Cambridge Audio 651W User Manual download pdf (Page 10)

Cambridge Audio has developed a proprietary protection system to

ensure reliability and long life of its ampliers. This protection system

comprises ve main protection methods:

1. DC detection

Indicator – Unit has switched off during operation, protection LED

constantly ashes in single bursts.

Description – CAP5 offers loudspeaker protection if the output of the

amplier goes to a high constant voltage (DC). 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,

hard clipping of the amplier may cause DC protection to be triggered.

If this fault occurs please switch the unit off, 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

Indicator – Unit has switched off during operation, protection LED

constantly ashes in bursts of two.

Description – 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 amplier will automatically switch into a fault mode. If the

loudspeaker impedance is low, the temperature of the amplier may rise

faster as the amplier is working harder. If the amplier 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 unit is not damaged, although it should be left for 15

minutes to cool down before being switched out of Standby.

3. Overvoltage/overcurrent detection

Indicator – Unit has switched off during operation, protection LED

constantly ashes in bursts of three.

Description – 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. V/I also protects the amplier against

short-circuits on the speaker terminals during use.

Remedy – The amplier is being used outside its performance envelope.

Reduce the volume. Also check to see if there is a short- or partial short-

circuit between the loudspeaker terminals.

Note: If the indication remains the same and multiple loudspeakers are

being used on each loudspeaker output, then please remove a pair and

retry. If too many loudspeakers are connected to any amplier, causing

the load resistance to drop too low, the amplier will be overdriven. CAP5

will detect this situation. If the indication remains the same with only one

set of loudspeakers connected, there may be a fault with one or both of

the loudspeakers.

4. Short-circuit detection

Indicator – As the unit attempts to come out of Standby mode, the

protection LED ashes in bursts of four.

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 remain in Standby mode

until the fault has been removed and power up is re-attempted.

Remedy – User-related fault. 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

Indicator – Clipping LED will ash if the audio output is at/above the

clipping level.

Description – CAP5 has the ability to detect when the amplier 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 briey goes outside the maximum voltage that

the amplier can provide, causing the tops of the signal to atten off.

Clipping

CAP5: Five-way protection system

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Cambridge Audio 651W User Manual Page 10

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