so-called star earthing helps keep the signal path particularly 'clean'. At switch-on the outputs are grounded for some 10 seconds to allow the circuits to stabilize, avoiding audible thumps and clicks through the loudspeakers. A front panel LED flashes while this mute is in operation. The cabinets are fabricated from a combination of aluminium (chassis and over-large anodised front panel) and steel (cover). Visibly the effect is rather plain but functional looking. There is a choice of champagne gold or black for the finish.

How it performed

The Nuance comfortably met, and in several cases well exceeded, its specification on John Borwick's test bench (see Table and RIAA response graph). The measured output impedance is low at 233 Ohms, which means that a long pre-power amplifier lead can be used with equanimity if required. Something to make many design engineers shake their heads in incredulity is that Famco advocate switching on the unit at least half-anhour before it is required to enable the circuit, particularly the electrolytics, to warm up and perform optimally.

Extravagant claims are made for the sonic purity of this preamplifier and I must say straight away that in my own system (using on this occasion a Dynavector Karat 17D moving-coil cartridge) the results were really first class. The clarity, the ease with which it was possible to delve into the various musica strands of a recording, was truly exceptional and the stability with which the stereo sound stage was projected regardless of the level or transient content or the programme material quite remarkable. Residual background noise was just apparent at the speakers with the gain set for normal listening, but quite inaudible back at the listening position where it matters. I have heard quieter but this is certainly quiet enough. Similarly exemplary results were to be had via the line level inputs, most notably when listening to Compact Disc or live Prom broadcasts. Here the Nuance is completely 'transparent' with, of course, the noise floor so low as to be completely inaudible.

This level of performance has to be weighed against the very high asking price of £695, which, believe it or not, actually compares very favourably indeed with some of the more extravagant exotica, particularly imported, available at the very top of the market. For most users, of course, and I certainly include myself here, it is a great deal to pay for so few facilities and inputs. That said, however, it certainly deserves consideration by anyone assembling a cost no object, 'super-fl' system and can be recommended in that context. For those who prefer to remain with moving-magnet cartridges the MM version of the Nuance retails at £495. As a point of interest Famco also makes a matching power amplifier, the Plenitude, which is rated at 80 Watts • into 8 Ohms and costs the same as the MC Nuance.

IVOR HUMPHREYS.

POSTSCRIPT

Concern has been expressed over the Nuance power supply, which on models brought in so far has not entirely satisfied the stringent UK safety regulations. Presence Audio assure us that all units now on sale are being modified accordingly to bring them into line in this respect.