Krell KRC-HR preamplifier & Audio Standard power amplifier Audio Standard power amplifier

Sidebar 4: The Krell Audio Standard power amplifier

The scene: Larry Archibald's last New Year's Eve party. Larry was mixing records and CDs into a set orchestrated to take his guests from smoldering tension to full-blown dancing frenzy just as the year changed. His living room is huge, and his speakers are the power-hungry Thiel CS-5is, powered on this occasion by the Krell Audio Standards. By 11:30, Marvin Gaye's "Sexual Healing" had packed the dance floor. JA and I stood atop the three stairs that lead down to the living room, watching while Larry tweaked the volume just a leetle louder, causing the dance floor to churn. John leaned over and murmured, "Sometimes seven watts per channel just won't cut it."

Indeed.

Another evening, six months later: JA had come to my place for a working dinner. While listening to the Aerial 10Ts driven by a Krell KSA-300S, John spotted the KASes and suggested we install them. I'm not sure what he was expecting, but I figured we'd tighten up the bass a bit and maybe get the sound to cohere a smidge better.

We sure weren't prepared for what we heard. Mouths agape, JA and I looked at one another. The bass was tighter and better integrated into the sound as a whole, but there was no aspect of reproduction that wasn't improved by several quanta. The sound inhabited the room naturally and absolutely. "If that," he said, pointing at the '300S, "is worth ten grand, then these amps really are worth $35,000! Someone has got to write about them."

Agreed. In fact, we should have acknowledged these remarkable products a long time ago.

The Audio Standard is a double-decker amplifier: its regulated power supply occupies a chassis separate from, and equal in size to, that holding the audio circuitry. The power supply has an LED readout (which can be turned off) that displays the voltage coming out of the wall. The audio portion of the amp—the top deck—features a large oval meter offering a variety of illumination and readout configurations. This gives the KAS a slightly retro, somewhat cyclopean, look.

Regulated supplies ensure a constant-voltage delivery to the signal stages, but they typically have one major disadvantage: they can't produce the instantaneous and short-duration power that dynamic peaks demand and get from amplifiers with sloppier supplies. Krell gets around this shortcoming by using its "Anticipator" circuit, which prompts the supply to increase voltage output for seven seconds, allowing the amp to bull its way through the peak. Krell claims that this circuit is triggered well in advance of the actual demand.

The Anticipator circuit also plays a role in the audio portion of the amplifier by controlling Krell's Sustained Plateau Bias system, which is designed to maintain class-A output bias while simultaneously keeping power consumption and heat dissipation to a minimum. It accomplishes this by utilizing five discrete bias levels, each equivalent to a class-A amplifier of proportionately increasing power. By monitoring the input signal, the SPB system determines the bias level required to maintain pure class-A operation of the output stages no matter what the load. The amp maintains the higher output level for 90 seconds before changing back to a lower level.

Does it work? I was never aware of the switching process, not even when putting Mahlerian demands on the output. I'm usually sensitive to the lag involved in all but the very best servo systems, but I just don't hear the Anticipator circuit at all. I haven't seen the utility bill yet, so I can't say whether or not Krell has succeeded in keeping power consumption down. But I've been using the KASes in a record-breakingly hot New Mexican summer, and they give off surprisingly little heat for such gargantuan class-A amplifiers.

One last point: the KASes only accept balanced input.

Let me state it as baldly as I can: Nothing in my experience of the High End prepared me for the Krell Audio Standard. It has the fullest body, the greatest coherence, the most effortless presentation, and the least presence of any audio product I've had in my system. People talk about sounds emerging from black backgrounds; the KAS's background is, quite simply, nonexistent, making your average black background seem more like the black velvet used for those Elvis paintings—all too present, and possessing a texture to boot.

When power is required, it's there; no big deal, you understand, it just happened to be in the neighborhood. Not that delicacy and nuance are slighted either—gossamer sounds and the slightest variations in dynamic shading are rendered with amazing grace. Could this duality of lissome power have anything to do with the Audio Standard's multiple amplifier personalities? Maybe so—I sure haven't ever heard an amplifier combine the traits of refined precision and brute power so well before.

Nor have I heard a big 'un keep better time. One reason Larry had all those people on the dance floor last New Year's is that the KASes boogie like the dickens.

Have I gone over the top? Maybe so. But these amps really are something. Yeah, they are big and expensive; otherwise, they don't have a downside. I, for one, could never afford them; heck, they cost more than my parents paid for their house. But having heard them, the realm of audio possibilities got a whole lot richer than even I had previously imagined. In a world of me-too products, Krell may well have set the audio standard.—Wes Phillips

Company Info
Krell
45 Connair Rd.
P.O. Box 533
Orange, CT 06477-0533
(203) 799-9954
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