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 Evolution 400


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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 Gain
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/ÎĽs   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
Standby: 150 W
Idle: 210 W
Maximum: 2500 W Heat output
Standby: 510 BTU/hr.
Idle: 720 BTU/hr.
Maximum: 3800 BTU/hr. Inputs
1 single-ended via RCA connector
1 balanced via XLR connector
1 CAST via 4-pin bayonet connector Outputs
1 pair Krell binding posts Dimensions
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 Weight
120 lbs., 54.3 kg (shipping)
102 lbs., 46.2 kg (unit only)





The Evolution 400 amplifier is
the lowest powered 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 400
shares the same sophisticated circuit topologies as its larger siblings
but packs it into a smaller chassis. The Evolution 400 is perfect for
when high performance is critical but space is at a premium.

Power Supply

The Evolution 400 is equipped with a massive 4,000 VA transformer. This
power source is the backbone for the output of the Evolution 400. With
this foundation, the Evolution 400 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%
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
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.