Listening #63 Page 2
"If you could look at the circuit in three dimensions," Morecroft says, "which is in fact how it's designed, you'd see that the signal circuit as a whole is twisted toward the front of the preamp. We want to keep the attenuation stage very close, physically, to further avoid degradation."
In common with other high-quality preamps, all of the DNM's gain stages are supplied on removable sub-boards; in common with nothing else I've seen, the 3D's gain-stage boards are double boards, designed and built symmetrically: Each channel's line and phono amps exist as back-to-back double-differential boards. (Sockets are provided for two sets of phono inputs, configurable as any combination of moving-magnet and moving-coil cartridge and selectable by means of a front-panel toggle switch.) The circuit pathway spacing within the DNM 3D never deviates—which is remarkable.
The line amps are especially interesting. For one thing, according to Morecroft, the boards are designed to be mechanically better than their predecessors, For another, Morecroft says he configured them with "a very high line-in impedance and quite a good drive capability—so much so that the line amp can drive headphones now. Hence the socket." Like most DNM preamps, the 3D uses separate ground conductors for the left and right channels—their DIN connectors use pin 4 for the extra ground—but because headphones use a common ground, Morecroft was forced to follow suit in the wiring of his headphone jack. When the jack isn't being used, the left and right grounds remain split.
The phono selector switch and headphone jack aren't the only new additions to the front panel: A small, two-position toggle switch is snugged between the volume controls, with the left position for stereo output and the right for true, living mono—hallelujah! "I actually wanted a third position, for 'nearly mono,' but I was discouraged from doing so," Morecroft laughs. Back in May 2004, I wrote that I loved the DNM preamp's dual-volume control scheme but wished it had a mono switch. Today I love the DNM preamp's dual-volume control scheme and mono switch, but wish I were charming and had all my hair back.
Finally, while you wouldn't think it's much of an issue in a domestic preamplifier, the DNM 3D also embodies Denis Morecroft's evolving ideas about the implementation of negative feedback: "Not long ago we tested a PA3ΔS amp against a Cary single-ended-triode amp. For all the strengths of our amp, when we did the A/B comparison, we could still hear a 'calmness' in the high frequencies that the no-feedback Cary had. We started looking into it, and discovered that the feedback circuit of the [DNM] amp was compromised by all of the various 'ports' and their impedance reflections. Feedback is not itself bad, but it interacts badly with the impedances of the connections, to produce a harsh effect. We've got definite evidence that this is going on."
The answer, Morecroft says, is in reducing the amplitude of the reflection effects through the use of tiny capacitors and resistors—combinations that Morecroft refers to as terminators—at various signal connections within the amp and preamp. "When we did our testing, we ran it against a chassis that didn't have the termination components installed, and that convinced us we were on the right track. We had found the degree of calmness we were aiming for."
And that brings us to one more change in the DNM product line: The company that introduced solid-core, ribbon-style speaker cables to the world of domestic audio has released its first new cable since 1984. Like the previous DNM speaker cable, their new Stereo Solid Core Precision speaker cable ($12/foot per pair plus termination) uses a single solid wire for each conductor, molded into the dielectric such that the positive and negative runs are spaced precisely and consistently from one another. The new wire goes a step further and molds the four conductors required for a stereo system (or one biwired channel) together, side by side—for even greater control over spacing and, consequently, electromagnetic interference with the audio signal.
Concert Sound supplied me with a 5m run of Stereo Solid Core Precision cable (henceforth known as SSCP), terminated with low-mass Eichmann Bayonet bananas at the loudspeaker end of the ostensibly directional cable, and the gold-plated mini-bananas used on DNM's power amplifiers at the other. The stuff was easy to use: The idea is to route the whole four-conductor cable from the amp to the most distant loudspeaker, then to "unzip" the unused pair of conductors back only as far as needed—typically, to a location midway between the two speakers. The ribbon jacket is molded with a distinct crease that acts as a perforation to make unzipping neat and easy—and, as Denis Morecroft suggests, possibly reduce the Q of the cable jacket.
Compared with the only other cable I have in house that was both long enough for the installation and capable of being pressed into service with mini-banana sockets—a run of Nordost Flatline from which, for some long-forgotten reason, I'd removed all connectors—the SSCP allowed the DNM amplifier and the Quad IIs to sound ever so slightly smoother, with a not-so-slight improvement in spatial focus. On the other hand, although I admit that I expected to like the new SSCP cable with my Shindo Cortese amp and Audio Note AN-E loudspeakers, I didn't: The DNM cable was smoother than the Auditorium 23 stranded cable I normally use with that combination, but it was too smooth for my tastes, sounding a bit uninteresting and lacking in texture. Like so many other exceptional cables, the DNM cable is potentially superb but undeniably system-dependent.
Back to the combination of DNM amplification and Quad ESLs (which, by the way, are among Denis Morecroft's reference loudspeakers): While audio reviews tend to concern themselves with immediately audible strengths and failings—the tuneful bass, the irritating grain, the dynamic compression that seems to agitate our wives from the next room—the DNM-Quad combination defied that approach. Not only is it difficult to express the strengths of these products by citing a litany of listening examples, it's darn near impossible to describe them at all.
What it all comes down to is this: I found that I could listen to my Quads for much longer chunks of time, and give fuller attention to reproduced music, with the DNM gear in my system. That was true with either the DNM or the Quad power amps in the system, as long as the DNM 3D preamp was driving them: Beyond that, it was just a matter of flavors—the DNM amp being more airy, pellucid, and spatially convincing, the Quad amps being more tactile and, believe it or not, grunty.
Another intangible: I simply enjoyed using the DNM. I loved the controls, the styling, the whole idea of the thing. It looks especially fine on a shelf full of books—not just any old crap, but good books—and the DNM logo is now so cool that I suspect it will never again be uncool, as it seemed to me just a few years ago. Sometimes I forget how to operate its various unlabeled controls—the whole idea that the mode-selector switch is left for stereo and right for mono sometimes throws me for a loop—and I still have a hard time remembering that the preamp is muted when the lights are lit, and functional when they're dark. Which, when you think about it, makes more sense than the other way around: Lights make light, but they also make noise.
Another imponderable: Beyond the most utilitarian considerations, why does anyone want to own anything? For that matter, why would anyone, apart from audiophiles and collectors of cichlids, mollusks, and aquatic plants—an especially nasty bunch—feel compelled to make you explain or defend why you like a particular table, or radio, or preamplifier? (Actually, I think I know the answer already: Those people are just angry that aesthetic impulses can't be measured, so they'd rather we didn't talk about them.)
Nostalgist though I am, I'm indifferent to the memory of my parents' old kitchen table—I don't have much capacity for kitsch, I'm afraid. But the notion of finding that old radio holds tremendous appeal for me. The DNM 3D, for its part, falls squarely on my want list.