Crown Micro-Tech 1201 Informations techniques télécharger pdf (Page 20)

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Micro-Tech 600/1200/2400 Power Amplifiers

Reference Manual

of delivering under the present conditions,

ODEP

immedi-

ately 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. Un-

der normal conditions, no limiting is required and

ODEP

transparent to the audio signal.

This level of protection enables Crown to increase out-

put efficiency to never-before-achieved levels while

greatly increasing reliability. As described in the previ-

ous section, the on-board intelligence is monitored by

the front panel

ODEP

indicators that show whether the

amplifier is functioning correctly or if

ODEP

is limiting

the drive level.

With

ODEP

you get maximum power with maximum pro-

tection so the show goes on.

4.3.2 Ultrasonic and Radio Frequency Protection

Micro-Tech

amplifiers have a controlled slew rate. This

means that their design limits the frequencies they can

reproduce. At the same time, the amplifier’s controlled

slew rate has no effect on its audio performance be-

cause limiting occurs well above 20 kHz. This approach

protects the amplifier from radio frequencies, and also

protects some sensitive loads (like tweeters). In the real

world, an amplifier’s slew rate only needs to be large

enough to deliver the maximum voltage at the highest

required frequency—higher slew rates actually allow the

reproduction of undesirable frequencies.

4.3.3 Drive Protection

The drive protection system temporarily removes drive

from the output stages to protect the amplifier and its

connected loads. Drive protection can be activated in

two situations. First, if dangerous subsonic frequencies

or direct current (DC) is detected in the amplifier’s out-

put, the unit will activate its DC/low-frequency protec-

tion circuitry which puts the affected channel in drive

protection mode. This protects the loads and prevents

oscillation. The amplifier resumes normal operation

when it no longer detects dangerous output. Although it

is extremely unlikely that you will ever activate the

amplifier’s DC/low-frequency protection system, im-

proper source materials like subsonic square waves or

a severely clipped signal can activate this system.

The amplifier’s fault protection system puts the affected

channel into drive protection mode in rare situations

where heavy common-mode current is detected in its

output. The amplifier should never output heavy com-

mon-mode current unless its circuitry is damaged. Acti-

vating drive protection helps prevent further damage.

4.3.4 Transformer Thermal Protection

All

Micro-Tech

amplifiers have transformer thermal pro-

tection. The amplifier’s transformer thermal protection

circuitry is activated in very unusual circumstances

where the unit’s transformer temperature rises to unsafe

levels. Under these abnormal conditions, the amplifier

will remove power from the affected channel’s high-volt-

age power supply which puts the channel in drive pro-

tection mode. The amplifier channel will return to normal

operation after its transformer cools to a safe tempera-

ture.

It is extremely unlikely that you will ever see a

Micro-Tech

amplifier activate transformer thermal protection as long as

it is operated within rated conditions (see Section 6,

Speci-

fications

). 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 transformer than in the output devices. These condi-

tions can overheat a transformer and activate its protection

system.

Micro-Tech

amplifiers are designed to keep working un-

der conditions where other amplifiers would fail. But

even when a

Micro-Tech’s

limits are exceeded, it will still

protect itself—and your investment—from damage.

4.3.5 Fuses and Circuit Breakers

120 VAC, 60 Hz models and all

Micro-Tech 2400s

have

an internal fuse that protects the low-voltage power sup-

ply and cooling fan. The high-voltage power supplies

for the

Micro-Tech 600

and

1200

are protected by internal

fuses, while the power supplies for the

Micro-Tech 2400

high-voltage supplies are protected by circuit breakers.

With rated loads and output levels, the fuses (or circuit

breakers) should only shut down the amplifier in the rare

instance of a catastrophic failure.

ODEP

protection

keeps the amplifier operational under most other severe

conditions. The fuses (or circuit breakers) can also shut

down the amplifier in cases where extremely low-imped-

ance loads and high output levels result in current draw

that exceeds their rating. Again, this should only be pos-

sible when operating

outside rated conditions

like when

the amplifier is used to drive a 1 ohm load in Stereo

mode, or when an input signal is clipped severely.

Micro-Tech

amplifiers do not blow their fuses or trip their

breakers unless something is wrong. In the rare event

that an internal fuse blows, please refer the unit to a

qualified technician. If a breaker in a

Micro-Tech 2400

trips, try to identify and correct the problem before re-

setting the breakers. If the problem persists, refer the

unit to a qualified technician.

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