Power-Tech Series Power Amplifiers
Page 9
Reference Manual
3 Operation
3.1 Precautions
Although your amplifier is protected from external faults,
the following safety precautions are recommended:
1.
There are important differences among the Stereo,
Bridge-Mono and Parallel-Mono operating modes.
Please refer to Section 2 for additional information.
2.
WARNING: Do not change the position of the
stereo/mono switch unless the amplifier is first
turned off.
3.
CAUTION: In Parallel-Mono mode, a jumper is
used to connect the red binding post outputs.
Be sure to remove this jumper for Bridge-Mono
or Stereo mode, or high distortion and exces-
sive heating will occur.
Also, make sure the ste-
reo/mono switch is set to the proper position.
4.
Use care when making connections, selecting sig-
nal sources and controlling the output level. The
load you save may be your own!
5.
Do not short the ground lead of an output cable to
the input signal ground. This will form a ground
loop and may cause oscillations.
6.
Operate the amplifier from AC mains of not more
than 10% variation above or below the selected
line voltage and only the specified line frequency.
7.
Never connect the output to a power supply
output, battery or power main.
Such connec-
tions may result in electrical shock.
8.
Tampering with the circuitry by unqualified person-
nel or making unauthorized circuit changes may
be hazardous and invalidates all agency listings.
Remember: Crown is not liable for any damage that
results from overdriving other system components.
3.2 Indicators
When lit, the amber
enable
indicator shows that the
amplifier has been turned on. It is driven only by the low-
voltage power supply and does not indicate the status of
the high-voltage supplies.
The
signal/
IOC
indicators flash green in sync with the
audio input signal, and flash yellow if the input waveform
differs from the output by more than 0.05%.
IOC reports
any distortion over 0.05% introduced by the amplifier
including harmonic distortion, intermodulation distortion
and clipping distortion.
3.3 Protection Systems
Power-Tech amplifiers have extensive protection
systems, including
ODEP, ultrasonic/RF protection, drive
protection, transformer thermal protection and fuses or
circuit breakers to protect the power supplies.
3.3.1
ODEP
Crown invented
ODEP to keep the amplifier working
under demanding conditions and to increase output
efficiency. To do this, Crown established a rigorous
program to measure each transistor’s
safe operating
area (SOA). Intelligent circuitry was then designed to
simulate the instantaneous conditions of the output
transistors. Its name describes what it does: Output
Device Emulation Protection, or
ODEP. In simple terms,
ODEP compares transistor conditions to their known
SOA. If more power will be asked of them than they can
deliver under the existing conditions,
ODEP limits the
drive until conditions fall within the SOA. Limiting is
proportional and kept to an absolute minimum—only
what is required to prevent output transistor damage.
Under normal conditions, no limiting is required and
ODEP is transparent to the audio signal.
ODEP makes possible a quantum leap in output
efficiency and reliability—with
ODEP, the show goes on.
3.3.2 Ultrasonic and Radio Frequency Protection
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 undesirable
ultrasonic and radio frequencies to be reproduced. By
design,
Power-Tech amplifiers have a controlled slew
rate to limit the highest frequencies that they reproduce.
Limiting occurs well above 20 kHz, so there is no audible
affect on performance. This approach protects the
amplifier from radio frequencies and can even protect
some sensitive loads (including some tweeters).
3.3.3 Drive Protection
The drive protection system temporarily removes output
drive to protect the amplifier and its loads. Drive
protection can be activated in two situations. First, if
dangerous subsonic frequencies or direct current (DC)
is detected in the amplifier’s output, the unit will activate
its DC/low-frequency protection circuitry which puts the
amplifier in drive protection mode. This protects the
loads and prevents oscillations. The unit resumes normal
operation as soon as the amplifier no longer detects
dangerous output. Although it is extremely unlikely that
you will ever activate the amplifier’s DC/low-frequency
protection system, improper source materials like
subsonic square waves or input overloads that
excessively clip the input signal can activate this system.
