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Macro-Tech 600/1200/2400 Power Amplifiers

Page 21

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 frequency or DC output. Al-

though it is extremely unlikely that you will ever activate

the amplifier’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 am-

plifier channel in standby mode in rare situations where

heavy common-mode current is detected in the

channel’s output. The amplifier 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 cir-

cuitry is activated in very unusual circumstances where

the unit’s transformer temperature rises to unsafe lev-

els. Under these abnormal conditions, the amplifier will

put the channel of the affected transformer in standby

mode. The amplifier will return to normal operation af-

ter the transformer cools to a safe temperature. (For

more information on transformer thermal protection, re-

fer to the following section.)

4.3.3 Transformer Thermal Protection

All

Macro-Tech

amplifiers have transformer thermal

protection. It protects the power supplies from dam-

age under the rare conditions of transformer tempera-

tures 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 transformer cools to a safe temperature.

It is extremely unlikely that you will ever see a

Macro-Tech

amplifier activate transformer thermal pro-

tection as long as it is operated within rated conditions

(see Section 6,

Specifications

). One reason is that

ODEP

keeps the amplifier working 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 conditions

can overheat the transformer and activate its protec-

tion system.

Macro-Tech

amplifiers are designed to keep working

under conditions where other amplifiers would fail. But

even when the limits of a

Macro-Tech

amplifier are ex-

ceeded, it will still protect itself—and your investment—

from damage.

4.3 Protection Systems

Macro-Tech

amplifiers provide extensive protection

and diagnostics capabilities. Protection systems in-

clude

ODEP

, “standby” mode, fuses (or breakers), and

special thermal protection for the unit’s transformers.

4.3.1

ODEP

Crown invented

ODEP

to solve two long-standing prob-

lems in amplifier design: to prevent amplifier shutdown

during demanding operation and to increase the effi-

ciency of the output circuitry.

To do this, Crown established a rigorous program 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 instanta-

neous operating conditions of those output transistors.

Its name describes what it does: Output Device Emu-

lation Protection or

ODEP

. In addition to simulating the

operating conditions of the output 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 capable 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 out-

put efficiency to never-before-achieved levels while

greatly increasing amplifier reliability.

The on-board intelligence is monitored in two ways.

First, the front panel

ODEP

indicators show whether

the amplifier is functioning correctly or if

ODEP

is limit-

ing the drive level. Second,

ODEP

data is fed to the

back panel

P.I.P.

connector so advanced

P.I.P.

mod-

ules like the IQ-P.I.P. 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.

4.3.2 Standby Mode

At the heart of the protection systems is the standby

mode which removes power from the high-voltage sup-

plies to protect the amplifier and connected loads. The

standby mode can be identified using the indicator

table in Figure 4.2.

Standby mode can be activated in several situations.

First, if dangerous subsonic frequencies or direct cur-

rent (DC) is detected in the amplifier’s output, the unit

will activate its DC/low-frequency protection circuitry

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