5 Advanced Features
and Options
5.1 Protection Systems
Macro-Tech amplifiers provide extensive pro- tection and diagnostics capabilities. Protection systems include ODEP, "standby" mode, fuses (or breakers), and special thermal protection for the unit's transformers.
5.1.1 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 the output circuitry.
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. Next, Crown 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. In addition to simulating the operating conditions of the out- put transistors, it also compares their operation to their known SOA. If it sees that more power is about to be asked of them than they are capa- ble of delivering under the present conditions, ODEP immediately limits the drive level until it falls within the SOA. Limiting is proportional and kept to an absolute minimum—only what is required to prevent output transistor damage.
This level of protection enables Crown to increase output efficiency to never-before- achieved levels while greatly increasing ampli- fier reliability.
The on-board intelligence is monitored in two ways. First, the front panel ODEP indicators show whether the amplifier is functioning cor- rectly or if ODEP is limiting the drive level. Sec- ond, ODEP data is fed to the back panel PIP connector so advanced PIP modules like the IQ-PIP-USP3 can use it to monitor and control the amplifier.
With ODEP, the show keeps going because you get the maximum power with the maximum protection.
5.1.2 Standby Mode
An important part of a Macro-Tech amplifier's protection systems is standby mode. Standby protects the amplifier during potentially cata- strophic conditions. It temporarily removes bias in all four output stages, protecting the amplifier and its loads. This advanced protec- tion implementation, called "Quad-Mute," is new to the Macro-Tech series amplifiers. Standby mode can be identified using the indi- cator table in Section 6, Troubleshooting.
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 section 5.1.3.)
An IQ-PIP module may also temporarily place the amplifier in standby mode, typically for power conservation. The standby mode status can be triggered manually. The auto standby can be triggered via the control software, in which case the standby status will be automati- cally cancelled when the defined level of input signal is detected. If the unit has been placed into a standby state, not auto-standby, this sta- tus must be manually cleared using either IQwic or System Architect control software.
5.1.3Transformer Thermal Protec-
tion
The Macro-Tech 2402 has transformer thermal protection. It protects the power supplies from damage under the rare conditions of trans- former temperatures rising too high. A thermal switch embedded in each transformer removes power to the channel if there is excessive heat. The switch automatically resets when the trans- former cools to a safe temperature.
It is extremely unlikely that you will ever see a Macro-Tech 2402 activate transformer thermal protection as long as it is operated within rated conditions (see Section 8, Specifications). One reason is that ODEP keeps the amplifier work- ing under very severe conditions. Even so, higher than rated output levels, excessively low impedance loads and unreasonably high input signals can generate more heat in the trans- former than in the output devices. These condi- tions can overheat the transformer and activate its protection system.
The Macro-Tech 2402 is designed to keep working under conditions where other amplifi- ers would fail. But even when the limits of the amplifier are exceeded, it will still protect itself–and your investment–from damage.
