Krell Evolution 400e Mono Power Amplifier


  • Brand: Krell
  • Product Code: 400e

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  • $11,995.00

The Evolution 400e amplifier is the smallest monaural amplifier in the Evolution Series. With a robust 400 watt output into 8 Ohms, this baby brother delivers plenty of punch. Potent enough for almost any application, the Evolution 400e shares the same sophisticated circuit topologies as its larger siblings but packs it into a smaller chassis. The Evolution 400e is perfect for when high performance is critical but space is at a premium.

Power Supply
The Evolution 400e is equipped with a massive with a 4,000 VA transformer. This power source is the backbone for the output of the Evolution 400e. With this foundation, the Evolution 400e delivers 400 watts into 8 Ohms, 800 watts into 4 Ohms, and 1,600 watts into 2 Ohms. The FTC mandates that power ratings are quoted using a 1000 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.

Circuitry Highlights
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 8 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 usable bandwidth of an Evolution 900 is 300 MHz; triple 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.

Frequency response
20 Hz to 20 kHz +0, -0.18 dB
<0.5 Hz to 125 kHz +0, -3 dB

Signal-to-noise ratio
>108 dB, wideband, unweighted, referred to full power output
>118 dB, "A"-weighted

25.4 dB

Total harmonic distortion
<0.02% at 1 kHz, at 400 W, 8 Ω
<0.15% at 20 kHz, at 400 W, 8 Ω

Input impedance
Single-ended: 100 kΩ
Balanced: 200 kΩ
CAST: 70 Ω

Input sensitivity
Single-ended or balanced: 3.04 V RMS
CAST: 3.04 mA RMS

Output power
400 W RMS at 8 Ω
800 W RMS at 4 Ω

Output voltage
160 V peak-to-peak
57 V RMS

Output current
37 A peak

Slew rate
100 V/μs


Output impedance
<0.055 Ω at 20 Hz
<0.064 Ω, 20 Hz to 20 kHz

Damping factor
>145 at 20 Hz, referred to 8 Ω
>125, 20 Hz to 20 kHz, referred to 8 Ω

Power consumption
Stand-by: 2 W
High Current Stand-by: 150 W
Idle: 210 W
Maximum: 2500 W

Heat output
Stand-by: 7 BTU/hr.
High Current Standby: 510 BTU/hr.
Idle: 720 BTU/hr.
Maximum: 3800 BTU/hr.

1 single-ended via RCA connector
1 balanced via XLR connector
1 CAST via 4-pin bayonet connector

1 pair Krell binding posts

14.50 in. W x 9.75 in. H x 20.65 in. D
368 mm W x 248 mm H x 525 mm D

120 lbs., 54.3 kg (shipping)
102 lbs., 46.2 kg (unit only)