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Cambridge Audio Azur 651W

Stereo power amplifier (Silver)

1 Review

Item # 779651WS

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Our take on the Cambridge Audio Azur 651W

Many digital and network audio components can be used as preamplifiers these days. So instead of connecting them to a separate preamp or receiver, why not connect them directly to a robust power amp like the Cambridge Audio Azur 651W. You'll get the benefits of room-filling, low-distortion power driving your speakers without adding unnecessary, signal-degrading circuitry into the path of your music.

Add real power to your system

Many digital and network audio components can be used as preamplifiers these days. So instead of connecting them to a separate preamp or receiver, why not connect them directly to a robust power amp like the Cambridge Audio Azur 651W. You'll get the benefits of room-filling, low-distortion power driving your speakers without adding unnecessary, signal-degrading circuitry into the path of your music.

With any preamp, the Azur 651W is designed for top-flight musical performance. A large toroidal transformer is the heart of this meaty amp, pushing your speakers to sound their best. The amp's dual mono design offers accurate stereo imaging and a wide soundstage across your listening area. Connect the 651W to the matching Cambridge Audio's Stream Magic 6, and you'll have a fantastic-sounding system with network and digital music options backed by audiophile-grade power.

You'll find balanced XLR and unbalanced RCA inputs on this power amp's rear panel as well as binding posts for two pairs of speakers. A new auto-detect feature allows this amp to turn on and off automatically by recognizing input signals. Trigger, IR, and control bus connections offer several options for integrating operation with separate components and controllers. Cambridge Audio's protection circuitry guards your investment against overheating, short circuits, and clipping.

Product Highlights:

  • 100 watts per channel into 8 ohms
  • 150 watts per channel into 4 ohms
  • stereo balanced XLR and unbalanced RCA inputs
  • large toroidal power transformer delivers clean current with low distortion
  • total harmonic distortion: 0.005% at 20-20,000 Hz
  • signal-to-noise ratio: greater than 90 dB
  • frequency response: 5-80,000 Hz
  • binding posts for two pairs of speakers
  • 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
  • 16-15/16"W x 4-9/16"H x 13-15/16"D
  • weight: 23.5 lbs.
  • warranty: 3 years
  • Our 60-day money-back guarantee

What's in the Box:

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

Cambridge Audio Azur 651W Reviews

Average Customer Review(s):

(1 Review)

Azur 651W: Exceptionally good performance at a reasonable price

Jon H. from Danville, CA on 5/6/2016

Crutchfield Customer Review (What's this?)

The 651W was tested both on the bench with an Audio Precision APx555 and in one of my home listening systems, with a new experimental speaker using a coaxial Midrange/tweeter element. The 651W was primarily purchased as a smaller lighter amplifier to use for driver testing and loudspeaker development, easier to move around and setup than the stalwart Aragon 8008 X3 which has been taking care of those tasks for years, but which weights about 3 times what the 651W weights. On the bench, standard tests show very good performance, swept THD+N at a low 0.005% at 1W output, declining to 0.001% at about 25W output, and dropping even further before reaching the clipping point. This type of curve shows distortion being nearly nonexistent, and this THD+N curve is due to noise dominating the results, yet in this case with the low numbers delivered, the noise is clearly at very low levels. LF distortion and high frequency CCIF two tone IM distortion are similarly excellent. Sonically, the 651W has a very clean presentation, and holds up very well compared with anything remotely close to it's price class- OTOH, it doesn't have quite the weight and control that it's big brother has (851W, or the older 840W), but at less than half the cost, expectations should be reasonable. As an amplifier for the upper range in a bi amplified system, the pe

Pros: Balanced input connectors! (the only way to go..) Very good measured performance on the bench for any price class Clear, well defined midrange and treble, and overall good tonal balance and imaging (with the right front end- recommend the 851D digital preamp at a minimum- used for testing in this case) Very good internal build quality, good overall build quality Good options for system integration for controls, and programmable behavior for standby mode Fairly low standby power

Cons: Not the last word in low frequency control and power, but at this power level and price point, that's to be expected Binding posts are flimsy, difficult to use with spades- work best pulling out the center tip insulators and using locking banana plugs Silver color is nice, the black I bought is OK, but when will they have gold like my iPhone? ;-)


Hands-on research

Product Research


Stereo Amplifier: The Cambridge Audio Azur 651 power amplifier delivers 100 watts x 2 channel into 8 ohms or 150 watts x 2 channel into 4 ohms. The 651W has two pairs of speaker outputs, allowing you to bi-wire a suitable pair of speakers, or to drive two pairs of speakers (A&B) simultaneously.

Toroidal Transformer + Dual Mono Design: The 651W uses an audiophile grade oversize toroidal transformer and substantial extruded heat-sink to deliver perfect power, with extremely low distortion. Cambridge Audio takes separate feeds from the large toroidal transformer and process the left and right amplifier channels separately, effectively making the 651W two mono block amplifiers put together in one chassis. Benefits of this design include:

  • High-quality power output to the amplification circuits, with no clipping of the waveform signal to provide a consistent signal.
  • No transformer noise, buzz, or hum.
  • Dynamic bass performance.
  • High power output to allow large and demanding speakers to be driven at high volume levels.
  • Large power reserves to allow the transformer to deliver high peaks of volume when required.
  • Full shielded against internal and external electrical interference to maintain quality of power and signal.

High-Current Output Transistors: Two pairs of high current output transistors per channel allow the 651W to drive almost any speaker with ease, with excellent bass response and dynamic control.

Balanced & Unbalanced Analog Inputs/Outputs: The Cambridge Audio 651W power amplifier is fitted with both balanced (XLR) and unbalanced (RCA) analog audio inputs to make connection to a Cambridge audio or other manufacturer preamplifier  (sold separately). XLR is a higher-quality input that can reject noise and interference from equipment with balanced outputs.

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.

A&B Speaker Outputs: The Cambridge Audio Azur 651W power amplifier is equipped with two sets of gold-plated, binding-post speaker terminals. The speaker terminals can be used to bi-wire a suitable pair of speaker or to connect two pairs of speakers (A&B). 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 651W power amp features an acoustically damped full-metal chassis with thick brushed aluminum front-panel.

5-Way Protection System: The 651W 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 651W 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 651W 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 651W 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 651W 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

Auto-Detect Mode: The 651W features an Audio Detect mode. When an audio input signal is detected, the 651W will automatically power up. When the audio signal stops, it will then automatically power down after 30 minutes.

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