Listening #16 Page 2

Then there are DNM's signature acrylic enclosures, which Morecroft began using in 1984. Prior to that, the very first DNM electronics were housed in steel enclosures—"strikingly beautiful things," he says, "which were made for us by some very nice people in Rayleigh, Essex." But when Morecroft applied himself to banishing nonessential conductors from his products, the move to a plastic case was inevitable.

Having the acrylic pieces manufactured in England with the degree of precision he required proved impossible, and Morecroft wound up having the work done in Switzerland. (In 1991, all of DNM's manufacturing was handed over to a Swiss firm, Karlev/Reson, initially because the Swiss market wanted more DNM products than the tiny English company could actually make.) Those plastic boxes may lack grunt appeal, but their value in the war against distortion is obvious: DNM has now progressed to where even the fixing screws in their casework are made of plastic.

"I know some engineers find it difficult to accept that metal could be a problem. But things go a lot deeper than they realize..."

Deep enough that Morecroft came to reject off-the-shelf capacitors as unsuitable for DNM's preamps and amps: While other designers were busy looking for the best-sounding caps—a noble enough goal in itself—he set out to design his own. The first result was the slit-foil capacitor, a signal cap named for the series of small incisions made in the conductive layers prior to assembly in an effort to break up and prevent the formation of eddy currents.

An arguably greater stride came with Morecroft's invention, a few years later, of the T-Network capacitor, a power-supply cap sporting four electrical terminals instead of just the usual positive and negative. In the T-Network cap, the two plates are tapped not only at their ends but at their centers as well. (Hence the name: picture one of the plates as the top of a letter T.) This construction detail helps to guide the current toward separate input and output sides of the capacitor, eliminating the resistance between the charging current terminal and the outgoing current terminal, which otherwise results in unwanted voltage (that pesky Ohm's Law again). With the resistance shunted away from the "throughput," the capacitor is allowed to work more or less purely as a capacitor, giving more effective filtering, particularly at high frequencies. DNM's T-Network caps are manufactured in England by BHC, and Morecroft says they've already been adopted for use by Rotel and other prominent audio manufacturers. (DIY enthusiasts are welcome to make inquiries by writing to Denis; put "T-Network" in the Subject line.)

Notwithstanding his satisfaction at seeing a DNM invention adopted by other audio companies, Morecroft hesitates to place too much importance on individual parts. "I think it's a point worth making that many of the effects that we hear in amplifiers, and that we attribute to inserting this or that new bit, don't really have anything to do with the new part but rather with the fact that the new part has altered, in some way, the manner in which the amplifier functions as a whole. As an example, one of the things we've observed with the T-Network capacitor is that, while it improves the filtering—and that's certainly good—it also changes the overall impedance of the power supply. That itself can even change the open-loop gain of the amp, and some listeners will hear a difference that's associated with that.

"It's much the same with cables, isn't it? Now we have an industry that's gone horribly wrong—horrible because people are spending millions of dollars on these products—and it's down to the fact that audiophiles want to look at cables in isolation, when in fact most of what they're hearing are changes in the amp, when it's called upon to perform differently. Why isn't the press writing about this?"

But he says it nicely.

Down the line
How does someone get started down the road toward skinny cables and plastic amps?

"My background is in mechanical engineering," says Morecroft, "but I've always had an interest in electronics and music. Years ago, I was using a Naim preamplifier and living in the country, way up in Scotland, at the end of the supply chain for electricity. I didn't think the preamp was performing as it should, and there were obvious problems with the power supply not keeping up with changes [in the delivered AC power]. So I had a closer look. Naim, at the time, was using 78-series IC voltage regulators—but then I found the LM317 regulator. I tried it and got very good results with it, and took it around for people to hear..."

That was the start, and by 1978 Denis Morecroft had made his first DNM product: an accessory power supply, soon followed by the first DNM preamp. It wasn't long before Morecroft had made a name for himself as an audio engineer to be reckoned with; years later, he was invited to join the NXT development team in Huntingdon, Cambridgeshire. But because his work has all been with semiconductors, I wondered if Morecroft had ever been attracted to tubes as amplifying devices—and, in particular, the single-ended triode movement, because so many of his ideas seem to have anticipated it, and because he has long championed low-power amps as superior.

"SETs? I was fascinated by that whole thing. There are good ones and bad ones, of course, and the good ones are superb. Good SETs, with no feedback, have a calming influence on the sound, especially in the highs. There's a 'busyness' to the highs of solid-state amps by comparison, superior though they may be in other ways."

Morecroft says that recent development work at DNM has been partly inspired by his observations of what SETs do well—and this has led him to take a fresh look at the way cables and, ultimately, other components interact with an amp or preamp. "In the context of an audio system, you have things connected to the center of the system through various ports," he explains, "and they will see those ports as reflectors at high frequencies. No matter how good you make your amp, you're still going to have trouble with all those ports.

"The correction, of course, is to terminate everything in order to match the impedances. You can do that with the cables, as some people have done, but it's better and more effective to do it at the thing which everything else must match to, which is the amp. The trick is to make the whole amp operate at a constant characteristic impedance." Morecroft's solution to this challenge—a dual-circuit approach suggestive of a differential pair—will debut later this year in a new version of DNM's preamplifier, the Series 3D, which will also incorporate new three-dimensional circuit-plotting techniques. (But as the successor to the DNM Series 3C, the new model name is, in Morecroft's words, "a fortunate coincidence.")

Uniquely—as far as I know—owners of older DNM preamps will have no trouble upgrading to the new one, because DNM is an avid recycler: Buyers of new DNM preamps and amps are guaranteed a certain dollar amount as a trade-in, should they ever decide to move up the ladder. This benefits audiophiles at the top of the food chain, and the krill as well: When older DNM units are traded in, the company tests, re-builds, upgrades, re-tests, and guarantees the units for sale at a lower price, offering them as components in their Start series. "The used-gear approach reflects our total dissatisfaction with how equipment is sold," Morecroft says. "Some poor fellow buys something very, very expensive, and then it goes out of fashion..." Recycling even applies to DNM's packaging: Preamps and amps are supplied in protective wooden crates, which are returned to the dealer after unpacking—and ultimately used again.

Up the hill
All right, then: You're a clever designer blessed with the ability to re-think accepted notions. You build your products well, with little regard for convention and no respect for techniques that don't result in good sound. You design parts that are so good your competitors buy them from you. Your ideas are ahead of their time. And you're nice to people: No one in the industry has a bad word to say about you. So you're bigger than Sony, right?

Denis Morecroft sighs amiably. "People really do believe they need these large cables and large amps, so we've got a lot of explaining to do. It's a continuous uphill struggle...

"Some people could say we are unnecessarily...complete," Morecroft adds with gentle irony—then pauses, before finishing with another sigh: "I'm prepared to accept that."

Coming next month: DNM's US distributor, Concert Sound of San Antonio, Texas, is loaning me a full set of DNM electronics and cables. I'll report on their sound in the May issue. Meanwhile, you can visit the Concert Sound website, or call them at (210) 229-1111. DNM's phone number in the UK is (44) 1480-457989.