Cambridge Audio Azur 840W Class XD power amplifier

Posted by Thomas Jones on Wednesday, January 23, 2008 - 06:18 am:

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CES Innovations Awards Honoree - Azur 840W Class XD™ power amplifier -- Suggested retail price - $1900 ex sales tax; £1000/€1900 inc VAT -- Available Spring 2008

Cambridge Audio has taken the Azur 840 series to its peak with the introduction of two new models – the 840E pre-amplifier and 840W power amplifier. The 840W is a high-end power amplifier that has been designed by the same team behind the 840A and uses an evolution of Cambridge Audio’s hugely innovative Class XD™ technology for a highly detailed naturally musical performance. The second generation Class XD is now complemented by a new output stage carefully adjusted to integrate with this novel technology, revised balanced inputs for lower distortion and noise. An awesome 200W @ 8 Ohms gives excellent load driving ability or, a truly massive 500W bridged mono can be harnessed for even ‘difficult’ high-end speakers.

Key features:

• Second generation Class XD™ technology
• Breathtaking 200W @ 8 Ohms and 500W into 8 Ohms bridged mono
• Two pairs of very high current output transistors per channel in revised configuration for improved integration with Class XD
• Twin rectifiers and separate transformer taps for dual mono operation of the left and right power amplifiers
• Oversized low flux toroidal transformer with an enormous 1200VA power rating
• Allows biamp or bridged mono modes
• RCA and balanced XLR connections which are switchable from the rear panel
• Cambridge Audio proprietary CAP5™ protection system
• Side panels incorporate strategic venting to keep the unit cool
• Solid 7mm aluminium front panel plus an ultra rigid, acoustically dampened chassis for extremely low distortion
• Available in silver or black

At the core of the 840W’s strength is a patent pending, Class XD (crossover displacement) technology (first seen in the 840A) and which has been subtly revised following continuing post-launch development and critical evaluation. This unique design gives pure Class A operation at low levels, moving smoothly into an enhanced version of Class B at higher levels. This system should not be confused with Class AB, which inherently generates greater distortion at high levels than a pure Class B design. XD technology feeds a controlled current into the output stage actively displacing the crossover point in a new way so that the usual Class B crossover point no longer occurs at zero volume - the worst possible position in terms of distortion – but at a significant output level. The result is a smooth and linear transition between the two modes of operation, which differs significantly from the abrupt, gain transition of a Class AB amplifier. To facilitate this, the Azur 840W amplifier includes a massive, oversized low flux toroidal transformer, incorporating a silicone-steel screen.

In our ongoing development of Class XD we have conducted exhaustive research into further improvements of our amplifier designs to squeeze everything out of this innovative technique. This in turn led to a new output stage topology being developed which has been incorporated into the 840W. Two pairs of very high current output transistors are used per channel (for the amplifier output) plus an extra high current transistor per channel for the XD circuit.

The 840W can also be used in either bi-amped or bridged mono configurations. When bi-amping, one 840W (of the pair) powers each speaker so that the tweeters and woofers each have their own dedicated amplifier channel. Alternatively the bridged mono mode allows the use of two 840Ws with each configured as a 500 watt monobloc. In fact combinations of the two regimes allow the use of one, two, four or even more 840Ws to be used, taking it to the truly stratospheric high-end.

Also included is the latest development of Cambridge Audio’s proprietary CAP5 protection system. CAP5 (Cambridge Audio Protection 5) is an innovative and intelligent protection system. It constantly monitors the amplifier, without degrading signal purity, ensuring ultimate reliability. There is also short-circuit detection and a solid-state temperature sensor with over-heat cut out to ensure the amplifier delivers high performance.

All this proprietary engineering is housed within our low resonance, acoustically dampened chassis which includes a 7mm thick aluminium front panel.