darTZeel NHB-18NS preamplifier Page 2
The proprietary volume, or Enjoyment, control uses no contacts, relays, switches, or silicon devices. DarTZeel isn't talking about its exact methodology, saying only that "some light is involved." Like all optical volume controls, this one keeps spinning as you turn it. The volume gradations were extremely fine—there are 192 of them in 0.5db steps, with a precision of "about plus or minus 0.2dB, closer to 0.1dB at typical listening levels." At no time did I ever wish for a volume level between two positions. If you turn the Enjoyment knob too quickly, it won't react, in order to prevent large, sudden, speaker-damaging increases in volume.
The built-in phono preamplifier's factory default settings are for moving-coil cartridges, 60dB gain, and 836 ohm loading. A 1nF cap is included to squelch incoming RFI from the cartridge. Owners who know how to use a soldering iron can set the phono gain between 30 and 66dB and adjust the loading via "solder pads." (How this is done will be spelled out in the forthcoming manual.) Moving-magnet cartridges can also be accommodated, though there are no capacitive loading options—according to designer Hervé Delétraz (darTZeel is an anagram of Delétraz), modern MM cartridges no longer require adjustable capacitive loading, and phono cables usually add the right amount. I doubt anyone buying an NHB-18NS will be using an MM cartridge—not that there's anything wrong with MMs.
The NHB-18NS functioned smoothly and without glitch throughout the entire review period. My only complaint was the remote-control receiver's narrow reception window. I had to point the remote directly at the preamp; even the slightest deviation from dead-on-axis resulted in no communication at all. Fortunately, the central LED glows green when the remote and receiver are communicating. DarTZeel is working to improve the remote's off-axis performance.
Circuitry, or lack thereof
Hervé Delétraz first showed me the NHB-18NS in prototype form at London's Heathrow Hi-Fi show in fall 2005. He removed the cover and ran me through many of the dual-mono design's elements, including the bank of four large batteries and 12 vertically mounted parallel circuit boards—one each for the six inputs per channel. The main board, which is mounted to the chassis bottom, accepts input signals via ribbon cables and connectors. Modern surface-mount technology is used throughout. There appeared to be nothing old-fashioned or retro about the circuit design, nor did there appear to be any unusual components, such as capacitors the size of toothpaste tubes. The NHB-18NS's interior build quality is commensurate with its exterior.
When Delétraz, who has a degree in electrical engineering, again summarized the design for me in preparation for this review, its unique, minimalist nature became more apparent. The NHB-18NS's fully dual-mono design extends to both the battery and AC power supplies, as well as to the signal and ground paths. It uses no global negative feedback, not even in the phono stage, and no op-amps in the signal path. The claimed bandwidths of 1Hz–1MHz, +0/–6dB, and 10Hz–100kHz, +0/–0.5dB, are ultrawide, for zero claimed phase shift.
"For the first time in all audio history," said Delétraz, "the signal path does not pass through any physical switch, relay, or even transistor switch." Instead, inputs are enabled or disabled using electro-optical analog components. Because there is no physical input switch or FET-based analog switch, there is no "diode effect," either electrical or chemical (electrovalence differential), to alter the signal, he explained in an e-mail.
All of the audio circuits are "directly scaled down" from the patented NHB-108 power amplifier, with minimal numbers of active components in the signal path, all of them discrete, bipolar transistors. The signal passes through only seven transistor junctions from input to output in the line stage, which provides 11dB of gain (5dB using the 50 ohm darTZeel connections).
The phono stage incorporates two gain circuits using eight discrete junctions in the signal path. RIAA equalization is passive and includes the fourth "Neumann" pole (3.18µs/50.048kHz) to ensure accurate high-frequency reproduction.
The chassis is CNC-fabricated from raw aluminum plates and billets, then hand-brushed and -anodized inside and out, then precision-adjusted with cogging pins, similar to watch construction (it's made in Switzerland, after all).
According to Hervé Delétraz, his goal was to create a preamplifier with maximum transparency, low noise, a subjective sensation of relaxation, and a coherence of rhythm and pacing resulting from, among other things, the "elimination of phase shifts at the frequency extremes."
Straight wire with gain?
Should a preamplifier be merely a traffic director, controlling the rate of signal flow and routing signals along chosen pathways while remaining neutral about what's passing through the pipeline? Or should it also impart a pleasing flavor to the proceedings?
These questions, long debated among audiophiles, are a waste of time, in my opinion. Anything inserted into the signal path will change the sound, even a passive volume control—especially if it's unbuffered. Those who seek some mythical "sonic purity" should probably give up audio and join a monastery.
Any audiophile who's bought a tubed preamplifier has decided to impart a particular sonic flavor to the proceedings. However, the same can be said of those who prefer solid-state preamplification. The conflicted choose hybrids of both technologies, such as my reference Musical Fidelity kWP. Whichever technology you choose, it should at least be quiet, dynamic, wideband, linear, and produce a low level of distortion. Both my listening and John Atkinson's measurements confirmed that the Musical Fidelity kWP, which isn't exactly inexpensive at $11,000, easily met those criteria (see Stereophile, December 2005), as did the three-box, $26,000 McIntosh C-1000, which I reviewed (and loved) for the August 2006 issue.
I haven't yet seen the NHB-18NS's measurements as I write this, but having listened for a few months, I don't doubt Delétraz's claim of quiet, dynamic, linear, wideband performance with low distortion (though the "less than 1% THD" spec isn't all that low). While 11dB isn't a great deal of gain, it proved more than sufficient when paired with any of the associated power amplifiers. No output impedance is specified for the unbalanced outputs, but based on my listening, especially comparing darTZeel's proprietary 50 ohm darT and Zeel connectors with standard single-ended types, it should measure sufficiently high to create no problems for most amplifiers.
Yet switching to the darTZeel NHB-18NS from the MF kWP produced profound sonic changes in my audio system, almost all of them much for the better, at least subjectively.
On first hearing, the darTZeel immediately revealed itself to be stunningly transparent, giving my Wilson Audio MAXX 2 speakers an electrostatic-like top end. Transient speed, resolution, and decay were nothing short of spectacular from day one, and that particular window on reality still retained its grip on my listening experience months later.