INTRODUCTION

Thank you for purchasing this Cambridge Audio azur series amplifier. It is the result of our most extensive ever research and development program in over three decades of producing high quality audio products. We hope that you will appreciate the results and enjoy many years of listening pleasure.

About this amplifier

The design of any purist audio amplifier is mainly centred on two main areas, the Power Supply and the driver stage's ability to drive the output stage effectively. We at Cambridge Audio have researched the best possible ways to achieve the highest performance in these areas, at a sensible price. The Azur 540A/640A topology uses the same tried and tested output devices that Cambridge Audio have used in previous award winning amplifier models, but many hours of research have gone into the study and development of the preceding stages. This driver circuitry is essentially a matched differential input pair, loaded by a current mirror and driven from a transient compensated current source driving a high beta cascoded voltage gain stage. The thermally compensated output stage is setup to inherently give optimum Class AB conditions (for greatly reduced cross over distortion caused by dynamic heating of the output dies). In addition the topology includes a further improvement to the driver stage consisting of a pure class-A follower to isolate the voltage amplifier transistors from the difficult loading of the output transistors. This increased current drive to the output stage combined with a novel transient feed forward circuit doubles the slew rate to 40V/uS.

Due to critically refined circuit board layouts, careful component placement and short signal paths the stability of these amplifiers is extremely high which allows the compensation components to be

reduced in size. This has the effect of reducing distortion, increasing dynamics and allowing the bandwidth to be opened up to a massive 80kHz, ideal for the new 'better than CD' high bandwidth sources such as DVD-Audio and Super Audio CD.

The performance of any amplifier is limited by the dynamic abilities of its power supply, and for this reason Cambridge Azur amplifiers incorporate many features, including a low flux toroidal transformer, paralleling of the reservoir capacitors and careful use of bypass capacitors, to allow the instantaneous clean delivery of charge whenever it is needed. This ensures an open and natural sound being reproduced and ensures a positive response to any dynamics or sudden transients in the signal being reproduced.

Particular attention has also been paid to the quality of the passive components which have been carefully chosen for their sonic benefits. The Azur 640A in addition uses high grade Polypropylene signal bypass capacitors to improve signal flow and dynamics.

The Cambridge Audio Azur 540A and 640A amplifiers also incorporate tone controls, which may be switched out of circuit in 'direct' mode for the shortest and therefore purest signal path. Other features include 24k gold plated phono sockets, dual tape loops, pre amp output, a headphone socket and a secondary set of high level loudspeaker terminals.

An important feature which has been included as standard on both the 540A and 640A is the new innovative Cambridge Audio designed CAP5 protection system. This consists of a microprocessor which constantly monitors the amplifier providing comprehensive protection against a variety of possible faults. This has been achieved without adding any active circuitry into the signal path to degrade the sound or the dynamic abilities of the amplifier.

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Cambridge Audio 540A user manual Introduction, About this amplifier
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540A specifications

Cambridge Audio has established itself as a formidable force in the realm of high-fidelity audio equipment, and the 540A and 640A amplifiers exemplify the company's commitment to delivering exceptional sound quality at a competitive price point. These integrated amplifiers, known for their detailed sound reproduction and robust performance, cater to audiophiles who appreciate both quality and value.

The Cambridge Audio 540A is part of the company's entry-level range, designed for music enthusiasts seeking an affordable yet high-performance amplifier. The 540A boasts a powerful 50 watts per channel output, allowing it to drive a variety of speaker types with ease. The design emphasizes simplicity and user-friendliness, featuring straightforward controls and a sleek finish that fits well in any audio setup.

One of the standout features of the 540A is its dual-mono circuit design. This architecture minimizes crosstalk and signal interference, allowing for a cleaner, more precise sound. It also incorporates high-quality components, including a toroidal transformer, which contributes to improved efficiency and reduced distortion. Additionally, the amplifier features a range of inputs, including multiple line-level options, making it versatile enough to accommodate various audio sources such as CD players, turntables, and streaming devices.

On the other hand, the 640A is an upgrade that builds upon the strengths of the 540A. With a more powerful output of 75 watts per channel, the 640A is designed for users who demand more from their audio systems. This amplifier incorporates an improved power supply and enhanced components, further refining the sound quality. The 640A also introduces features such as a high-quality phono stage, enabling direct connection to turntables without the need for separate equipment.

Both amplifiers incorporate Cambridge Audio's dedication to quality with a focus on analog circuitry. This is particularly evident in the warm, rich sound signature that these amplifiers provide, making them ideal for a range of music genres. The build quality is robust, with a solid chassis designed to reduce vibration and resonance, ensuring a stable platform for audio performance.

In summary, the Cambridge Audio 540A and 640A amplifiers offer a compelling combination of sound quality, versatile connectivity options, and robust design. Whether you are an entry-level audiophile or a seasoned listener looking for an upgrade, these amplifiers provide an engaging listening experience that highlights the nuances and details of your favorite music. With Cambridge Audio's unwavering focus on high-fidelity sound, both models are captivating choices that continue to impress users worldwide.
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