Page 14
Com-Tech Power Amplifiers
Reference Manual
provide enough air flow for even the most extreme con-
ditions. Still, air conditioning can help by reducing the
temperature of the air circulated through the rack. If you
intend to install air conditioning for your amplifiers, you
may want to use Section 7 to determine the hourly ther-
mal dissipation of your system.
3.3 Wiring
Figures 3.4 through 3.7 show common ways to install a
Com-Tech amplifier in a sound system. Input and out-
put terminals are located on the back panel. Please use
care when making connections, selecting signal
sources and controlling the output level. The load you
save may be your own! Crown assumes no liability for
damaged loads resulting from careless amplifier use or
deliberate overpowering.
CAUTION: Always disconnect the AC power and
turn the level controls off when making or breaking
connections.
This is very important when loudspeak-
ers are connected because it reduces the chance of
loud blasts that can cause loudspeaker damage.
3.3.1 Mode of Operation
Proper wiring depends on how you configure your am-
plifier. First, each output channel can be independently
configured to drive step-down transformers in a distrib-
uted “constant voltage” loudspeaker system (70-volt
mode) or loudspeakers that do not have step-down
transformers (8/4-ohm mode). Second, the amplifier
can be configured for Dual, Bridge-Mono or Parallel-
Mono modes. Various combinations of these modes are
possible, so be sure to note any special wiring require-
ments for the mode you will be using.
70
VOLT
8/4
OHM
7 0 V O L T
The 70-volt output mode is used to drive constant volt-
age lines without expensive step-up transformers.
Avoiding the use of step-up transformers not only saves
money, but it also eliminates the distortion and insertion
loss caused by this type of transformer.
Setting up 70-volt mode is easy. Turn off the amplifier,
then slide the recessed output mode switches to the 70
VOLT (right) position.
If required by your system design, Com-Tech
amplifiers
can be configured for either bridge-mono or parallel-
mono modes of operation. To switch your amplifier ac-
cordingly, start by removing power from the unit. Next,
BLOWER
(OPTION 2)
BLOWER
(OPTION 1)
AIR
FLOW
FRONT
OF
RACK
DOOR
AIR
FLOW
EQUIPMENT
RACK
(SIDE VIEW)
Fig. 3.3 Extra Cooling with a Rack-Mounted Blower
because wire tends to cause less air restriction (perfo-
rated panels cause a minimum air restriction of 40%).
A better choice for increasing the air flow behind a rack
cabinet door is to use a “squirrel cage” blower. Mount
the blower at the bottom of the rack so it blows outside
air into the space between the door and the front of the
amplifiers, pressurizing the “chimney” behind the door
(Figure 3.3, Option 1). The blower should not blow air
into or take air out of the space behind the amplifiers.
For racks without a front door, you can evacuate the
rack by mounting the blower at the top of the rack so
that air blows out the back (Figure 3.3, Option 2).
You can estimate the required air flow for a rack by add-
ing together the maximum required air flow ratings of
the individual units. The internal fan in a Com-Tech 210
(if installed), 410 and 810 can move up to 35 cubic feet
(1 cubic meter) of air per minute, while the internal fan
in a Com-Tech 1610 can move up to 65 cubic feet (1.8
cubic meters) per minute. If you mounted one of each
Com-Tech model in a rack, worst-case conditions would
require 170 cubic feet (4.7 cubic meters) of air flow
through the rack every minute (3 x 35 cubic feet + 65
cubic feet = 170 cubic feet).
Air flow restrictions may also result if the air filter be-
comes clogged. If the air supply is unusually dusty, you
can help prevent rapid loading of the unit’s air filter by
pre-filtering the air using commercial furnace filters.
And, when needed, the unit's filter can be cleaned with
mild dish detergent and water (see Section 4.6).
The final method for increased cooling is to use air con-
ditioning. Air conditioning is rarely a necessity because
internal fans and rack-mounted blowers almost always
