Cambridge Audio Azur 851W

Stereo power amplifier (Silver)

Item #: 779851WS

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More than just brawn

Pure power. When it comes to music, it's about more than sheer brute force. A power amp should take great care in delivering music to your speakers. That's the strength of the Cambridge Audio Azur 851W. Sure, it packs plenty of muscle with 200 watts per channel driving 8-ohm speakers. But the real magic is how it delivers that load — by preserving the purity of the signal through a sophisticated design made for audiophiles seeking sonic perfection.

Combining Class A and AB

The Azur 851W uses Cambridge Audio's proprietary Class XD™ power system. It combines the unimpeachable sound quality of Class A amps with the efficiency of Class AB technology. That means you get fantastic sound with minimal crossover or switching distortion from an efficient amp that doesn't run too hot. The 851W's power is generated by not one, but two toroidal transformers. One is purely dedicated to the power amp stage, while the other handles the input stage as well as the rest of the amp's circuitry. That gives this amp the dexterity to handle dramatic changes in dynamics as well as high output levels for when you want to rock the rafters.

Cambridge Audio Azur 851W 2-channel power amplifier

The Azur 851W offers lots of connection options, including XLR inputs, 4 pairs of binding posts for bi-wiring speakers, and plenty of integrated control possibilities.

Sonic synergy with your preamp

Cambridge Audio's innovative Terrapin amp modules forms an impedance buffer between the incoming source signal and the amplifier stage of the 851W. This ensures accurate signal transfer from preamplifier to power amp, offering optimum performance and very low distortion with a wide variety of preamps. Of course, Cambridge Audio's Azur 851E preamplifier is the ideal mate for the 851W if you're looking for matching components with integrated control features.

Stereo, bi-amp, and bridged mono modes

You'll find balanced XLR and unbalanced RCA inputs on this power amp's rear panel as well as speaker terminals for single- or bi-wired connections. There's also a switch that lets you configure multiple 851Ws for bi-amping your speakers or bridging them for use as monoblock amps pushing a whopping 500 watts per channel into 8-ohm loads. A new auto-detect feature allows this amp to turn on and off automatically by recognizing input signals. Cambridge Audio's protection circuitry guards your investment against overheating, short circuits, and clipping.

Product Highlights:

  • 200 watts per channel into 8 ohms
  • 350 watts per channel into 4 ohms
  • selectable stereo (single- or bi-wired), bi-amp (mono) and bridged mono modes
  • bridged mono mode delivers 500 watts x 1 into 8 ohms (800 watts x 1 into 4 ohms)
  • stereo balanced XLR and unbalanced RCA inputs
  • proprietary Class XD amplification incorporates Class A and AB designs for signal purity, low crossover distortion, and improved efficiency
  • 2 toroidal power transformers; 1 for the power amp stage, 1 for input stages and other circuits
  • proprietary Terrapin amplification stages offer improved stereo separation and imaging at low volume levels and consistent sound from all source components
  • total harmonic distortion: 0.005% at 20-20,000 Hz
  • signal-to-noise ratio: greater than 90 dB
  • frequency response: 5-80,000 Hz
  • auto-standby mode detects incoming audio signals for easy integration with a preamp
  • infrared control input, control bus in/out, and 12-volt trigger in/out for integration with external control systems and components
  • all-metal chassis with aluminum front panel to minimize vibration-induced distortion
  • CAP5 proprietary protection system prevents overheating and clipping
  • 17"W x 5-7/8"H x 14-1/2"D
  • weight: 42.2 lbs.
  • warranty: 3 years
  • Our 60-day money-back guarantee

Cambridge Audio Azur 851W Reviews

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851W Kicks A$$!

Written By Jim R, Florida on Thursday, March 05, 2015

Crutchfield Customer Review (What's this?)

Wow! Wow! Wow! This amp brings it all to life! I WILL be adding a second!

Pros: The clarity is amazing! The power is awesome!

Cons: None

Hands-on research

What's in the box?

Download owner's manual

  • Power amplifier
  • 6' AC power cord
  • 38" Mono-RCA cable
  • User Manual (En/Fr/Sp)
  • Quick Start Guide (En/Fr/Sp)

Product Research


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) mode.

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 imaging.

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 unbalanced inputs.

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, high-performance sound.

  • 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 desired

Smart Auto-Standby: Smart Auto-Standby mode (<0.5W) detects incoming audio signals to simplify integration with Cambridge Audio preamplifiers.

Our Product Research Team

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