Page 13
Com-Tech Power Amplifiers
Reference Manual
information in Section 7 to estimate the amplifier’s ther-
mal dissipation for your application. In general, a North
American Com-Tech 210 that dissipates more than 410
btu (110 kcal) per hour per unit will need additional cool-
ing. If you are not sure, observe the ODEP indicators
while the amplifier is operating under worst-case condi-
tions. If the indicators dim, additional cooling is recom-
mended.
There are at least three ways to provide extra cooling
for an amplifier that does not have an internal fan. The
most effective method is to install an internal fan which
is available from Crown as an accessory (refer to sub-
section 8.3). A cooling fan (part GCT200FAN) kit is
available for North American Com-Tech 210s (all other
units include a fan). Crown recommends the kit if you
will be operating the amplifier at high levels or in high
temperatures for long periods. Refer to paragraph 8.3
for more information on the cooling fan kit
A rack-mounted blower or an air conditioner can also
be used to provide extra cooling. In some situations,
you may find it practical to use these methods without
installing a fan in each amplifier. However, we generally
recommend that you use the internal fans because they
provide the most efficient cooling, and are active only
when needed. Amplifiers that already have internal fans
can also take advantage of a rack-mounted blower or
air conditioner, so these approaches will be discussed
in the section that follows.
3.2.2 Additional Cooling for Units with Internal Fans
If multiple amplifiers will be operated under demanding
conditions (such as driving loads less than 4 ohms), or
if air flow through the rack will be restricted, you should
verify that the total air flow through the rack will be suffi-
cient. As described in Section 3.2.1, sufficient air flow
can be tested in the real world by observing the ODEP
indicators while operating under worst-case conditions.
If the indicators dim, cooling can be improved by re-
ducing air restrictions, installing a rack-mounted blower,
or using an air conditioner.
Many things can cause air flow restrictions, including
improper mounting, bunched up power cords, closed
rack doors, and clogged dust filters. A Com-Tech am-
plifier should be mounted in a way that allows sufficient
air flow into the front intakes, out the side exhaust vents,
and out the back of the rack. If your rack has a front
door, it is usually best to leave it open and avoid block-
ing the air intakes. If this is impossible, supplement the
air flow by mounting a grille in the door or with a rack-
mounted blower. If you install a grille in the door, we
recommend wire grilles instead of perforated panels,
AIR
FLOW
AIR FLOW
RACK
CABINET
16 in
40.6 cm
2 in
(5 cm)
MIN.
17 in
43.2 cm
AIR
FLOW
AMPLIFIER
(TOP VIEW)
IMPORTANT: Be sure the back of
the amplifier is supported.
Fig. 3.2 Top View of a Rack-Mounted Unit
The air flow requirement for a Com-Tech amplifier de-
pends on many things, but the most important factor is
average output power. Air flow requirements increase
as output power increases, so anything that affects out-
put power also affects the required air flow.
Average output power is mainly affected by three
things: (1) duty cycle of the input signal, (2) load im-
pedance, and (3) rated output power. First, as the duty
cycle of the input signal increases, the average output
power level increases. For example, the amplifier will
need more air flow with a rock ‘n’ roll input signal than
with infrequent paging. Second, as the load impedance
of a connected loudspeaker gets smaller, more current
will flow through the load which effectively increases
output power. This means you can expect the amplifier
to require more air flow with a 4-ohm load than with an
8-ohm load. Finally, an amplifier that is rated for higher
power output is usually used at higher average output
levels. So a Com-Tech 1610 delivering full output will
require more air flow than a Com-Tech 210. These rela-
tionships and the resulting thermal dissipation levels are
defined mathematically in Section 7.
3.2.1 Cooling for Units without Internal Fans
All units have a continuously variable on-demand cool-
ing fan except for the North American Com-Tech 210.
Forced-air cooling may not be needed for applications
with a low duty cycle such as paging or background
music. This is why the North American Com-Tech 210 is
usually provided without a fan.
If you will be using a North American Com-Tech 210 in a
high-temperature environment, or at full power for sus-
tained periods, you can anticipate that additional cool-
ing will be needed. It may also be helpful to use the
