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Com-Tech Power Amplifiers
Reference Manual
4 Operation
4.1 Precautions
Com-Tech amplifiers are protected from internal and ex-
ternal faults, but you should still take the following pre-
cautions for optimum performance and safety:
1. Improper wiring for the Dual, Bridge-Mono and Parallel-
Mono modes, as well as the 8/4-ohm and 70-volt output
modes can result in serious operating difficulties. Refer
Section 3.3.1 for details.
2. WARNING: Never operate the amplifier in Bridge-
Mono or Parallel-Mono mode unless both outputs
are configured the same (8/4-ohm or 70-volt).
3. When driving an inductive load (like a 70-volt step-
down transformer) use a high-pass filter or protective
network to prevent premature activation of the
amplifier’s protection circuitry (see Section 3.3.3).
4. WARNING: Do not change the position of the dual/
mono switch or the output mode switches unless
the amplifier is first turned off.
5. CAUTION: In Parallel-Mono mode, a jumper must be
installed between the Channel 1 and 2 positive (+)
output terminals. Be sure to remove this jumper for
Dual or Bridge-Mono modes, otherwise high distor-
tion and excessive heating will occur.
Check the
dual/mono switch on the back panel for proper position.
6. Turn off the amplifier and unplug it from the AC
power before removing a PIP module or before re-
moving the dust filter.
7. Use care when making connections, selecting signal
sources and controlling the output level. The load you
save may be your own!
8. Do not connect input and output ground leads together.
Ground loops and oscillations may result.
9. Operate the amplifier from AC mains of not more than
10% above or below the selected line voltage and only
the specified line frequency.
10. Never connect the output to a power supply output,
battery or power main.
Electrical shock may result.
11. Tampering with the circuitry by unqualified personnel, or
making unauthorized circuit changes may be hazard-
ous and invalidates all agency listings.
Remember: Crown is not liable for damage that results
from overdriving other system components.
4.2 Indicators
The front panel of a Com-Tech amplifier has several
helpful indicators. The amber
Enable indicator
shows
that the amplifier has been turned on (or enabled). It will
dim when the unit goes into energy-saving mode. When
the Enable indicator is lit, the low-voltage power supply
is working. It does not indicate the status of the high-
voltage power supplies. For example, the Enable indi-
cator will remain lit in the unlikely event that one of the
amplifier’s protection systems (described in Sec-
tion 4.3) puts the channel in “standby” mode. The En-
able indicator will stay on for all conditions shown in
Figure 4.2 except for the first example, “There is no
power to the amplifier.”
The green
ODEP indicators
confirm the normal opera-
tion of Crown’s patented Output Device Emulation Pro-
tection circuitry. During normal operation, they glow
brightly to confirm the presence of reserve thermal-dy-
namic energy. They dim proportionally as the energy
reserve decreases. In the rare event that there is no re-
serve, they will turn off and ODEP will proportionally limit
the drive level of the output stages so the amplifier can
continue safe operation even when conditions are se-
vere. (See Section 4.3.1 also.)
An ODEP
indicator also turns off if the channel goes into
“standby” mode or the amplifier’s circuit breaker is tripped.
The standby mode is activated if DC or heavy common-
mode current is detected at the output, if the transformer
thermal protection system is activated, or if a PIP such as
the
IQ-PIP-USP2 is used to put the channel into standby.
(See Section 4.3.3 and Figure 4.2.)
The yellow
IOC indicators
act as sensitive distortion
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.
It is normal for them to light momentarily when the am-
plifier is first turned on.*
The green
Signal Presence Indicators
(SPI) flash syn-
chronously with the output audio. The SPI detector cir-
cuit is connected to the amplifier output, so a flashing
indicator tells you that there is audio in and out of the
amplifier.
Note: The SPI’s may not report signal pres-
ence if the output signal level is below 34 mV.
Fig. 4.1 Indicators
_______________________
* Note: When the amplifier’s dual/mono switch is moved to the Parallel/
Mono position, the Channel 2 IOC indicator will illuminate. This is a nor-
mal condition in this configuration.
