Specifications

Operation Manual
Studio Reference I & II Professional Studio Amplifiers
page 18
4.1 Indicators
The front panel has several helpful indicators. The
enable indicator is provided to show the ampli-
fier has been turned on (or enabled) and that its
low-voltage power supply and on-demand forced
air cooling system are working. It does not indicate
the status of the high-voltage power supplies. For
example, the enable indicator will stay on in the
improbable event that one or both channels over-
heat causing an internal shut down of the high volt-
age supplies.
The green ODEP indicators confirm the normal
operation of Crown’s patented Output Device Emu-
lation Protection circuitry. During normal operation,
they glow brightly to confirm the presence of
reserve thermodynamic energy. They dim propor-
tionally as the energy reserve decreases. In the rare
event that there is no reserve, the indicators will turn
off and ODEP will proportionally limit the drive level
of the output stages so the amplifier can continue
safe operation even when the operating conditions
are severe. (For a more detailed description of
ODEP, see Section 4.2.1.)
A channel’s ODEP indicator also turns off if its high-
voltage power supply if it is put in “standby” mode
or the amplifier’s circuit breaker is tripped. The
standby mode is activated if DC or heavy common-
mode current is detected in the output, if the trans-
former thermal protection system is activated, if a
PIP with SmartAmp™ features is used to shut down
a high-voltage supply, or if excessive AC mains
voltage is detected. For more information see Sec-
tion 4.2 and Chapter 6 on Troubleshooting.
4 Advanced Features
and Options
Figure 4.1 Indicators
The yellow IOC indicators act as sensitive distor-
tion meters to provide proof of distortion-free
performance. The IOC (Input/Output Comparator)
circuitry compares the incoming signal’s waveform
to that of the output. Any difference between the two
is distortion. The IOC indicators flash if there is a
difference of 0.05% or more. The IOC indicators
also show input overload by flashing brightly with a
half-second hold delay. It is normal for them to light
momentarily when the amplifier is first turned on.
Note: The channel 2 IOC indicator will stay on in
Parallel-Mono mode. Also, an IOC indicator will
stay on in abnormal situations where a high-voltage
power supply is temporarily put in standby mode.
The green signal presence indicators flash syn-
chronously with the amplifier’s output signal. The
signal detector is connected to the signal path after
the input gain stages and level controls, so a flash-
ing indicator tells you that there is audio in and out
of the amplifier. Note: The signal presence indica-
tors may not report signal presence if the output
signal level is too low.
The dynamic range/level meters are five-seg-
ment output meters that can be set to monitor either
the dynamic range or the level of the output signal.
They are factory-set to show dynamic range. A
switch located behind the front panel is used to
select the meter display mode (see Section 4.4.2 for
complete instructions). As dynamic range meters
they show each channel’s ratio of peak-to-average
power in dB. The dynamic range may be low for
sources like AM/FM radio or low-quality record-
ings. Other sources like live music or high-quality
recordings may be much higher. As output level
meters they show how high the output levels are in
dB relative to full power. At 0 dB, the unit is deliver-
ing full standard 1 kHz power (see Section 7).
4.2 Protection Systems
Studio Reference amplifiers provide extensive pro-
tection and diagnostics capabilities. Protection sys-
tems include ODEP, standby mode, an AC circuit
breaker and transformer thermal protection. These
systems will prevent amplifier damage in virtually
any situation.
4.2.1 ODEP
Crown invented ODEP to solve two long-standing
problems in amplifier design: to prevent amplifier
shutdown during demanding operation and to
increase the efficiency of output circuitry.
To do this, Crown established a rigorous program to
measure the safe operating area (SOA) of each out-
put transistor before installing it in an amplifier.
Next, Crown designed intelligent circuitry to simu-
late the instantaneous operating conditions of the
output transistors. Its name describes what it does:
Output Device Emulation Protection or ODEP. In
addition to simulating the operating conditions of
the output transistors, it also compares their opera-
tion to their known SOA. If ODEP sees that more
power is about to be asked of the output transistors
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.