The Evolution 403e is the most powerful three channel amplifier available today. Housed in the same chassis as the Evolution 900e, the Evolution 403e is the perfect choice for Left, Center, and Right channel amplification in a high performance home theater. For reference caliber performance, coupling the Evolution 403e to Evolution 900e, Evolution 600e, or an Evolution 402e elevates an already potent system to new heights. At a staggering 1,400 watts into 2 Ohm loads, the Evolution 403e is a virtually limitless source of power for any speaker. Power is critical for the explosive dynamics that is essential to the home theater experience. This power capability is coupled to a new green operating mode that reduces standby electrical draw to a mere 2 Watts. However, power alone is not the goal as film soundtracks are the emotional vehicles in movies. It is music, not on-screen action, that communicates loss, fear, victory, and determination in movies - think of Rocky, Darth Vader, and Jaws without their theme music. Conveying emotion through music is the true strength of the Evolution 403e and an essential element for stereo and home theater listening.

Power Supply
The Evolution 403e is equipped with two 3,000 VA transformers and 188,000 µF. This power source is the backbone for the output of the Evolution 403e. With this foundation, the Evolution 403e delivers 400 watts into 8 Ohms and 800 watts into 4 Ohms with three channels driven simultaneously. 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. 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 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 usable bandwidth of an Evolution 403e is 300 kHz; 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, -0.17 dB
<0.5 Hz to 125 kHz +0, -3 dB
Signal-to-noise ratio
>106 dB, unweighted, referred to full power output
>116 dB, "A"-weighted
25.4 dB
Total harmonic distortion
<0.02% at 1 kHz, at 400 W, 8 Ohms
<0.15% at 20 kHz, at 400 W, 8 Ohms
Input impedance
Single Ended: 100 kOhms
Balanced: 200 kOhms
CAST: 70 Ohms
Input sensitivity
Single Ended or Balanced: 3.04 V rms
CAST: 3.04 mA rms
Output power
400 W RMS at 8 Ohms
800 W RMS at 4 Ohms
Output voltage
160 V peak-to-peak
57 V RMS
Output current
37 A peak
Slew rate
100 V/µs
Output Impedance
<0.055 Ohms at 20 Hz
<0.064 Ohms, 20 Hz to 20 kHz

Damping Factor (referred to 8 ohms)
>145 at 20 Hz
>125, 20 Hz to 20 kHz

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: 370W) Idle: 570 W
Maximum: 5000 W
Heat Output
Stand-by: 7 BTU/hr. (High-current standby: 1270 BTU/hr.
Idle: 1950 BTU/hr.
Maximum: 7700 BTU/hr.

3 single-ended via RCA connector
3 balanced via XLR connector
3 CAST via 4-pin bayonet connector
3 pairs Krell binding posts
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
Shipped: 190 lb., 86 kg
Unit Only: 175 lb., 79.2 kg


Hi Fi Critic Review
"The overall quality is so well balanced and so even over the frequency range, it's easy to underestimate how good this amplifier is, and one only finds out what might be missing when substituting other references."

Home Theater Review
"It is hands down the best amplifier I've ever heard and the new benchmark..."

  • Evolution 403e
  • Evolution 403e
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