CAP5: Five-way protection system

Cambridge Audio has developed a proprietary protection system to ensure reliability and long life of its amplifiers. This protection system comprises five main protection methods:

1. DC detection

Indicator – Unit has switched off during operation, protection LED constantly flashes in single bursts.

Description – CAP5 offers loudspeaker protection if the output of the amplifier 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 amplifier 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 flashes 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 amplifier will automatically switch into a fault mode. 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 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 flashes 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 amplifier against short-circuits on the speaker terminals during use.

Remedy – The amplifier 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 amplifier, causing the load resistance to drop too low, the amplifier 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 flashes 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 – Volume is nudged down 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 briefly goes 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 nudged down until CAP5 detects an undistorted output.

The clipping detection is disabled by default. However, to enable the clipping detection, hold down the Standby/On button during power up (whilst switching on the unit at the rear panel power switch). The unit will indicate this by flashing the protection LED for several seconds.

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Cambridge Audio 550A, 650A user manual CAP5 Five-way protection system
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550A, 650A specifications

Cambridge Audio, a revered name in the audio industry, is renowned for producing high-quality amplification solutions. Among its distinguished lineup, the 650A and 550A integrated amplifiers stand out for their exceptional performance and innovative features, making them favorites for both audiophiles and casual listeners.

The Cambridge Audio 650A amplifier is designed to deliver powerful and precise sound, harnessing a robust 75 watts per channel into 8 ohms. This amplifier features an advanced toroidal transformer, which enhances efficiency and reduces electromagnetic interference, ultimately providing cleaner audio. The 650A employs Cambridge's proprietary Class A/B amplifier technology, ensuring a rich and warm sound signature that appeals to lovers of diverse music genres. Additionally, the inclusion of a high-quality headphone output allows for a private listening experience with minimal signal degradation.

In contrast, the 550A model offers a more straightforward approach while still maintaining impressive audio fidelity. Delivering 50 watts per channel into 8 ohms, the 550A is perfect for smaller setups or compact spaces. Its Simple and elegant design hides sophisticated technologies aimed at achieving high-performance output. The amplifier features a high-quality pre-amp section, making it versatile enough to accommodate various audio sources, including vinyl players, CD players, and digital streaming devices.

Both amplifiers feature a solid metal chassis that minimizes vibrations, preserving sound integrity. They also come equipped with multiple inputs, allowing users to connect different sources easily. The 650A and 550A include tone controls to customize the sound signature according to personal preferences, and discrete circuit design to enhance signal clarity further.

Additionally, both amplifiers showcase Cambridge Audio's commitment to user-friendly design principles. With intuitive controls and a clear display, users can enjoy a hassle-free experience, whether adjusting settings or switching sources.

In conclusion, the Cambridge Audio 650A and 550A integrated amplifiers exemplify the brand's dedication to high-quality audio performance. With advanced technologies, robust power, and versatile connectivity, these amplifiers cater to a broad range of listening preferences and environments, ensuring that music is experienced as the artist intended. Whether opt for the powerful 650A or the conveniently efficient 550A, users can expect an unparalleled audio experience that elevates their musical journey.
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