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. This protection system comprises of five main protection methods:
1. DC detection
Indication - Unit has switched off during operation. The front panel LED light flashes together in the following sequence, one flash with long pause between flashes. 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, please contact your dealer for service.
2. Over temperature detection
Indication - Unit has switched off during operation. The front panel LED light flashes together in the following sequence, two quick flashes with long pause between flashes. 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 - The internal temperature of the output transistors has reached the over temperature limit. Leave the unit for 15 minutes to cool down before pressing the Standby button to resume normal operation.
3. Overvoltage/Overcurrent detection
Indication - Unit has switched off during operation. The front panel LED light flashes together in the following sequence, three quick flashes with long pause between flashes. Read below for more information.
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 switched off during power up. The front panel LED light flashes together in the following sequence, four quick flashes with long pause between flashes. 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. 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.
Remedy - There may be a short circuit between the loudspeaker terminals. Check all loudspeaker connections before attempting to switch the unit out of Standby.
5. Intelligent clipping detection
Indication - Volume is reduced automatically.
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.
Note: The clipping detection is disabled by default. The clipping detection can be enabled in the Setup menu (see 'Setup menu' section).
If CAP5 is persisting, it is also advisable to check the specifications of your speakers to ensure that they are compatible with the CXA61/81. Both amplifiers can be used with speakers with an impedance of between 4 and 8 Ohms.
The CXA61 outputs 60W RMS into 8 Ohms and 90W RMS into 4 Ohms, while the CXA81 outputs 80W RMS into 8 Ohms and 120W RMS into 4 Ohms.
If your connected speakers fall outside of these specifications, then this could also be a reason for CAP5 protection being activated.