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And what separates the Reference 18’s design from other class-D amplifiers?
"Fundamentally the Reference 18 shares the same amplifier technology with the Ref 9V3SE. The technology difference between NuForce and other class D amps can be summarized as having a higher switching frequency, featuring instantaneous feedback and error correction and very low phase shift due to our unique self-oscillation design which does not utilize a pulse-width modulation clock. NuForce owns its patented technology and controls the design and production of every generation of products where many other class D amplifiers utilize off-the-shelf modules from ICEpower, TI, Hypex and others. This allows us to make improvements at any level and stage of the design."
The specs for the Ref 18 are very similar to those of the Ref 9SE V3 - a claimed 175 watts RMS into 8 ohms and 335 watts into 4 ohms. Frequency response is quite wide at 20Hz -0.3dB to 120kHz at -3dB. Gain has been kept reasonable at 21dB to make for good matching with high-gain preamplifiers unlike some of the competition and their outrageously high-gain amplifiers (a bug bear of mine). Input impedance is a moderate 22K but higher would be better. The solidity of the chassis and larger power supply make for a solid unit that weighs 16 pounds (reasonably weighty for a class D/SMPS design).
Changing reference As already mentioned I’ve had the pleasure of reviewing a number of reference amplification products from NuForce. With each new version the company has managed to wring sonic and technical improvements. No different here. The Reference 18 is a clear upgrade from its Ref 9 precursors.
Based on my extensive long-term experience of owning the superb Ref 9SE V3 the differences are mainly in a sense of added refinement and texture in the midrange and treble. Almost incredibly—the Ref 9s already were champs here—the background is darker. Notes emanate effortlessly with taut transient attacks and decay with a trail of extended harmonics. This inter-note silence somehow creates in the listener a perception of the lower notes being made of tighter ‘stuff’ and of the midrange having an overall smoother more liquid and tonally richer nature.
There’s also a sense of utter control where the music oozes with ease, with an ebb and flow that delivers a continuity of pace and adroitness which communicates the inherent rhythm and musicianship. Another immediately noticeable improvement is the depth of the presentation like a layered cavern of almost no frontiers. Sera Una Noche’s "Quedemonos Aqui" showed a stage of truly magnificent spread (no change there from the Ref 9) and enormous depth (definite improvement there). The bells, percussion and bandoneon were rich in texture, extended in harmonic detail and precisely separated within the busy mix.
I’ve been lucky to have auditioned a number of products within my system of late that have displayed a sense of ease and effortlessness—the Berkeley DAC I’m reviewing for another publication comes to mind immediately—which allow the enjoyment of music without being subconsciously on edge like when the anticipation of a crescendo arouses fear to result in hardness or vocal sibilance that might be piercing. The Ref 18s also allowed this type of enjoyment without the under current of stress.
