Solid State Power Amp Reviews

Recently I found myself on the phone with Linn's chief design engineer, Bill Miller, talking about switch-mode power supplies. Affable Mr. Miller was ensconced in Linn HQ in Glasgow, Scotland. After a bit I inquired if Head Man Ivor Tiefenbrun was about the manse, and was quickly handed over. "You're such a cheeky guy. Why'd you call it the Klimax?"

"Well, Jonathan," Ivor breathed soothingly in a lilting Scots burr, "it simply represents the climax of many years of werrrk, you see..."

Yeah, right. I smiled and considered the veritable field day of bad jokes awaiting my twisted sense of humor.

In fact, the Klimax is perfectly named. It's billed as a "solo" single-speaker power amplifier designed for multichannel audio and audio/video systems. At the 1999 CES, This Jaded Reporter was stunned into silence—imagine—by a wall-mounted vertical array of eight Klimax monoblocks on an Linn Aktiv system fed by a suave Linn CD12 CD player. Gadzooks!

The look of the amp is pure Star Wars Contemporary from any angle. Incredibly, each amp is only about 14" square, no more than about 2½" tall in its stockinged feet, and weighs an easy-to-handle 20 lbs or so (footnote 1). Heave it aloft and regard the masterful work of Alistair Brown, Linn's head of industrial design. From the bottom-rear three-quarters view, it looks ready for the next space-epic fracas. The cooling fan—the afterburner—is caged in a stubby housing at the rear, and the underside is slotted and shaped like fellow Scot David Coultard's F1 McLaren Mercedes. The elegantly louvered top-plate overhangs the rear deck, so you'd best be prepared to mount 'em high or get way down low on your knees, knave. Ya gotta suffer for your art, they say.

The beautifully finished case is precision-milled from two solid sections of aluminum alloy by a computer-controlled multi-axis machine. The top plate is finished off with a Swiss SIP vertical jig borer. Sounds impressive. The dense case construction protects and stabilizes the electronics and functions as a "heat exchanger," as Linn puts it. Inside are two circuit boards, one each side of the central exchanger. One board comprises the power supply, the other the audio circuitry. This keeps the signal path simple and short, so as to generate minimal electrical noise.

In most amplifiers the power supply consists of a large transformer, a rectifier bridge, and "reservoir" capacitors often as big as the transformer. Many designs include voltage regulators to unkink and smooth the incoming cacophony of the AC mains. Regulators also bump up power dissipation, so efficient heat dissipation is a must. As Linn suggests, the bulk of these parts "dominate" the size and "tightness" of the signal path. Conventional power supplies are, however, simple, reliable, tolerant of overload, and predictable in behavior. Then again, Linn points a finger at them for being "heavy, slow to respond, inefficient, causing high mains-power distortion that can produce electrical and acoustic noise. They also require a relatively long and exposed audio path." They've got a point.

The Klimax runs on Silent Power® Brilliant® Switch Mode Power Supply technology, which Linn has been developing in their lower-powered products for several years. The concept isn't new; switch-mode supplies have been powering computers for ages. But their use in audio has been problematic. The potential benefits, according to Linn, are their diminutive size, efficiency, fast response, tolerance of mains input and loads, and "environmental friendliness." The downside includes complexity, electrical noise, unreliability, complex certification requirements, general design difficulties, and high engineering costs. (You know, Linn makes a good case against switch-mode themselves!)

In switch-mode power supply the incoming AC mains is filtered and rectified to generate an extremely high-voltage DC supply of 300 to 350V. That's too high for the circuitry to draw from, not to mention that it's connected directly to the incoming mains supply. (The manual cautions, by the by, that the case shouldn't be opened by anyone but a qualified Linnie.)

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Footnote 1: "About," "or so"...the manual quotes millimeters and kilograms.