Crown Audio MA-24X6 Advanced Features and Options, Protection Systems, Standby Mode, page

Macro-Tech MA-24X6 & 36X12 Power Amplifiers

4 Advanced Features

and Options

NOTE: For detailed information about these Crown amplifier features, please consult the Crown Amplifier Application Guide, available on the Crown website at www.crownaudio.com

4.1 Protection Systems

Your Crown amplifier provides extensive pro- tection and diagnostic capabilities, including ODEP, IOC., “standby” mode, fuses (or break- ers), and special thermal protection for the unit’s transformers.

4.1.1Output Device Emulation Protection (ODEP)

Crown invented ODEP to solve two long stand- ing problems in amplifier design: To prevent amplifier shutdown during demanding opera- tion and to increase the efficiency of output cir- cuitry.

To do this, Crown established a rigorous pro- gram to measure the safe operating area (SOA) of each output transistor before installing it in an amplifier. Crown also designed intelligent circuitry to simulate the instantaneous operat- ing conditions of those output transistors. Its name describes what it does: Output Device Emulation Protection or ODEP. It not only simu- lates the operation of the output transistors but it also compares their operation to their known SOA. If ODEP sees that more power is about to be asked of the output devices than they are capable of delivering under the present condi- tions, ODEP immediately limits the drive level until it falls within the SOA. Limiting is propor- tional and kept to an absolute minimum—only what is required to prevent the possibility of output transistor damage.

This level of protection enables Crown to increase output transistor utilization while greatly increasing amplifier reliability.

Finally, this onboard intelligence is monitored in two ways. First, the front panel ODEP indica- tors show whether the amplifier is functioning correctly or if ODEP is limiting the drive level. Second, ODEP data is fed to the PIP connector at the back of the amplifier so advanced PIP modules like the IQ-PIP-USP2 can use it to make decisions and control the amplifier.

With ODEP you get the maximum power with the maximum protection—the show goes on!

4.1.2IOC (Input Output Compara-

tor)

The IOC circuit compares the output signal of the amplifier with the input signal. If there is any difference other than gain, then it is consid- ered distortion and the indicator comes on. The LED indicator will come on whenever there is distortion of 0.05% or more. An IOC condition may also be sensed by an IQ PIP module installed in PIP-compatible amplifiers.

IOC is designed to report any form of distor- tion. IOC not only checks the waveform for dis- tortion, but also reports input overload and even a protective action that mutes or shuts down an amplifier. With all of these features, IOC monitors the entire amplifier. When the IOC indicator is off the amplifier is definitely opera- tional and undistorted. IOC provides an on-line proof of performance.

4.1.3 Standby Mode

At the heart of the protection systems is the standby mode which removes power from the

high-voltage supplies to protect the amplifier and connected loads. The standby mode can be identified using the indicator table in Figure 5.2.

Standby mode can be activated in several situa- tions. First, if dangerous subsonic frequencies or direct current (DC) is detected in the ampli- fier’s output, the unit will activate its DC/low- frequency protection circuitry and put the affected channels in standby. This protects the loads and prevent oscillations. The unit resumes normal operation as soon as the amplifier no longer detects dangerous low fre- quency or DC output. Although it is extremely unlikely that you will ever activate the ampli- fier’s DC/low-frequency protection system, improper source materials such as subsonic square waves or input overloads that result in excessively clipped input signals can activate this system.

The amplifier’s fault protection system will put an amplifier channel in standby mode in rare situations where heavy common-mode current is detected in the channel’s output. The ampli- fier should never output heavy common-mode current unless its circuitry is damaged in some way, and putting a channel in standby mode helps to prevent further damage.

The amplifier’s transformer thermal protection circuitry is activated in very unusual circum- stances where the unit’s transformer tempera- ture rises to unsafe levels. Under these abnormal conditions, the amplifier will put the channel of the affected transformer in standby mode. The amplifier will return to normal oper- ation after the transformer cools to a safe tem- perature. (For more information on transformer thermal protection, refer to the following sec- tion.)

page 14 Operation Manual