Krell Evolution 900e Mono Amplifiers

Mint condition set of Krell Evolution 900e mono amplifiers in black. I am selling this pair of amps for a customer who received them brand new from the Krell factory in August 2013. They are simply stunning to behold and have what seems like unlimited power. These have to be some of the finest amplifiers available. These will be shipped via freight on a Krell factory pallet and in their original factory boxes.

From Krell;

Evolution 900e

Mono Amplifier

The Evolution 900e is the most powerful member of the Evolution Series. At a staggering 3,600 watts into a 2 Ohm load, the Evolution 900e is a virtually limitless source of power for any speaker. This power capability is coupled to a new green operating mode that reduces standby electrical draw to a mere 2 Watts. While power is essential for lifelike volume levels and realistic dynamics, the true benefit of this engine is its ability to dominate a speaker and extract the ultimate performance from any speaker design. Dedicating one amplifier per speaker is the recognized best path to ultimate performance. As such, the Evolution 900e is a monaural design requiring two for stereo reproduction or left and right power amplifiers in a home theater system.

The Evolution 900e is equipped with two 3,000 VA transformers and 108,000 μF. This power source is the backbone for the output of the Evolution 900e. With this foundation, the Evolution 900e delivers 900 watts into 8 Ohms, 1,800 watts into 4 Ohms, and 3,600 watts into 2 Ohms. The FTC mandates that power ratings are quoted using a 1,000 Hz sine wave into a fixed 8 Ohm resistor with final power specification stated at 1% distortion. Krell engineering considers this specification too lenient and not indicative of what an amplifier is required to provide. Krell designs to a much stricter standard. Our power tests use a 20-20,000Hz signal into 8, 4, and 2 Ohm loads with our final specifications stated for .1% distortion.

Internal high-current line conditioning circuitry effectively blocks RF noise entering via the AC line and compensates for any asymmetry or DC offset in the power waveforms. The amplifiers' low level and gain stages are powered via multi regulated rails that provide total immunity from supply fluctuations and assure noise-free circuit operation. Primary rail voltages are quasi-regulated, enabling an "on-demand" supply of power that is highly responsive to dynamic load.

Krell's new Active Cascode Topology™ is a significant departure from traditional amplifier circuits where the positive and negative rail voltages are each applied entirely across a single row of transistors. High voltage swing and gain requirements dictate that the transistors be "pushed" into non-linear operating regions and, in some cases, dangerously close to breakdown. Krell topology divides the full voltage swing across multiple rows of transistors, and all devices are active-biased (i.e., they all carry the audio signal). Because individual transistors in the cascode array "see" only a proportional fraction of the rail voltage, they operate in a region that provides optimum linearity, gain, and safety. And because the devices are not being pushed to their limits, the amplifier runs cooler and more reliably. The improved linearity and stability greatly reduces the need for negative feedback, which is known to cause sonic degradation. Krell Evolution power Amplifiers use only 14 dB of feedback throughout the topology-a small fraction of the amount implemented in typical designs.

Krell Active Cascode Topology offers several performance advantages. It breaks through bandwidth limitations of conventional designs and delivers very high current. The power bandwidth of an Evolution 900e is 120 kHz; far greater than the bandwidth of a typical high performance amplifier. The result is near perfect performance in the audible range with no phase anomalies typical of lower bandwidth designs. Because the "work" is spread across multiple devices, the amplifier is more load tolerant. Open-loop output impedance is extremely low-about one hundred times lower than with most power amplifiers-ensuring exceptional speaker control. All of these performance gains are achieved while maintaining a high rail voltage, which provides a beneficial "flywheel" effect-a de facto regulation that enables the amplifier to better deal with sudden changes in power requirement, such as those caused by large signal transients.

Evolution amplifiers feature Krell CAST technology.  CAST is a unique circuit and connection breakthrough that eliminates distortions inherent in voltage based amplification. A complete Evolution (source, preamplifier, and amplifier) system, connected with CAST interconnects reduces the number of voltage gain stages to the minimum, one. The resulting noise floor is approaching the theoretical limit of technology. Emanating from a completely black background, music explodes from absolute silence moving the listener closer to the goal of recreating the live musical event in the listening room.

Specifications;

Frequency Response

20 Hz to 20 kHz +0, -0.18 dB

<0.5 Hz to 120 kHz +0, -3 dB

Signal to Noise Ratio

>113 dB, unweighted, referred to full power output

>122 dB, "A"-weighted

Gain

25.4 dB

Total Harmonic Distortion

<0.02% at 1 kHz, at 900 W, 8 Ohms

<0.15% at 20 kHz, at 900 W, 8 Ohms

Input Impedance

Single Ended: 100 kOhms

Balanced: 200 kOhms

CAST: 70 Ohms

Input Sensitivity

Single Ended or Balanced: 4.55 V rms

CAST: 4.55 mA rms

Output Power

900 W RMS at 8 Ohms

1800 W RMS at 4 Ohms

Output Voltage

240 V peak-to-peak

85 V RMS

Output Current

60 A peak

Slew Rate

90 V/µs

Output Impedance

<0.023 Ohms, 20 Hz to 20 kHz

Damping Factor (referred to 8 ohms)

>350, 20 Hz to 20 kHz

Transformer

Two 3000 VA (6000 VA total) for audio circuitry

One 10 VA for digital control circuitry

Power Supply Capacitance

108,000 µF

Power Consumption

Standby: 2 W

(High-current standby: 440W) Idle: 650 W

Maximum: 5000 W

Heat Output

Stand-by: 7 BTU/hr. (High-current standby: 1500 BTU/hr.

Idle: 2200 BTU/hr.

Maximum: 7700 BTU/hr.

Inputs

1 single-ended via RCA connector

1 balanced via XLR connector

1 CAST via 4-pin bayonet connector

Outputs

1 pairs Krell binding posts

Dimensions

17.3 in. W x 9.8 in. H x 26.1 in. D

438 mm W x 248 mm H x 662 mm D

Weight

Shipped: 190 lb., 86 kg

Unit Only: 175 lb., 79.2 kg