Solid State Preamp Reviews

DarTZeel Audio, the Swiss company dedicated to listening first and measuring later, has introduced a completely redesigned version of its battery-powered NHB-18NS preamplifier that is vaguely similar to the original in looks and in name. Based on its list price in Swiss francs and the exchange rate at time of writing, the NHB-18NS Mk.2 costs about $38,000.

I reviewed the original NHB-18NS ten years ago this month, in the June 2007 issue, and bought the review sample (it cost $23,250) without really thinking about its impracticality as a reviewing tool. The original lacked a volume control that could be set to a reference level; its optical-type volume knob just spins around and around, with no stops at the extremes of its range of effectiveness. I couldn't know where I was in terms of level, which meant that I was switching blind between inputs. That could be—and was—harmful to tweeters' health. Lesson learned: Think carefully through everything before buying anything.

Still, I didn't regret buying the NHB-18NS, despite its built-in moving-coil phono preamplifier's less-than-accurate RIAA equalization and the phono section's lack of adjustability (unless you were willing to open up the case and solder resistors to circuit-board pads), and the preamp's transformer-coupled balanced input and output, which had less than flat response. But I was going to use Ypsilon's VPS-100 phono preamp with the darTZeel and avoid the darTZeel's balanced connections.

What I loved about the NHB-18NS was its velvet-smooth yet well-detailed sound, as I described in my review—it bridged the gap between the sounds of solid-state and tubed preamps. Even the too-frequent battery charges, though a pain in the butt, didn't bother me too much.

The NHB-18NS Mk.2 solves all of the original's problems, and then some. It has a digital display on its front panel that shows the volume level in decibels; the balanced input and output are now active, not transformer-coupled; there's a new operating system I won't go into here, other than to say that you can now adjust the balance via the remote control; and the batteries have never run out of juice during a listening session, so the Mk.2 never once entered AC mode for the many months I've had it in my system.

The NHB-18NS Mk.2's new built-in MC phono preamp is sonically far superior to the original, and is more adjustable than many outboard models, particularly in terms of gain. You can select among gains of 57, 60, 63, 66, 69, and 72dB. The loading options are 43, 50, 75, 100, 150, and 300 ohms, or you can solder in your own choice. With a jumper, you can enable 47k ohms, but, as darTZeel's founder and designer, Hervé Delétraz, notes in an addendum to the manual, "Playing with 47k or no load using the 'bonus' setting gave more 'air' at first glance, however it was artificial." There's also a very useful subsonic filter, and a Neumann fourth-pole EQ option, both defeatable. (I switched off the Neumann fourth-pole filter for reasons previously covered). Unfortunately, I couldn't measure the accuracy of the NHB-18NS Mk.2's RIAA EQ.

The NHB-18NS Mk.2's built-in phono section is not the equal of the CH Precision P1 or the Ypsilon VPS-100 Silver Edition or other standalone phono stages. It's neither as transparent nor as dynamic as either of those named, but they are dedicated phono preamps that by themselves cost in the neighborhood of the darTZeel (the CH, at $31,000 without X1 power supply) or a lot more (the Ypsilon, at $65,000). However, the Mk.2's phono stage will more than satisfy casual vinyl listeners, and even enthusiasts who haven't been exposed to the best outboard phono stages might be happy: It produced no obvious additive flaws, while presenting well-organized aural pictures against impressively quiet backdrops.

Input options for the NHB-18NS Mk.2's phono preamp can be adjusted via a single toggle switch, under which are two rows of six LEDs each (since the preamp is dual-mono, there's one of these switches for each channel, directly under each phono input, all on the preamp's rear panel). The operating system is devilishly ingenious and, once you get the hang of it, easy to use—unless, like me, you don't have convenient access to the rear panel once the preamplifier is in the rack. In that case, it's difficult to impossible to adjust the phono input, unless you can at least angle the chassis out, after which you can use a mirror to see the LEDs. I tried my GoPro camera with iPhone app, which accepts the camera's WiFi transmission. I thought that was an ingenious idea, but the bright LED lights smeared on the screen; I ended up using a mirror. Still, it's a far easier arrangement than on the original NHB-18NS. I'm going to try using a filter on the GoPro's lens.

As on the original NHB-18NS, each input has its own module—there are no signal-routing contacts, switches, or relays. Selecting an input routes the signal directly to the volume-control module.

I'm not sure if the NHB-18NS's actual signal-passing circuitry has changed—it still has zero overall feedback, small amounts of local feedback at the inputs and voltage gain stages, and only seven transistors in each input module—but I thought its sound had improved.

With no loss of any of the original NHB-18NS's tube-like richness and generous flow, the Mk.2 seemed to better grip the music, which brought the rhythmic pulse closer to if hardly equaling that of Boulder Amplifiers' 2110 line preamplifier ($55,000), which I reviewed in the March 2015 issue.

However, the darTZeel's sonic purity and transparency have made it my reference preamplifier, especially when its signals are routed via its Zeel BNC 50-ohm, transmission-line BNC jacks to my darTZeel NHB-458 monoblocks. Today there are many great choices in electronics, and I've reviewed quite a few since buying the expensive NHB-458s ($144,500/pair)—but I'm done!

I wish darTZeel Audio had wider distribution in the US, so that more people could hear this stuff—especially those who can afford it.—Michael Fremer