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It's hard to overstate the importance of Krell Industries in the history of high-end audio. Founded in 1980, Krell was the audio equivalent of Lamborghini—an audacious riposte to more Ferrari-like rivals such as Mark Levinson and Audio Research. For almost four decades, Krell has gone on from strength to strength, introducing a stream of ever more ambitious products that tested the depth of their customers' pockets, along with the strength of their audio equipment shelving. With their new iBias class-A design and new products, Krell has reestablish its brand once again as a world leader in the high-end audio market.

Krell amplifiers have always been overstated in design and understated in their on-paper specifications. Back in the 1980s, we would talk about “Krell watts,” where the amp's massive power supply and conservative on-paper power rating meant that it could drive speakers in real world systems way beyond what the numbers would suggest.

KRELL'S NEW XD SERIES WITH ENHANCED CLASS-A, iBIAS TECHNOLOGY:
Krell's history is rich with breakthrough Class A amplifiers that have helped build the Krell legacy of offering the best sounding amplifiers available. Audiophiles have always considered Class A technology to be the best sounding operating state for amplifiers. However, despite Class A's unrivaled sound quality, it has fallen out of fashion because of recent demands to reduce power consumption and heat in home electronics products. Krell engineering took this challenge and redefined the meaning of high performance power amplifier. Our goal - unmatched performance, elegant design, and a compelling array of features. The breakthrough - a patent pending circuit delivering Class A operation without the excessive heat and wasted energy of conventional designs, housed in a striking new form factor, with network connectivity for advanced access and monitoring. The sound is open and unconstrained, in a manner that rivals live performance and the true sound of voices and instruments. Music and dialogue are reproduced with a richness, detail, and startling dynamics that fill a room.

Plainly stated, Class A designs are the most musically accurate circuit topology available. Class A amplifiers do not suffer from the inherent distortions that all Class AB amplifiers experience. In a traditional Class A design, the output transistors conduct full current at all times regardless of the actual demand from the speakers. Often, only a fraction of this power is needed to reproduce an audio signal at normal listening levels. The rest of the power is dissipated through the amplifier’s heat sinks, producing large amounts of wasted heat. With Krell's iBias™ technology, bias is dynamically adjusted, so the output transistors receive exactly as much power - but only as much power - as they need.

Krell's iBias Class A technology allows our latest amplifiers to run in full Class A mode to full power while minimizing heat generation. Previous efforts at using a "tracking" bias, while effective, only measured the incoming signal and set bias levels from this information. Our new patent pending iBias technology significantly elevates the effectiveness of previous designs by calculating bias from the output stage. This seemingly small change in topology results in a dramatic improvement in sound quality, especially midrange richness and purity.

The core of the technology is an innovative, patent pending design for a dynamic intelligent bias circuit. Our iBias Class A circuit directly measures the output current of the amplifier and adjusts the bias to the optimum level. Because iBias Class A measures the output current, the real time demands of the specific speaker connected to the amp are directly incorporated into the circuit function. In addition, iBias Class A even reduces the bias when the signal is at very low levels, making its operation undetectable by ear and even by standard amplifier measurements. In others typical sliding bias schemes, the circuit merely estimates how much bias is needed based on the input signal and an "assumed speaker load." Compared with iBias Class A, these sliding bias technologies are much less effective - and much less accurate.

XD UPDATE
Development of their "XD' circuit, is now incorporated in all new power amplifiers leaving the factory, according to David Goodman of Krell, “The XD' update to the Chorus/ Duo/Solo amplifiers reduces the output impedance to less than half of its original value. This lower output impedance better damps unwanted speaker vibrational modes. Changing the output impedance also necessitated re-compensating each amplifier stage to achieve optimal critically damped transient response. This ensures that the amplifier accurately follows the dynamics of the input signal."

BETTER SOUND
Building on the unique Active Cascode Topology foundation of the NEW Rrange of amplifiers feature more precisely balanced current sharing among the seven sets of Active Cascode Quartets that make up the output stage. This greater precision elevates an already impressive performance envelope and provides greater amplifier reliability. Audible at all volume levels, this improvement is independent of load current. Although negative feedback in the Evolution amplifiers was already extremely low, a mere 14 dB---several orders of magnitude lower than other manufacturers' power amplifiers, modifications to the feedback circuitry allow for more ideal operation completely independent of the signal level. The results are greatly enhanced inner detail and micro-dynamics with smoother high frequency response.

LESS HEAT, LOWER ENERGY CONSUMPTION with KRELL'S unique iBias technology