Cap5 - Five Way Protection System - Cambridge Audio azur 540A Mode D'emploi

CAP5 - FIVE WAY PROTECTION SYSTEM

Cambridge Audio has developed a proprietry protection system to
ensure reliability and a long life to its amplifiers. This protection system
comprises of five main protection methods:
Intelligent c c lipping d d etection
CAP5 has the ability to detect when the amplifier starts to clip or
overdrive its output, which can damage Loudspeakers, the amplifier
power supply and most importantly degrade the sound. When CAP5
detects clipping the volume will be automatically nudged down until
CAP5 detects an undistorted* output (*the volume is nudged down until
the distortion is less than 2% which listening tests have shown is
difficult to hear).
It is possible to disable only this feature by holding down the Standby
button during power up (whilst plugging the unit into the mains power).
The unit will indicate this by flashing the protection LED for several
seconds. Disabling the clipping detection is not advised as this feature
has been added to protect the amplifier.
Over t t emperature d d etection
CAP5 includes temperature detection which constantly monitors the
heat generated by the output transistors. When the monitored
temperature reaches a high level (suitably within the limits of the output
devices) the amplifier will automatically switch into a fault mode
(indicated by double flashing of the protection LED). The unit should
ideally be left for 15 minutes in this state to cool down adequately. If the
unit has not fully cooled down then the temperature may reach the limit
soon after the amplifier is powered up.
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If the Loudspeaker impedance is low the temperature of the amplifier
may rise faster as the amplifier is working harder. If the amplifier is
mounted in a cabinet or the ventilation slots are obstructed the over
temperature detection may activate/reactivate after a short listening
time.
Short c c ircuit d d etection
During power up from standby or during input channel selection 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 stay
in Standby mode until the fault has been removed and Power up is re-
attempted.
DC d d etection
CAP5 offers Loudspeaker protection if the output of the amplifier goes
to DC because of some internal fault. This is a rare fault although it
could just save those expensive Loudspeakers.
If the amplifier is switched out of standby when the input signal to the
amplifier is too high (with the current volume setting) the CAP5 system
will detect this and reduce the volume to a suitable level.
Overvoltage/overcurrent d d etection
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. Many amplifier designers include V/I limiting in the