Preamplifiers — Dartzeel NHB-18NS

The NHB-18NS is the preamplifier of darTZeel, the Swiss manufacturer founded by designer Hervé Delétraz. NHB stands for not heard before and NS for no switches, a reference to the way the preamplifier selects inputs without placing any switch contacts in the signal path. It is designed as the partner to darTZeel's NHB-series power amplifiers, including the NHB-108 and NHB-468, and runs from a battery power supply.

Key specs that matter

Line gain is up to 11dB, and the MC phono stage offers 54 to 72dB of gain with loading selectable from 43 ohms to 47 kilohms. Input impedance is 50 ohms on the Zeel BNC inputs, above 30 kilohms on RCA and above 15 kilohms on XLR. Output impedance is 75 ohms on RCA, 50 ohms on the darT BNC outputs and below 600 ohms on XLR. Frequency response extends from 5Hz to 500kHz (+0/-1dB), rise time is below 0.5 microseconds and slew rate exceeds 24V per microsecond. Signal-to-noise ratio exceeds 92dB on line inputs, and crosstalk is below -80dB from 20Hz to 20kHz. The standard version has one MC phono input, four line inputs on RCA or Zeel BNC and one XLR input, and the chassis measures 440 x 335 x 170mm.

Engineering and use context

Instead of routing every source through a selector switch, each input has its own dedicated preamplifier circuit on a plug-in card, and choosing a source simply activates that circuit while the others are bypassed, under microprocessor control that sleeps when not in use. The circuits use no overall negative feedback, and the line signal passes through only eight silicon junctions from input to output, including a 13dB fully discrete gain stage, with three more junctions for the phono stage. The preamplifier is powered from an off-board lithium-ion battery, which isolates the audio circuits from the mains during playback. A full charge gives about eight hours of listening, with charging managed automatically. The darTZeel-specific 50-ohm darT and Zeel BNC connections treat the interconnect as a matched transmission line, avoiding reflections along the cable. Other factory configurations add a second XLR input or MM/MC phono stages, and phono versions include switchable subsonic and ultrasonic Neumann equalisation options. Aluminium parts are milled from solid blocks and hand-finished.

Pairing

The NHB-18NS is intended for darTZeel's NHB-108 and NHB-468 power amplifiers via 50-ohm darT-to-Zeel cables, but its RCA and XLR outputs drive any power amplifier. Three darT outputs allow bi-amping or tri-amping with simple built-in first-order filters.

Alternatives

darTZeel makes no other standalone preamplifier, the nearest model being the CTH-8550 integrated amplifier with a built-in preamplifier stage.