Krell Chorus 4200 XD Multi-Channel Amplifier
Krell’s New XD™ Technology
Krell’s XD (Xtended Dynamics, Dimensionality & Detail) upgrade
for the iBias amplifiers takes an already great sounding amplifier and raises
its performance to the next level. XD is a classic example of Krell’s
continuous R&D efforts reaping benefits across multiple product lines.
During the development of the K-300i Integrated Amplifier we discovered
substantial sonic improvements by lowering the output impedance below
traditional norms. When applying this technique to our existing line of
amplifiers, the improvement was so substantial, it deserved its own, unique
It was no simple matter merely lowering the output
impedance. This affects the amplifier’s stability and transient response, so
each stage prior to the output stage had to be re-tuned to work optimally with
the lower output impedance. This lower output impedance exerts more control
over the speaker drivers, and damps out unwanted vibrational modes—allowing a
more accurate reproduction of the original signal.
Krell Class A iBias™ Technology
Krell’s history is rich with breakthrough Class A amplifiers
that have helped build the Krell legacy of offering the best sounding
amplifiers available. Our revolutionary, patent pending circuit delivers true
Class A operation without the excessive heat and wasted energy of conventional
Power Supply Highlights
Power supply technology has always been an important
contributor to the Krell sound. The power supplies of our Krell iBias Class A
amplifiers have been optimized for use with the iBias circuit. Depending on the
model, up to four toroidal transformers feed amplifier modules that include the
audio circuitry, rectifier, and power supply filtering mounted to an individual
heat sink. This design shortens the electrical path from the power supply to
the output transistors, reducing the overall impedance and allowing the circuit
to respond faster and control the speakers even better and more accurately.
Unlike traditional Class A amplifiers, iBias Class A amps
have a compact design that allows rack-mounting, making them ideal for custom
installation as well as traditional audiophile systems. This convenient form
factor is made possible through thermostatically controlled ventilation fans.
The fans used are specifically chosen for quiet operation, and operate at the
speed required to maintain the ideal internal temperature. They run only during
periods of peak energy demand – when the music is at its loudest – so they are
inaudible in normal use.
The new amplifiers include RJ 45 Ethernet connectivity and
an internal web page that is accessible from any smartphone, tablet, or laptop.
Network connectivity brings convenience, monitoring, and reporting to end
users. Amplifier configuration options include display brightness and timeout.
For energy conservation, the amplifiers can be programmed to power off at a
preset time of inactivity. Individual channels can be muted and firmware
updates can be initiated from the web server.
Once the amplifier is connected to a network router with
Internet access, the amplifier’s advanced protection systems are now viewable
on an Internet-connected device. Excessive current, output DC, fan speeds,
short circuit, and overheating are all monitored in real time. If an issue
occurs, the fault is displayed on the front panel and reported on the web
server interface. Emails will automatically be sent to as many as three email
addresses to notify the end user and/or the dealer of the condition.
The new iBias circuitry is built on a foundation of core
Krell circuit technologies. All signal gain is realized in the current domain
using proprietary multiple-output current mirrors with extraordinary open loop
linearity. Each amplifier channel uses all discrete components. There are no
generic integrated circuits or op amps used anywhere. Gain is distributed among
several stages, allowing each to have a large linear operating area.
Audio signal voltages are converted to current at the
amplifier input, and the audio signal remains in the current domain throughout
the entire amplifier.
Current mirrors in the final gain stages use a new output
power device that operates at a 73% higher voltage, delivers almost 10% more
current, and offers 120 watts of additional power handling capability as
compared to other devices.
With this combination, the iBias amplifiers may now deliver
substantially more power while using a smaller footprint. Normally used in
demanding, high-bandwidth video circuits, these transistors allow the design of
gain stages with superb accuracy and very low distortion. The signal path is
fully complementary and fully balanced from input to output. Independent
complementary pre driver and driver stages for the positive and negative output
transistors make the output stages extremely fast and linear. This unique
circuit is impervious to low-impedance or reactive loads; it simply drives any
loudspeaker with absolute confidence, achieving the very best possible sonic
Most amplifiers use coupling capacitors in the signal path
to block DC and prevent damaging offset voltages from reaching your speakers.
Krell amplifiers are fully direct-coupled, with no capacitors in the audio
signal path. This design gives the Krell amplifiers lower internal impedance,
which allows firmer, more precise control of your speakers. It also provides
flatter, more extended low-frequency response, because coupling capacitors not
only block DC but also affect the lowest bass frequencies. Krell employs
expensive, non intrusive DC servos that remove DC without impacting the musical
signal. Thus, the iBias Class A amplifiers deliver the full breadth of the
music with detail, impact and space intact.
Everything Audiophiles and Home Theater
Enthusiasts Could Want in an Amplifier
Krell iBias Class A amplifiers are the first to deliver the
rich musicality of Class A amplifiers combined with the uncompromised dynamics
of classic Krell amplifiers, and the efficiency and low power consumption of
Class G and H amplifiers.
Because the iBias circuit eliminates crossover distortion, the amplifier is
able to resolve more of the detail and microdynamics in even the best analog
recordings—simply put, the music ‘breathes’. Whether an iBias amplifier is
called on to reproduce the extreme dynamic range of high-resolution digital
files, the minute intricacies of a 45-rpm, 180-gram vinyl record, or the
complexity of today’s latest blockbuster action film, it does so without
altering or abating the music in any way.
The iBias amplifiers’ unprecedented ability to retrieve the
subtlest details gives their sound an incredible dimensionality, with an
ambient, broad and extraordinarily deep soundstage. As spacious as the sound
is, though, the amplifiers are still able to produce pinpoint stereo imaging if
the recording calls for it.
It’s all the power and control for which Krell has always
been famous, with a level of resolution and musicality in the midrange and
treble that has simply never been heard before.
In short, the new patent pending iBias Class A Krell
amplifers give today’s audiophiles and home theater fans everything they could
possibly want in an amplifier.
4 Channel 200 Watt Amplifier Featuring Krell iBias™
20 Hz to 20 kHz +0, –0.08 dB
<0.5 Hz to 100 kHz +0, –3 dB
>95 dB, wideband, unweighted, referred to full power output
>115 dB, “A”-weighted
Total harmonic distortion
<0.04% at 1 kHz, at 200 W, 8 Ω
<0.15% at 20 kHz, at 200 W, 8 Ω
Single-ended: 100 kΩ
Balanced: 200 kΩ
Single-ended or balanced: 1.96 V RMS
Output power 200 W RMS at 8 Ω
360 W RMS at 4 Ω
113 V peak-to-peak
40 V RMS
13.4 A peak
<0.015Ω, 20 Hz to 20 kHz
>530, 20 Hz to 20 kHz, referred to 8W
Standby: 1 W
Idle: 145 W
Maximum: 1680 W
Standby: 3.4 BTU/hr.
Idle: 530 BTU/hr.
Maximum: 6276 BTU/hr.
4 single-ended via RCA connector
4 balanced via XLR connector
4 pairs binding posts
17.1 in. W x 7.65 in. H x 21.10 in. D
434 mm W x 194 mm H x 536 mm D
88 lbs., 40 kg (shipping)
78 lbs., 35 kg (unit only)