The DarTZeel NHB-18NS Preamplifier

Of all of the components that make up a hi-fi system, experience shows that it is the pre-amplifier that presents the biggest enigma. The task it has to perform is, in theory, pretty straightforward; directing the signal from the desired source component and controlling the volume. Compared to the process of extracting information from the reflective surface of a CD or the groove of an LP, or driving massive amounts of power into a loudspeaker whose job consists of converting electricity back into recognisable audio, it should be a walk in the park. Its not even as if there is any gain needed, as the output from an average CD player is more than enough to drive most power amplifiers into clipping. Hence passives, although in the real world, considerations such as input/output impedance and the capacitance of the cables hinder the attainable performance, while active circuitry provides a degree of isolation and stability against such effects.

Why then, am I so often forced to conclude that the pre-amplifier is the defining component of a systems ultimate performance. And, while the limitations of a poor source component or compromised power amp/ loudspeaker combination are relatively easy to identify, the pre-amp often seems to be a constriction or compromise to sound quality that manifests itself in a far more subtle way. Of all audio components, the pre is the one that we expect to be the most sonically pure and devoid of character, adding nothing while acting as the ‘gateway’ for the system that everything else connects to. And the truth is that for all the interesting and highly competent audio equipment I have auditioned in a system at home, the number of truly great pre-amps that have left a lasting impression can be counted on the fingers of one hand. The NHB 108 power amplifier was the first product to appear from Swiss based daRTzeel. A 100 Watt per channel design that was the embodiment of simple, elegant and beautifully symmetrical circuitry, it had a build quality and attention to detail second to none. It also sounded staggeringly good. I was therefore only too happy to have it back while auditioning the 18NS pre-amp, which is built as you might expect, in much the same fashion. Imagine Swiss watch precision applied to virtually every aspect and you begin to get the picture; attention to detail and refinement is the order of the day. Aesthetically the daRTzeel is quite conventional in its shape and mechanical construction, but the metalwork is finished in an industrial red anodising with a mustard gold front panel (which incidentally is much darker than the power amplifier) and I guess this is a look that you will either love or hate – me, I’m making no comment. Further enhancing the ‘glitz’ factor is the gold plated nameplate that you send back to the manufacturer to have engraved with the serial number and your name once you have purchased the unit. Front panel controls consist of a power button, small toggles for mute and mono (hurrah!) and two rotary controls for input selection and volume that are labelled ‘Enjoyment Source’ and ‘Pleasure Control’. A sense of humour lurking under the serious exterior?

Internal construction is about as good as it gets, using selected components and no less than twelve input boards on which the connectors in one of the neatest Finally, three multi coloured Led indicators indicate the status and operating conditions of the pre amplifier. The 18NS has four single-ended line-inputs together with one balanced; the RCA’s are duplicated by (darTZeel’s proprietary) 50 Ohm BNC’s and there is a phono input; yep, the darTZeel has a fully fledged phono-stage on board, a trend that seems to be returning. Outputs consist of the usual fixed level tape, balanced and RCA options, augmented by three separately buffered BNC’s specifically for the 108 power amp (the instruction manual talks of incorporating filters for bi or tri-amping at a future stage).

The electronic design has a number of interesting aspects and some shared philosophy with the power amplifier. Thus the circuitry employs a simple, symmetrical configuration utilising discrete components (rather than op-amps) where the signal passes through only six transistors in the main gain stage. This delivers an impressively wide bandwidth, claimed to be within 1dB from 1Hz to 1MHz, with no overall feedback applied. Each input has its own dedicated gain stage, which remains permanently connected and is activated when required, thus avoiding any kind of switching in the signal path. Likewise, there is no potentiometer or resistor network in line with the audio, volume control being by passive attenuation governed by a dedicated processor via analogue optical couplers, offering 192 steps in increments of 0.5dB. This leaves the volume knob whirling like a dervish to make any ground, while the remote rather over compensates with sudden lurches up or down. Acceptance angle is narrow but otherwise it is a simple, tactile handset (unlike so many others). For once the balance control is subtle in action, rather than swinging wildly left and right. The phono-stage follows similar design criteria to the linestage, utilising discrete components to provide 60 db of gain, although both this and the loading are internally adjustable using a soldering iron; good for sound, bad for convenience.