Cambridge Audio breaks new ground with an entirely new class of amplifier in the shape of the 840A which marks the zenith of Cambridge Audio’s critically acclaimed Azur line-up.

Embracing Cambridge Audio’s patent pending proprietary Class XD™ technology, the 840A brings together the quality of Class A amplification, the power economy of Class B designs, and most amazingly of all, avoids many of the distortion pitfalls inherent in Class AB designs.

Completely separate pre-amp and power amp toroidal transformers and circuits make the 840A effectively a pre and power amplifier combination in one chassis.

Another enormous benefit is its ability to integrate seamlessly with a home cinema system. Fixed level inputs allow the 840A to provide the front channel amplification to systems which use an AV receiver. The receiver continues to provide centre and rear amplification.

In addition to this innovative technology, the 840A uses an extremely sophisticated resistor ladder and relay attenuator for volume control and the same high quality relay switches for input selection. This enables high isolation between inputs, very accurate channel balance and leaves the amplifier completely free from the distortion associated with conventional semiconductor switching and volume control.

As with all Azur products, the foundation of the Azur 840A's is a bespoke chassis. This comprises an incredibly thick 7mm front panel and extruded side panels, both fashioned from aluminium, which combine with a 2mm formed steel base plate and specially designed vibration absorbing feet. The result is an ultra rigid, low resonance, acoustically dampened platform for the electronics to sit int.

The circuit constantly monitors the current in the output stage and the voltage across it. It ensures levels remains within a safe operating area. The CAP5 immediately protects the amplifier should this be exceeded.

Great attention has been paid to ensuring that all functions can be operated from the stunning aluminium-faced Azur Navigator remote. As well as offering full control over all the 840A's features and functions, this neat handset also enables track skip plus play and pause of iPods™ connected to Apple's iPod Universal Dock.

At the core of the 840A’s strength is a patent pending, Class XD (crossover displacement) technology.

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 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, distorted gain transition of a Class AB amplifier.