Cambridge Audio 851A Integrated Class XD Amplifier

SKU 851A

Cambridge Audio 851A Integrated Class XD Amplifier



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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…

Like all Cambridge Audio products, the 851A adheres to our three core values: stunning performance, ease of use and incredible value.

Capable of delivering an enormous 120 watts of high-quality power, it benefits from two audiophile-grade toroidal transformers: one for the sensitive preamp section and one for the power stages allowing the 851A to deliver its immense output without stress. This incredible speaker-taming amount of power can be precision-controlled with another innovation found in the 851A – the new fully balanced silicon gate volume control, which gives very fine adjustment across the volume range and highly accurate channel-balancing.

Because everyone’s needs are different, the 851A offers two main types of connectivity: the more commonly found RCA/Phono inputs, plus two pairs of fully balanced XLR connections. Our matching 851C upsampling CD player also features both types of connection, allowing you to connect your system in the very highest quality possible.

Speaking of flexibility, you can even control your iPhone, iPad or iPod using the 851 Series remote control when they’re docked in our matching iD100 digital dock.

Unlike many high end amplifiers which excel in one area over another, we believe the 851A offers the perfect combination of high performance, flexibility and ease of use. It’s designed to take your listening experience to an entirely different level and we invite you to audition our best amplifier to date at your nearest Cambridge Audio specialist.


Class XD

Class XD, a proprietary Cambridge Audio technology, is a unique amplifier circuit design created to offer the optimum sound quality currently available from existing amplifier configurations, whilst retaining the high power levels required for truly dynamic performance. It was conceived by our London-based engineering team to combine the best of both worlds from Class A and Class A/B amplifier operation.

Class XD (crossover displacement), gives the benefits of pure Class A operation at low levels and eliminates the distortion associated with conventional Class B operation as the fragile audio signal passes though the zero crossing point from transistor to transistor. Distinct from Class AB, XD technology feeds a controlled current into the output stage in such a way that the usual Class B crossover points no longer occur either side of zero volume – the worst possible position in terms of distortion – but displaced to a point where the transfer functions of the transistors are better matched, at a significant output level where it is less audible. The system operates outside of the feedback loop so is not directly involved in the signal amplification itself.
The result is a smooth and linear transition between the two key operating modes, Class A and B.

The benefits of this approach give the sonic refinements of Class A operation and the uncompromising efficiency and power of Class B operation. In fact, the new 851A delivers a gigantic 120 watts per channel – enough for the most demanding speaker set-up.



Class XD amplification designed to eliminate crossover distortion at low signal levels
New balanced volume topology controllable in 1dB steps, giving very fine control, and superbly accurate channel balance
Audiophile grade oversize toroidal transformer and substantial extruded heatsink allowing 2 x 120 Watts RMS into 8 Ohms or 2 x 200W into 4 ohms.
Separate transformer taps for left and right channels, twin rectifiers and separate PSUs for dual mono operation of the left and right power amplifiers
A separate toroidal transformer supplies the preamp making the 851A effectively a Pre and Power amp combination in one box
CAP5 protection technology for trouble free operation
Acoustically damped full metal chassis with thick brushed aluminium front panel
Customisable front panel display
Balanced and unbalanced analogue audio inputs for superior connectivity
RS232 controllable
Eco-friendly <0.5W Standby power consumption
Available in black and silver finishes


Power output 120W RMS into 8 Ohms
200W RMS into 4 Ohms
200W RMS into 4 Ohms
THD (unweighted) < 0.001% 1 kHz at 80% of rated power
< 0.01% 20 Hz – 20 kHz at 80% of rated power
Audio inputs 2 x balanced XLR
8 x RCA inputs
Audio outputs Preamp output
Record output
Frequency Response 10 Hz – 50 kHz +/- 1 dB
S/N ratio (ref 1w):  > 93 dB (ref 1W/8 Ohm)
Input Impedance: Inputs 1 and 2 (balanced) 20 kOhm
Inputs 1-7 unbalanced 20 kOhm
Rec Input 20 kOhm
Power amp damping factor: > 110 at 1 kHz
Max. Power Consumption 800W
Min. power consumption Active (no signal) 70W
Standby power consumption Standby <0.5W
Shelving type
Max bass boost/cut +/- 10 dB at 10 Hz
Max treble boost/cut +/- 7.5 dB at 20 kHz
Dimensions (W x H x D) 430 x 115 x 385mm (16.9 x 4.5 x 15.2”)
Weight 15.0Kg (33lbs)
15.0000 kg

Black, Silver


Class XD


Online, Store

Analogue Inputs

8 x RCA inputs including 2 x Balanced XLR Inputs


Black, Silver

Depth (mm)


Height (mm)


high current output



Cambridge Audio 851A Integrated Amplifier

power output 4 ohm

200 Watts

power output 8 ohm

120 Watts

speaker outputs

A + B Speaker Outputs


Integrated Amplifier

Width (mm)


xlr inputs


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Cambridge Audio has a rich history of developing innovative home entertainment products designed to capture every last drop of detail from your favourite music and movies.

Cambridge Audio