Solid State Power Amp Reviews

Classé Audio's DR-3 once again brings to the fore the issues of class-A vs class-AB, weighty vs small and efficient, and brute-force expensive vs clever and inexpensive.

A well-worn, if unproven, audiophile rule of thumb says that a small, quick amplifier will sound better than a very powerful one (footnote 1). Among low-powered amps, those that operate in "pure" class-A are thought to be sonically superior. Pure class-A means the amplifier must run a constant high bias (more than one ampere), so the output devices never turn off (footnote 2). This high bias current means the amplifier emits a lot of heat; to avoid noisy fans, extensive, expensive metal radiating fins are needed to disperse the heat.

Past class-A designers have suggested it as an intrinsically superior operating mode because it reduces several types of distortion. But far more designers have worked in class-A/B, resulting in great refinement and almost complete elimination of the non-linearities class-A is said to uniquely address.

Other class-A designs have taken different directions. Nelson Pass's innovations with "sliding class-A", where the bias level adjusted to meet signal level, increased the amplifier's efficiency and lowered its heat dissipation. It was not, however, regarded as pure class-A by a number of audiophiles, and is not Threshold's current claim to fame. "Sliding class-A" was, however, stolen by several Japanese firms for use in their mid-fi gear.

Rolls-Royce packaging of a massive but low-powered amplifier with a high price tag had its roots in the Mark Levinson ML-2, a high-end product of the 1970s just now coming up fo replacement by MLAS. The ML-2 itself attracted criticism as an audiophile "excess," but this didn't seem to affect its commercial success; Levinson sold hundreds of them.

The ML-2, once labelled the "Gold standard" of amplifiers by The Audio Critic's Peter Aczel, became the most prominent example of pure class-A design. Now available at $8848/pair on custom order only, it came on a mono chassis weighing 65 pounds, with large heat radiators lining both sides and resembling an elaborate bent metal sculpture—a modern artist's concept of technology gone wild. Each ML-2 was fully regulated, ran a steady 4.5 amperes of bias current, and pumped 300 watts of heat into the room at idle.

The ML-2 was preferred by high-end dealers for driving complex speaker systems such as electrostatics, especially the Mark Levinson HQD hybrid speakers (footnote 3). During a subjective listening test run in my listening room several years ago, the ML-2s won out sonically over Bedini, Hafler, and Audire amplifiers while driving a pair of Quad electrostatics. The ML-2 produced a faster, more transparent and sweeter sound, with much more information than the other amplifiers.

This "heroic" design philosophy, extreme in its disregard for efficiency, size, and weight, inevitably results in large, costly amplifiers. The DR-3's 70lb chassis, prominent heatsinks, $2895 price, and low power output put it squarely in the class-A tradition. Although the DR-3 resembles the ML-2's massive metalwork, it is unlike the ML-2 because it is a stereo amplifier, costs far less, and does not use Levinson's Camac connectors which, requiring adaptors or unique cables, themselves involve the expenditure of extra hundreds.

Class-A has become little more than a marketing buzzword in recent years, but Classé Audio's interpretation of it in the DR-3 is far more rigorous than the Japanese receivers with front panel pushbuttons that drop the power rating and step up bias current to deliver "class-A." The manufacturer's name, after all, is a double pun across two languages: the French Classé sounds like "Class-A" and reads like "classy".

The DR-3's price point and power rating, which yield an extraordinarily expensive $58/watt, cause one to worry about expending money instead of good sense. And the sufficiency of a mere 25 watts may concern audio buffs who own inefficient speaker systems.

Design Details
Suspicions of expensive watts aside, what really matters are the DR-3's sonics, and here the news is very good. This exotic, low-powered but big-sounding amplifier proved itself over and over in my listening tests. Its modest power rating fails to describe its dynamics, speed, transparency, sweetness, and ability to communicate instrumental resonances.

It is this quality of detailing and sonic sweetness that Classé Audio's designer, David Reich, aspires to. Reich believes that the class-A operating mode avoids sonic irritants, including crossover notch distortion, and slew-induced distortion. He claims that the DR-3 displays smoother and more evenly distributed harmonic spectra during clipping. This performance is also related to the DR-3's quality of construction, which is first-rate: polyfilm capacitors for coupling and bypassing key circuit areas, shield plates to reduce hum in input circuitry, very heavy-gauge OFC (oxygen free copper) internal wiring, floating-ground power supplies, and dual-mono construction.

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Footnote 1: I have found a number of very high-power amplifiers with excellent sound, such as the Onkyo M510.

Footnote 2 Output devices (in this case transistors) typically amplify only half the audio signal; they are paired to complementary devices that "take over" the signal as it crosses the zero-voltage axis. Maximum efficiency, known as Class-B operation, dictates that the device should turn off (stop conducting) as soon as it stops processing the signal, but this produces a horribly harsh form of distortion labeled "crossover notch" distortion. The other extreme is to bias the transistor at such a high amperage that it never turns off, even with no signal present; this is class-A. Class-AB is a compromise: up to reasonable outputs (say, 20 watts) the biasing is sufficient to maintain class-A operation; at higher outputs, the amp reverts to class-B, but the high output is said to swamp the resulting distortion, and clever circuit design can keep most of it from happening in the first place.—Larry Archibald

Footnote 3: HQD stands for Hartley/Quad/Decca, the names of the drivers used. The system could cost upwards of $55,000 if you included six ML-2s, Levinson cable throughout, and the "basic" speaker, which cost $24,000/pair. J. Gordon Holt attracted mighty wrath (and you thought CD was the first time everyone came down on him!) by listening to a carefully set-up HQD for two minutes and condemning it out of hand. Wrath or not, his criticisms were well-founded.—Larry Archibald