Solid State Power Amp Reviews

Once upon a time, in the early days of class-D amplification, the very notion that the ELAC (ELectroACoustic) Alchemy DPA-2 Stereo/Mono Power Amplifier ($1495 each) uses a class-D output stage would cause some readers to turn the page (footnote 1). But as class-D amplifiers established their pedigree as bona fide hi-fi components, audiophiles have begun to embrace the notion of a lightweight, cool-running amplifier that will not dramatically increase the electric bill and that, when properly executed, can be quite musical.

Others, though, may still balk at the suggestion that this skinny, 14lb, class-D device from the Americas division of ELAC Germany—auditioned here in bridged monoblock configuration—can get listeners close to the heart of the music. Perhaps learning that the DPA-2 was designed by Peter Madnick, who also oversaw the design team for Constellation Audio and voiced all of their products, will encourage them to explore farther.

Peter Madnick on the DPA-2
When he developed the DPA-2, which combines a Hypex UCD class-D output module with a class-A input/driver stage, Madnick worked with ELAC's power supply designer to prepare the switching power supply that supplies the juice to its class-D module. Drawing on his experience designing close to 400 products, including 20 or 30 amplifiers for several companies, he and his team designed everything except the housing; cosmetics were left to a different ELAC team.

"We didn't spend much money on design aesthetics," Madnick acknowledged during an iPhone chat. "It's not beautifully milled jewelry." Even inside, "these amps are utterly simple. I don't want to make them into more than they really are. There is nothing similar between this product and Constellation.

"My goals were broad market appeal and bang for the buck. I've always been really good at value engineering—deciding where to spend the money and where not to spend the money....We wanted to make it lightweight, easy to carry around and install, and capable of running without putting out a lot of heat or consuming a lot of power when on. I wanted as high a performance as I could squeeze into a one-unit-high chassis, which is the standard 1¾" vertical space between the holes on a pro rack."

Sonically, Madnick's bottom line was that the DPA-2 had to sound like live music. His inspiration came from four decades of regular attendance at symphonic performances, often with season tickets, which currently place him seven rows back in the center section, where the combination of direct and reflected sound has maximum impact.

"I wanted to provide the kind of real-life transparency and clarity that you would not expect at this price point as well as an overall balance that would lead you to say, 'Wow, that thing's really good for the money.' My goals included dynamics, clarity, and the opposite of the bad reputation for harshness that class-D has had (even though we all know that there are great-sounding class-D amplifiers). I played with all sorts of class-D designs when they were first coming out, and they all sounded 'digital.' To me, that means harsh, unmusical, irritating, not contiguous and stitched together from lows to highs. That's also what early D/A converters sounded like, and some still sound like. It was a sound I couldn't have. Until we could find modules and techniques that would ensure that they wouldn't sound that way, I wasn't going to introduce a class-D amplifier."

Madnick had numerous amplifiers on hand—his own designs—to use for comparison. He also checked with ELAC speaker designer Andrew Jones to make sure that he was happy with the sound. Madnick listened with several loudspeakers from different brands and asked his speaker design "buddies" to evaluate his prototypes to make sure they would work with their models.

The DPA-2's input stage is a fully discrete JFET design that accepts both single-ended and balanced inputs. It also converts single-ended to balanced so that it drives the class-D modules with a balanced signal. The amp is completely DC-coupled: no capacitors in the signal path. The potential for DC offset is eliminated through the use of servo technology. Madnick says that the input stage produces a very clean, low-distortion, balanced signal that drives the Hypex modules without the use of feedback. He also noted that the DPA-2s don't get particularly hot—nowhere near hot enough to warm your hands after shoveling snow—and are approximately 93% efficient when you play them loud. "The louder you play them, the more efficient they get," he said. "400W out the output jacks means that you're consuming approximately 430W."

The DPA-2 can function as either a stereo amp or a monoblock; Madnick says you can't damage it if you accidentally switch it to mono while you're playing in stereo. The DPA-2 is bridged in mono: the left channel produces the positive phase of the signal and the right channel produces the negative phase. Madnick says that the DPA-2 could run into "any" impedance and should work fine with my reference Wilson Audio Alexia 2s.

A few of Madnick's choices aroused my curiosity. After he referred to the amp as a "hybrid," I asked why. Because it mates "a traditional JFET analog input stage, run from a linear power supply, with a class-D, PWM-type output stage that uses a switching power supply," he responded. "I erred early on by titling the amp with the initials DPA [for digital power amplifier], because these amps are not digital. Class-D is a PWM [pulse width modulation] technology which is really more analog than digital (footnote 2). But I carried on with the mistake in order to maintain consistency between the DPA-2 and its predecessor, the Alchemy DPA-1."

Why, given the linear power supply Madnick had used for the DPA-2's sensitive input stage circuitry, did he choose a noisier, switching supply for the class-D modules? "My experimentation over the years led me to discover that switching power supplies on class-D modules are fine. Noise isn't an issue with them."

Why did he use an older class-D module? "I've listened to the newer Hypex NCore modules....Frankly, I don't care that they measure better; they have to sound better, and to me they do not. I know that for a big part of the world class-D–module market, specifications are a really, really important, critical criteria. But we all know that things can measure great and not sound good and vice versa."

I've known Madnick for a good decade and a half and took the liberty to ask if, in retrospect, there was anything about the design that he might have done differently. "If I could have done it again, it might have cost more money, but it could have produced up to 700Wpc in mono," he acknowledged. "The specs might have been more impressive, but specs are not what I'm selling."

Outside, inside, and on the rack
Hallelujah: The DPA-2 comes with a manual—two actually, one in each monoblock box. The manual is also posted online. In my recent experience, newer and more expensive components are less likely to have a manual.

Setup was a cinch for 14lb amps that, if they had dog-friendly handles, one of our 21lb terriers could have easily dragged across the floor. In fact, dogs, babies, and even adults could easily knock the amps off their shelf or equipment supports if they're not careful (footnote 3).

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Footnote 1: In the comments that followed my first review for Stereophile, of the Dynaudio Focus 200 XD active loudspeaker, "georgehifi" declared, "there are many amongst us that give class-D a wide berth."

Footnote 2: Read Bruno Putzeys's take on this issue here.

Footnote 3: I've used stiff, heavy power cords that could probably pull a 14lb amplifier off the shelf or at least wrench it off kilter. But then not many DPA-2 buyers are likely to use power cords that cost many multiples of what the amplifier costs, as Jason does.—Editor