Cambridge Audio 851W Stereo Power Amplifier


When Cambridge Audio set about developing their 851 Series of hi-fi separates, the brief was simple: to make a hi-fi that not only sounded better than anything else out there, but one that was flexible enough to meet the needs of every serious music lover. With this in mind Cambridge Audio created a system capable of delivering stunning results from all your music whether it's stored on CD, vinyl, your computer, or even your phone.

Developed at Cambridge Audio's R&D centre in London, the 851 Series offers the perfect balance of powerful performance, amazing levels of detail, and innovative features designed to tease the best from your music, however you choose to listen.

Perhaps most importantly, the 851 Series has been developed as a complete system with complementing features and synergies. Not only does this give you the very best balanced system, but one that's incredibly easy to use despite its impressive technical performance.

The 851 Series has also been developed strictly to Cambridge Audio's famous Sound First design principles. The core aim of the series is to reproduce your music as faithfully as possible – nothing else matters. We believe the 851 Series achieves that and the critics seem to agree. Now it's your turn to listen and judge for yourself…



The Azur 851W improves over its already highly respected predecessors in just about every way. At its heart is Cambridge Audio's innovative and proprietary Class XD system, with 12 output transistors per channel. Combining the best of Class A and Class AB and removing the downsides of both, Class XD amplification eliminates crossover distortion like a Class A amp, while offering the power efficiency of Class AB. Its performance has to be heard to be believed.

As well as proprietary Class XD amplification, the 851W uses separate high-end toroidal transformers one for the power amplifier itself and one for input and other circuitry, for a performance unaffected by audio output volume or dynamics. It also uses our proprietary Terrapin impedance buffering modules to separate amplifier and signal impedance for absolutely consistent sound across sources. And CAP5 proprietary protection to avoid DC spikes, overheating, short circuits or clipping.

The result is a stunningly accurate amplifier that's also amazingly powerful and versatile. The 851W offers a massive 200W per channel into 8 Ohms in stereo configuration, but can also be run in bridged mono mode to output 500W RMS per amplifier used.

New touches also include a smart auto-standby mode that detects incoming audio signals, automatically coming out of its energy efficient (<0.5W) standby mode and simplifying integration with any Cambridge Audio preamplifier, such as the stunning 851E.

Powerful, precise and flexible – but most important of all, the best sounding amplifier we've ever made. Prepare to be impressed…



Class XD amplification – Cambridge Audio's proprietary 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. Our Class XD system operates in both Class A and Class AB mode, dynamically moving the crossover point depending on the audio output volume. This combines the near zero crossover distortion of pure Class A with improved efficiency of Class AB at higher volumes, without any compromises in performance for the best of both world.

Serious power – 200W into 8 Ohms stereo mode is serious power. But for those with bigger plans, the 851W is usable in a mono bridged configuration with each amplifier delivering 500W RMS.

Two 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 – unheard of at this price point.

CAP5 proprietary protection – Protects the integrity of your system by avoiding DC spikes, overheating, short circuits or clipping.

Integration – Smart auto-standby mode detects incoming audio signals to simplify integration with Cambridge Audio preamplifiers.

All-metal chassis – Including extensive use of aluminium to create massive structural rigidity, careful damping and control of acoustic resonance.



Cambridge Audio's Class XD amplification with 12 output transistors per channel combines the best of Class A and AB amplification
Separate toroidal transformers for power amp and input/other circuitry
Cambridge Audio's Terrapin impedance buffering modules – separating amplifier and signal impedance
200W into 8 Ohms stereo mode or 500W RMS per amp mono bridged mode
Cambridge Audio's CAP5 protection from DC spikes, overheating, clipping etc.
<0.5W smart auto-standby mode for integration with preamplifiers
All metal chassis with premium components, creating massive structural rigidity, careful damping and control of acoustic resonance.
Remote Control – Compatible with the entire 851 range



Power output – stereo/mono200W per channel into 8 Ohms
350W per channel into 4 Ohms
Power output – bridged mono500W 8 Ohms
800W 4 Ohms
THD (unweighted)< 0.001% 1 kHz
< 0.005% 20 Hz - 20 kHz
Frequency response5Hz – 80kHz
S/N ratio (ref 1W / 8 Ohn)>90dB (unweighted)
Sensitivity – stereo or mono1.5V rms unbalanced
1.5 + 1.5V rms balanced
Sensitivity – bridged mono0.775V rms unbalanced
0.775V + 0.775V rms balanced
Input impedancesBalanced input 38 kOhm
Unbalanced input 68 kOhm
Power Amp damping factor> 110 at 1 kHz
Max. power consumption2400W
Standby power consumptionStandby <0.5W
Dimensions (H x W x D)148 x 430 x 365mm (5.8 x 16.9 x 14.4”)
Weight19.1kg (42.2lbs)
Cambridge Audio

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