Description

Cambridge Audio Azur 640A – Stereo Integrated Amplifier

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 clipping detection

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 temperature detection

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.

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 circuit detection

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 reattempted.

DC detection

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 detection

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 signal path which can degrade the signal by compressing dynamics. The CAP5 system operates outside the signal path and when triggered shuts down the amp rather than limits the size of the signal passing through the amp (signal compression). V/I protects the amplifier against short circuits on the speaker terminals during use.

The 640A builds upon the impressive features of the 540A resulting in a quality of performance you would expect from amplifiers costing considerably more.

This development provides true audiophile levels of sound reproduction and takes the Azur marque to the highest level.

Output is 65 watts per channel into eight Ohms and the inclusion of a Class ‘A’ follower driver stage, together with high quality polypropylene bypass capacitors reflects the attention to detail that sets the Azur 640A apart from its rivals.