Introduction - Cambridge Audio azur 540A Mode D'emploi

INTRODUCTION

Thank y y ou f f or p p urchasing t t his C C ambridge A A udio a a zur s s eries a a mplifier. I I t
is t t he r r esult o o f o o ur m m ost e e xtensive e e ver r r esearch a a nd d d evelopment
program i i n o o ver t t hree d d ecades o o f p p roducing h h igh q q uality a a udio p p roducts.
We h h ope t t hat y y ou w w ill a a ppreciate t t he r r esults a a nd e e njoy m m any y y ears o o f
listening p p leasure.
About t t his a a mplifier
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
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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.