Class XD Amplification: Cambridge Audio's proprietary XD amplification
system switches dynamically between Class A and AB systems. Class A
amplification delivers the purest possible sound, using only one transistor to
conduct, but can be energy inefficient. Class AB involves both transistors
conducting simultaneously, but makes it impossible to maintain a balance of low
crossover distortion and power efficiency. Cambridge Audio's Class XD system
operates in both Class A and Class AB mode, dynamically moving the crossover
point depending on the audio output volume. Cambridge Audio's Class XD
amplification with 12 output transistors per channel combines the near zero
crossover distortion of pure Class A with improved efficiency of Class AB at
higher volumes, without any compromises in performance.
Stereo & BridgeD Modes: The Cambridge Audio Azur 851W delivers a
massive 200 watts x 2 channel into 8 ohms (or 350 watt x 2 channel into 4 ohms)
in stereo configuration, but can also be run in bridged mono mode to output 500W
x 1 channel into 8 ohms (or 800 watts x 1 channel into 4 ohms). There is a
switch on the back of the amp which selects between Stereo or Bridged (mono)
Dual Toroidal Transformers: Separate, high-end transformers for the
power amplifier and input and other circuitry ensure audio performance is
unaffected by the dramatic current output swings required to drive demanding
speakers, by keeping power supplies entirely separate.
Terrapin Impedance Buffering Modules: Cambridge Audio's proprietary
modules replace the op-amps commonly found in similar amplifiers. At the
critical low level gain stages, these offer far improved stereo separation and
Balanced & Unbalanced Analog Inputs/Outputs: The Cambridge Audio
851W power amplifier is fitted with both balanced (XLR) and unbalanced (RCA)
analog audio inputs to make connection to Cambridge Audio's 851E preamplifier (779851EB,
sold separately) or other manufactures preamp (sold separately). XLR is a
higher-quality input that can reject noise and interference from equipment with
balanced outputs. Both the unbalanced and balanced inputs have loop outputs that
can be used with the 851W's Bi-Amp Mono and Bridged-Mono modes to allow two or
more 851Ws to be used in a very high-quality audio system.
Note: Only one type of input (balanced or unbalanced) can be used. There
is a switch on the back panel of the amp which selects between the balanced or
Binding Post Speaker Outputs: The Cambridge Audio Azur 851W power amplifier
is equipped with two sets of gold-plated, binding-post speaker terminals. The
speaker terminals can be used in a Normal Stereo, Bi-wire Stereo, Bi-amp Mono,
or Bridged Mono configuration. The binding-post terminals will accept bare wire
(up to 10AWG), pin-connects, and banana plugs (dual or single). Only connect
speakers with a nominal impedance of 4- to 8-ohm.
All-Metal Chassis: The Cambridge Audio 851W power amp features an
acoustically damped full-metal chassis with thick brushed aluminum front-panel.
5-Way Protection System: The 851W benefits from the latest
version of Cambridge Audio's sophisticated proprietary protection system. CAP5
(Cambridge Audio Protection 5-way) is an innovative and intelligent circuit that
constantly monitors the amplifier, without degrading signal purity, ensuring
ultimate reliability. Designed to protect the amp in operation, the system has
been developed to leave sound quality unaffected. It incorporates a clipping
sensor that reduces the volume to keep levels in a safe range, short-circuit
detection, and current and voltage overload detection plus a solid-state
temperature sensor for over-heat cut out. Combined, these technologies ensure
that Cambridge Audio amplifiers will go on to deliver years of reliable,
- DC Detection: CAP5 offers loudspeaker protection if the
output of the amplifier goes to a high constant voltage (DC).
- Over Temperature Detection: AP5 includes temperature
detection which constantly monitors the heat generated by the output
transistors. If the monitored temperature reaches a high level (suitably
within the limits of the output devices) the amplifier will automatically
switch into a fault mode.
- Over Voltage Detection: CAP5 offers V/I protection by
constantly monitoring the output transistors to keep them working inside
their Safe Operating Area (SOA). The SOA is a set of limits given by the
output transistor manufacturer to ensure reliability. V/I also protects the
amplifier against short-circuits on the speaker terminals during use.
- Short-Circuit Detection: During power up from Standby,
CAP5 performs a check on the loudspeaker terminals to see if a short across
the terminals has been accidentally introduced. If the resistance measured
across the loudspeaker terminals is too low, the unit will remain in Standby
mode until the fault has been removed and power up is re-attempted.
- Intelligent Clipping Detection: CAP5 has the ability to
detect when the amplifier starts to clip or overdrive at its output, which
can damage loudspeakers and degrade the sound. Clipping distortion is caused
at high volume levels when the output signal briefly goes outside the
maximum voltage that the amplifier can provide, causing the tops of the
signal to flatten off. When CAP5 detects clipping, the volume will be
automatically nudged down until CAP5 detects an undistorted output.
IR Input/Control Bus: The 851W also features a IR Emitter input (3.5mm) which allows modulated IR
commands from multi-room systems or IR repeater system to be received by the
amplifier. In addition, the 851W features a Control Bus Input and Output (RCA),
which allows un-modulated commands from multi-room systems or other components
to be received by the amp and loop out to another unit.
Trigger Input/Output: For custom install use or with preamps and with
trigger outputs, the 851W can be turned on and off (i.e. brought in and out of
Standby mode) by the presence of 5-12V DC at the Trigger input (3.5mm). A
trigger input will also produce an internally generated 12V DC trigger output at
the Output/Thru connection (3.5mm). Turning the 851W on from the front panel
also produces a 12V DC trigger output at the Output/Thru connection. This can be
used to turn on/Standby other connected power amplifiers or other equipment if
Smart Auto-Standby: Smart Auto-Standby mode (<0.5W) detects incoming
audio signals to simplify integration with Cambridge Audio preamplifiers.