Krell CHORUS 7200 XD 7-Ch Power Amp With IBias Tech

Krell CHORUS 7200 XD 7-Ch Power Amp with iBias Tech

Featuring the KRELL XD Upgrade

The “XD” upgrade for the Chorus/Duo/Solo amplifiers reduces
the output impedance to less than half of its original value. This lower output
impedance better damps unwanted speaker vibrational modes. Changing the output
impedance also necessitated re-compensating each amplifier stage to achieve
optimal critically damped transient response. This ensures that the amplifier
accurately follows the dynamics of the input signal.

7 Channel Power
Amplifier

200 Watt Amplifier
Featuring Krell iBias Technology

Frequency response
20 Hz to 20 kHz +0, –0.08 dB
<0.5 Hz to 100 kHz +0, –3 dB

Signal-to-noise ratio
>95 dB, wideband, unweighted, referred to full power
output
>115 dB, “A”-weighted

Gain
26.2 dB

Total harmonic
distortion
<0.04% at 1 kHz, at 200 W, 8 Ω
<0.15% at 20 kHz, at 200 W, 8 Ω

Input impedance
Single-ended: 100 kΩ
Balanced: 200 kΩ

Input sensitivity
Single-ended or balanced: 1.96 V RMS

Output power
200 W RMS at 8 Ω
360 W RMS at 4 Ω

Output voltage
113 V peak-to-peak
40 V RMS

Output current
13.4 A peak

Slew rate
40 V/μs

Output impedance
<0.038 W, 20 Hz to 20 kHz

Damping factor
>210, 20 Hz to 20 kHz, referred to 8 W

Power consumption
Standby: 1 W
Idle: 255 W
Maximum: 2800 W

Heat output
< Standby: 3.4 BTU/hr.
Idle: 873 BTU/hr.
Maximum: 9590 BTU/hr.

Inputs
7 single-ended via RCA connector
7 balanced via XLR connector

Outputs
7 pairs binding posts

Dimensions
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

Weight
110 lbs., 50 kg (shipping)
100 lbs., 45.4 kg (unit only)

 

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. Audiophiles have always considered Class A technology to
be the best sounding operating state for amplifiers. However, despite Class A’s
unrivaled sound quality, it has fallen out of fashion because of recent demands
to reduce power consumption and heat in home electronics products. Krell
engineering took this challenge and redefined the meaning of high performance
power amplifier. Our goal – unmatched performance, elegant design, and a
compelling array of features. The breakthrough – a patent pending circuit
delivering Class A operation without the excessive heat and wasted energy of
conventional designs, housed in a striking new form factor, with network
connectivity for advanced access and monitoring. The sound is open and
unconstrained, in a manner that rivals live performance and the true sound of
voices and instruments. Music and dialogue are reproduced with a richness,
detail, and startling dynamics that fill a room.

Plainly stated, Class A designs are the most musically
accurate circuit topology available. Class A amplifiers do not suffer from the
inherent distortions that all Class AB amplifiers experience. In a traditional Class
A design, the output transistors conduct full current at all times regardless
of the actual demand from the speakers. Often, only a fraction of this power is
needed to reproduce an audio signal at normal listening levels. The rest of the
power is dissipated through the amplifier’s heat sinks, producing large amounts
of wasted heat. With Krell’s iBias™ technology, bias is dynamically adjusted,
so the output transistors receive exactly as much power – but only as much
power – as they need.

Krell’s iBias Class A technology allows our latest
amplifiers to run in full Class A mode to full power while minimizing heat
generation. Previous efforts at using a “tracking” bias, while
effective, only measured the incoming signal and set bias levels from this information.
Our new patent pending iBias technology significantly elevates the
effectiveness of previous designs by calculating bias from the output stage.
This seemingly small change in topology results in a dramatic improvement in
sound quality, especially midrange richness and purity.

The core of the technology is an innovative, patent pending
design for a dynamic intelligent bias circuit. Our iBias Class A circuit
directly measures the output current of the amplifier and adjusts the bias to
the optimum level. Because iBias Class A measures the output current, the real
time demands of the specific speaker connected to the amp are directly
incorporated into the circuit function. In addition, iBias Class A even reduces
the bias when the signal is at very low levels, making its operation undetectable
by ear and even by standard amplifier measurements.

In sliding bias schemes, the circuit merely estimates how
much bias is needed based on the input signal and an “assumed speaker
load.” Compared with iBias Class A, these sliding bias technologies are
much less effective – and much less accurate.

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.

Network Connectivity

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.

Circuitry Highlights

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
results.

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 Fans Could Want
in an Amplifier

Krell iBias Class A amplifiers are the first to deliver the
rich musicality of Class A amplifiers, 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.