Krell KMA-i800 monoblock energy amplifier

Ever since I raved about Krell’s Ok-300i built-in amplifier after it was launched in early 2019, I’ve needed to assessment different Krell merchandise. After spending greater than a yr and a half (since its prerelease announcement) awaiting the chance to assessment Krell’s new flagship mono energy amplifier, the KMA-i800 ($73,000/pair), the time has come. Both Krell fashions make the most of the corporate’s proprietary iBias expertise, albeit in numerous iterations, and each have been designed by longtime Krell engineer Dave Goodman (footnote 1).

In the conclusion to my Ok-300i assessment, I wrote, "The Krell … has the smoothest, most listenable, and most all-of-one-piece sonics of [any] built-in I’ve reviewed. … There’s a spherical edge to its photographs that some may equate with the gentlest sprinkling of heat, however others would describe as listener pleasant. It actually leaves me smiling." I believed it so glorious, and such a superb purchase for a Roon-ready streaming built-in with an non-obligatory onboard PCM/DSD/ MQA DAC, that I urged a buddy to purchase one. More than three years later, he is nonetheless smiling.

Would Krell’s new, way more highly effective class-A monoblocks encourage the identical pleasure? As a lot as asking the query might sound like the primary installment in a made-for-TV cleaning soap sequence, discovering out made all of the work I did carting these beasts round greater than value it.

Design and engineering
The product overview for the KMA-i800 monoblock amplifier on the Krell web site (footnote 2) lists the next key applied sciences: differential output; iBiassee beneathpaired with XD expertise, which lowers output impedance (footnote 3); Sym-Max (Symmetry Maximization), mentioned to nearly remove second-order distortion; an influence provide "consisting of 5400VA of transformers and 188,000µF of filter capacitance"; energy supply by way of gold-plated circuit boards and silver-plated solid-copper busbars "with a really brief bodily path for terribly low impedance"; "Current-Mode circuitry with superior present mirroring that’s balanced, differential, and direct-coupled," with every stage individually tuned; an output stage with "16 pairs of 200W audio energy transistors and eight pairs of audio driver transistors," leading to a large bandwidth; safety in opposition to extra direct present and brief circuits on the outputs, plus voltage sags ("brown outs"); and Ethernet connectivity that enables standing monitoring and management by way of a webpage.

I mentioned iBias in depth within the sidebar to my Ok-300i assessment. Krell’s product overview provides a KMA-i800particular rationalization, fleshed out on its iBias expertise web page. In brief, "iBias permits the [monoblock] to function in class-A as much as its full rated energy of 800 watts with absolute accuracy however with out the warmth produced by a conventional class-A design. It [uses] a novel circuit to unobtrusively monitor the present flowing by the output stage. This is a part of a closed-loop controller that … [adjusts] the bias to take care of [a ] low preset present stage because the sign and speaker load modifications [regardless of ] what the sign is doing or how the speaker impedance modifications with frequency. … By sustaining that preset present stage the amplifier is all the time working in class-A."

In a latest telephone chat with Goodman and Krell proprietor Rondi D’Agostino, Goodman mentioned that Krell’s present designs are principally the end result of an evolutionary course of that improves upon his work and the work of different engineers. "On the opposite hand, iBias is revolutionary. It got here out of the thoughts of one in all our earlier engineers, however he wasn’t round lengthy sufficient to place it right into a manufacturing mannequin amplifier. That was my job."

Dave mentioned that implementation of iBias within the KMA-i800 monoblock contains new circuitry "that provides feed ahead compensation to make it reply slightly bit sooner and extra precisely to the amplifier’s biasing wants." He additionally famous that iBias is what permits the monoblock to ship 800W of class-An influence whatever the load (footnote 4).

"That’s the actual fantastic thing about iBias," he declared in his customary low-key method. "It does not rely on the speaker load, it does not rely on the way it varies with frequency, it does not rely on what the enter is doing. You have a hard and fast quantity of class-An influence to work with, and also you get that it doesn’t matter what. The class-A operation you get nearly on a regular basis gives you that good, heat, easy-to-listen-to sound you affiliate with class-A amplifiers."

I requested Dave what different features of the KMA-i800’s expertise he thought-about most original and necessary. He replied, "XD expertise lowers the output impedance considerably and ends in much more management over the speaker drivers. This reduces the acoustic distortion you’d in any other case get when the drivers are much less managed and flapping round a bit on their very own exterior of what the sign desires them to be doing. It produces much more front-to-back depth to the soundstage and much more black area across the performers and devices.

"Sym-Max expertise considerably reduces second-order harmonic distortion and brings out extra element. It actually accentuates your notion of the pacing. You get a way more well-defined sense of timing and deliberateness from the musicians on the recording. It’s additionally simpler to separate the performers on the soundstage. Together, XD and Sym-Max ship a way more detailed, life like, and enveloping sound expertise.

"Sym-Max expertise is utilized all through the amplifier to scale back second-order harmonic distortion at each stage. By the time you get to the output, that distortion is sort of imperceptible.

"The second and third harmonics are the dominant harmonics within the distortion content material of most amplifiers. In tube amplifiers, the second order is the dominant harmonic. They’ll let you know that distortion sounds good. But what’s actually occurring in tube amplifiers is the third harmonic, which is primarily liable for harsh, fatiguing sound, is way decrease than the second harmonic. That’s why tube amplifiers with much less third-order harmonic distortion are inclined to sound considerably candy and nice. But the second remains to be excessive sufficient to finish up masking plenty of the efficiency’s element and spaciousness. With the Sym-Max and a number of other different design strategies, we actually decrease each second- and third-order harmonic distortion and ship the very best of each worlds. The third remains to be fairly low within the KMA-i800 resulting from a number of the superior current-mode strategies we make the most of.

"One of the opposite key design options, in comparison with earlier designs, is the addition of additional driver transistors within the output stage; this offers significantly better management and pace over the output gadgets they’re linked to. It additionally contributes fairly a bit to the general efficiency of the amplifier. The configuration grew out of growing a purpose-built amplifier for the tweeter part of the Apogee Grand speaker system."

Goals and values
Given the KMA-i800’s big energy outputKrell says it might probably output 800W RMS into 8 ohms, doubling twice to 1600W into 4 ohms and 3200W into 2 ohms, and may drive audio system of 1 ohm impedanceI questioned whom Dave and Rondi envisioned as patrons. "There are loads of individuals on the market who’ve relatively massive rooms and wish commensurately massive audio system they will play loudly," Dave replied. "No one goes to make use of this a lot energy, nevertheless it makes common listening ranges, which can go as much as 100W, sound significantly better as a result of that is a small share of the overall attainable energy output. It’s extra linear than an amp that tops out at 100W, as a result of as you strategy the restrict, your distortion goes up dramatically. A high-power amp provides you rather more high quality than an amp whose energy precisely meets your wants." As somebody conscious about the arbitrary and continuously over-exaggerated divide between the 2 viewpoints generally labeled "subjectivist" and "objectivist," I requested Dave, "When you developed the KMA-i800, have been you measurements or at sound? What was the ultimate arbiter that led you to declare, ‘It’s performed!’?"

"Quantitative measurementsdistortion and noiseare there to let you already know you are heading in the right direction," he mentioned. "Certainly, if the distortion is excessive sufficient, you are going to discover it straight away; beneath a sure stage, you will not discover it. Some of the circuit-design strategies come into play if you resolve easy methods to decrease that distortion. Once you get the design to function inside an affordable vary of the target specs, then you definitely begin your listening evaluations and make changes based mostly on the way it sounds."

Footnote 1: Goodman, who has been with Krell since 1987, designed Krell’s Altair, KAS and KAS-2, KSA-200S and KSA-300S, KAV-500, and KAV-250A amplifiers. He additionally designed a number of the circuitry within the FPB amplifiers.

Footnote 2: See krellhifi.com/kma-i800-mono-amplifier-product-overview.

Footnote 3: See krellhifi.com/ibias-technology.

Footnote 4: With a typical class-A amplifier, the facility working with class-A bias is halved when the load impedance is halved.

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March 1, 2024 at 05:10PM