High-End Audio Equipment
Krell Industries, founded in 1980, is the premier manufacturer of high-end audio equipment, featuring award winning amplifiers, preamplifiers, CD & DVD players, surround sound processors, digital-to-analog converters, and loudspeakers for music lovers and home theater aficionados.
"It is hands down the best amplifier I've ever heard and the new benchmark for which all future cost no-object amplifiers will be judged."
Andrew Robinson - Home Theater Review
For over three decades, Krell has earned a distinguished reputation for engineering innovation and product excellence. The company's history is replete with product introductions that have deeply impacted the high-end audio industry. The most discriminating audiophiles and product reviewers have consistently recognized Krell components for standard-setting performance. The sheer breadth of Krell amplifiers' dynamic range capabilities conveys a startling realism that transcends previous designs. Seemingly unlimited frequency response, combined with unerring accuracy and fortitude, extend a tradition that began with the first Krell amplifier; the KSA-100. The KSA-100 was the first high power, high-current, true Class A biased stereo power amplifier available to audiophiles. It was the first Krell product, and its resounding success established Krell as an important new technological contributor to high-end audio.
From the KSA-100 to the present, Krell continually "pushes the envelope" of performance in our search for greater amplifier power. Exploration of new technologies, driven by a never-ending quest to elevate the standard of excellence, has resulted in breakthrough audio designs. Over the years, the Krell line of power amplifiers, including benchmark products such as the KRS-100, KRS-200, and the Audio Standard models, has established a legacy of unparalleled sonic performance.
The Krell product line has diversified, but Krell's fundamental research into amplifier design and performance remains at the core of the company's achievements. Every Krell component upholds the legacy, incorporating unique technologies that are the direct result of Krell's discoveries in audio amplification. They provide unprecedented linearity with the control and accuracy that only comes from superior current capability. The sound is lively and unconstrained, in a manner that evokes live performance and the true sound of instruments. The Krell legacy will continue to evolve with products that deliver innovative engineering, perfection in build quality, and outstanding audio performance.
NEW - KSA-i400 Power Amplifier - Owner’s Reference (pdf file)
The KSA-i400 is a state-of-the-art 400 watt/channel stereo amplifier. It incorporates Krell’s most advanced circuit topologies and Krell’s proprietary technologies iBias, XD, and Sym-Max. This gives the KSA-i400 an organic, spacious, and detailed presentation along with the rock-solid bottom end and effortlessness that Krell is known for.
iBias
iBias enables the KSA-i400 to operate in Class A up to its full rated power of 400 watts with absolute accuracy but without the heat produced by a traditional Class A design. It does this by using a novel circuit to unobtrusively monitor the current flowing through the output stage which is part of a closed-loop controller that makes sure this current never drops below a preset level (Class A means that it never drops to zero). This is what makes the amp both efficient and accurate.
The efficiency comes from the controller adjusting the bias to maintain that low preset current level as the signal and speaker load changes. Traditional Class A amplifiers set it for the maximum level all the time so they’re always dissipating the maximum amount of heat. iBias is like having a variable size Class A amplifier. If, for example, the signal and speaker are only requiring 10 watts, it’s like having a 10 watt Class A amplifier, all the way up to 400 watts in the case of the KSA-i400.
The accuracy also comes from maintaining that low preset current level. It doesn’t matter what the signal is doing or how the speaker impedance changes with frequency, by maintaining that preset current level the amplifier is always operating in Class A. Other variable bias schemes monitor the input or output signal to adjust the bias but that doesn’t take into account varying speaker impedance. This means they will sometimes apply more bias current than necessary or drop out of Class A operation.
XD
XD is a technique for lowering the amplifier’s output impedance. This results in better control over the speaker drivers which improves musical dynamics, depth, and dimensionality. It is very dependent on maintaining thermal equilibrium in the output stage so that all the output transistors are contributing equally to the signal output. The KSA-i400 uses a massive aluminum device bar to mount the output transistors and also employs special temperature compensation across the device bar to limit temperature variations. With its low output impedance, the KSA-i400 achieves a damping factor of better than 800.
Sym-Max
Sym-Max is short for “Symmetry Maximization.” The circuitry in the KSA-i400 is differential, meaning that there is a positive half and a negative half. The transistors in this circuitry are complimentary, meaning opposite polarity but with equal characteristics. In practice they are not so equal which means the circuit is operating asymmetrically. Sym-Max makes small adjustments in the circuit parameters to remove this asymmetry. The result is that 2nd order harmonic distortion is almost completely eliminated. This dramatically opens up the sound stage with more detail and a better sense of pacing, making for a more realistic experience.
Power
The heart of any power amplifier is the power supply. The KSA-i400 has a massive power supply consisting of 5400VA of transformers and 188,000uF of filter capacitance. Delivering this power to the output circuit is a combination of gold-plated circuit boards and silver-plated sold copper buss bars with a very short physical path for extremely low impedance. This, along with the audio circuitry enables the KSA-i400 to double its power from 400 watts into 8 ohms to 800 watts into 4 ohms and even 1600 watts into 2 ohms. It can drive 1 ohm speakers and will deliver a peak current of up to 62 amps.
Circuitry
The KSA-i400 uses Krell Current-Mode circuitry with advanced current mirroring that is balanced, differential, and direct-coupled. Each stage is independently tuned and matched to the previous stage for optimal operation. The output stage consists of 16 pairs of high-power audio transistors and 8 pairs of audio driver transistors. This results in a frequency response greater than 100kHz that is flat at 20Hz for effortless reproduction of the audio band.
Control and Protection
The KSA-i400 is microprocessor controlled and has Ethernet connectivity and a 12VDC trigger input for easy connection to a home controller. The Ethernet connection allows access to the KSA-i400 web page for status information and control. The KSA-i400 is protected against high DC on the outputs, output short circuit conditions, and power brown outs. The protection operation is conveniently indicated on the front panel status lights and the web page.
