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CAP5 - Fiveway protection system
Cambridge Audio has developed a proprietary protection system to
ensure reliability and a long life for its amplifiers and the speakers they
are connected to. Note: Due to the required sensitivity of the CAP5
system, it is possible that mains power disturbances can falsely trigger
CAP5 in extreme situations. This protection system comprises of five
main protection methods:
1. DC detection
Indication - Unit has switched off during operation, display flashes “DC
ERROR”. Press the INFO input select button for a brief on-screen
description and remedy, or read below for more information.
Description - CAP5 offers loudspeaker protection if the output of the
amplifier goes to a high constant voltage (DC) because of some internal
fault. This is a rare fault although detecting it could just save those
expensive loudspeakers.
Remedy - Due to the necessary sensitivity of the DC protection circuit,
extremely hard clipping of the amplifier may cause DC protection to be
triggered. If this fault occurs press the RESET input select button, then
press the Standby/On button to power up again and check operation
with a reduced volume level. If the DC fault occurs again please contact
your dealer for service.
2. Over temperature detection
Indication - Unit has switched off during operation, display flashes
“OVER TEMP”. Press the INFO input select button for a brief on-screen
description and remedy, or read below for more information.
Description - Over temperature is caused by a combination of high
listening levels and low impedance speakers. CAP5 includes
temperature detection which constantly monitors the heat generated
by the output transistors. If the monitored temperature reaches a high
level (suitably within the limits of the output devices) the amplifier will
automatically switch into a fault mode. 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. 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.
Remedy - User related fault. The internal temperature of the output
transistors has reached the over temperature limit. Press the RESET
input select button and leave the unit for 15 minutes to cool down
before pressing the Standby button to resume normal operation.
3. Overvoltage/overcurrent detection
Description - CAP5 offers V/I (voltage/current) 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. The V/I protection
has been incorporated within the amplifier circuitry to provide a fast
response to temporary overload conditions. When the V/I protection is
triggered the unit will continue to operate but distortion may be heard
as the unit protects the output transistors.
Remedy - Reduce the volume. If distortion is still present, check the
speaker connections and ratings.
4. Short circuit detection
Indication - Unit has not come out of Standby, display flashes “SPKR
SHORT”. Press the INFO input select button for a brief on-screen
description and remedy, or read below for more information.
Description - During power up from Standby CAP5 performs a check on
the loudspeaker terminals to see if a short across the terminals has
been accidentally introduced (display flashes “SPKR CHECK”). 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 (display flashes “SPKR SHORT”).
Remedy - User related fault. There may be a short circuit between the
loudspeaker terminals. Press the RESET input select button and check
all loudspeaker connections before attempting to switch the unit out of
Standby (display will flash “SPKR CHECK” then “SPKR OK” when short
circuit fixed).
It is possible to disable the short circuit detection feature by pressing
the SHORT DT button to off when in the 840A V2 System Configure
menu, but it is not recommended. This would only be required if the
loudspeakers have very low DC resistance.
5. Intelligent clipping detection
Indication - Volume is reduced automatically, “CLIPPING” appears on
the front panel display.
Description - CAP5 has the ability to detect when the amplifier starts to
clip or overdrive at its output, which can damage loudspeakers, and
degrade the sound. Clipping distortion
is caused at high volume levels when
the output signal attempts to go
outside the maximum voltage that the
amplifier can provide, causing the tops
of the signal to flatten off. When CAP5
detects clipping the volume will be
automatically reduced down until CAP5
detects an undistorted output.
It is possible to disable the clipping detection feature by pressing the
CLIP DT button to off when in the 840A V2 System Configure menu.
Note: Disabling the clipping detection is not advised as this feature has
been added deliberately to protect the amplifier and loudspeakers.
Clipping
