Crown Audio CH Series Principles of Operation, CH and CL Series Power Amplifiers, page

CH and CL Series Power Amplifiers

5 Principles of Operation

switch is set to 4/8 Ohm, only the negative and 4/8 ohm connections on the barrier block have audio present. This provides power to low impedance speakers. When the Channel Opera- tion switch is set to 70V, only the negative and 70V connections on the barrier block have audio present. This provides power to distrib- uted speakers in a high-impedance “constant- voltage” application.

The output relay, in conjunction with input sig- nal mute circuit, assures a quiet turn-on and turn-off. In the event of an amplifier output fail- ure, a triac will activate to turn off the offending channel to protect the 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. This point is set both to protect speakers 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 Indicators will blink.

An RJ11 modular jack is mounted on the back panel. Pins 2 and 5 are connected to an opto- isolator which is always in a low-resistance state whenever the unit is on and operational. Should a fault be detected or should the ampli- fier lose AC power, the opto-isolator will

change to a high resistance, 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 at the ampli- fier front end.

The Clip Indicator is driven from the output of the compressor circuitry and lights to indicate the onset of audible distortion.

The Power Indicator 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 electrolytic to form the main power sup- ply. They are protected by the front-panel line circuit breaker and controlled by the front-panel power switch.

BALANCED

INPUT STAGE

Figure 5.2 Models CL1 & CL2 Circuit Block Diagram

page 24 Operation Manual