Crown Audio operation manual Principles of Operation, M Series Power Amplifiers, page

M Series Power Amplifiers

5 Principles of Operation

The output transistors are protected by the Time Dependent Voltage & Current circuit. This cir- cuit protects the devices from extending beyond their safe area of operation, but allows the devices to provide high bursts of peak power with music, allowing your amplifier to deliver more punch. When all is said and done, this amplifier output topology offers a good combination of low quiescent amplifier heating, great distortion performance at high powers, and relative simplicity, with impressive reliabil- ity and value.

For extended flexibility, all of the amplifier’s output power is delivered through the Channel

1Neutrik® Speakon® connector. Both Channel

1and 2 output terminals are wired through the Channel 1 connector, allowing dual or bridge mono applications to be available with one

speaker cable. Refer to Figure 2.3 and Table 1 for Neutrik® Speakon® output pin assign- ments.

The output relay, in conjunction with input sig- nal mute circuit, assures the amplifier will be well-behaved during turn on and off. In the event of an amplifier output failure, a triac will activate to turn off the offending channel and protect your speakers.

The turn on delay circuit functions to keep the output relay open until all the voltages are up and stable, both in the amplifier, and in all the components in the system ahead of the ampli- fier.

Heatsink temperature is monitored by a thermal probe attached to the heatsink. As the tempera- ture rises, the probe sends a proportional cur- rent to the proportional speed fan circuit which starts the fan. Should the power transformer reach its maximum safe temperature, an inter- nal thermal switch opens and the fan circuit turns on full speed to quickly cool down the amplifier. It also disconnects the load via the output relay, removing any output current and further speeding a cool-down cycle. Extra care was taken during the design stage to set this point both to protect your investment and to guard against nuisance tripping.

Whenever the heatsinks or the transformer reach a maximum temperature, or during the normal turn on delay window, the front panel Fault LEDs will blink to get your attention.

A modular RJ-11 jack is mounted on the back panel (similar to the type used on telephones). Pins 2 and 5 are connected to an opto-isolator which is always in a low-resistance state when- ever the unit is on and happy. Should a fault be detected or should the amplifier lose AC power, the opto-isolator will change to a high resis- tance, allowing the user

to remotely detect the status of the amplifier. The Signal Presence Indicators tap the signal chain just before the level controls and prior to the power amplifier chain. They are not ampli- fier output indicators and should only be used to indicate the presence of signal to the ampli- fier front end.

The Clip light is driven from the output of the compressor circuitry and lights to indicate the onset of audible distortion. The Power LED is driven from the low-voltage supply.

A positive and negative regulator form the ±15- volt power supplies. Add to that the main trans- former, a full-wave bridge rectifier, and high energy electrolytics to form the main power supply. They are protected by the front-panel line circuit breaker and controlled by the front- panel power switch.

Operation Manual page 17