5
Operating Manual - Powerflex Multi-Channel Power Amplifier
3.3
AC Grounding Requirements
To reduce the risk of ground loop hum, all system
ground references should originate at the same point in
your AC power distribution. Do not remove the amplifier’s
ground pin, as it creates a potential shock hazard.
4.
CABLE REQUIREMENTS
4.1
Input Cables
Be sure to use shielded cable whether balanced or
unbalanced. Shielding which is properly grounded will
protect the signal from outside electrical interference such
as RF, fluorescent lighting, and computer/display emis-
sions. As a general rule, unbalanced or single-ended (tip-
sleeve) lines of less than 10 feet are satisfactory, but greater
distances or noisy field environments require a balanced
signal. Avoid running input lines in close proximity or
parallel to long speaker lines, AC power cables, or power
transformers, as this may generate hum or oscillation.
4.2
Output Cables
Powerflex amplifiers are capable of delivering
high levels of output current, therefore the wire gauge used
for speaker cables is particularly important. Inadequate
wire gauge can add significant resistance to the speaker’s
own impedance, especially over long distances, reducing
the power which is actually delivered to the speaker. It
could also result in a decreased damping factor and pos-
sible fire hazard. Since power at the speaker load is of
primary concern in system design, we have included a table
to best determine appropriate wire gauge for your appli-
cation. The following table lists the resistance per 100
feet of common copper wire gauges, and also gives the
percentage of the speaker load power which would be lost
in an arbitrary 100 ft run of different gauges of 2-conduc-
tor copper speaker wire.
Wire Gauge
Ω
/100ft
8
Ω
load
4
Ω
load
#8
.0605
Ω
0.8%
1.5%
#10
.1018
Ω
1.3%
2.5%
#12
.1619
Ω
2.0%
4.0%
#14
.2575
Ω
3.2%
6.4%
#16
.4094
Ω
5.1%
10.2%
#18
.6510
Ω
8.1%
16.3%
Table 4.1: Wire gauge resistance/power loss
This table expresses the power loss as a percent-
age of the load’s power rather than the total amplifier out-
put power in order to accurately determine power loss at
other cable lengths. For example, if you plan to deliver
150 watts to an 8
Ω
load through 50 ft of 14 ga. cable, the
power loss in the cable would be half that of a 100 ft run
of #14 wire as shown in the table, or 1.6% of 150W, which
is an insignificant 2.4 watts. However, if you were to run
200 ft of 18 ga. cable to a 4
Ω
load, the loss would be twice
that of the 100 ft run shown in the table, or 32.6% of 250W,
which is 81.5 watts lost as heat. Always be sure to use
adequate gauge speaker wire.
5.
RACK-MOUNTING REQUIREMENTS
5.1
Mechanical
Powerflex amplifiers are designed to fit in stan-
dard 19-inch equipment racks. The front panel rack-mount
ears are sufficiently strong for most applications, however
if you desire further integrity for mobile racks, we recom-
mend using the four additional holes in the back of the
chassis for supplemental rear-mounting (see dimensional
drawing for details).
5.2
Cooling
Be certain that both the front and back of the rack
have unhindered access to free air flow. Fan direction is
from front to back. It is not necessary to leave empty space
above or below.
5.3
Grounding
In some installations where the sound system is
sensitive to RF noise or system-induced oscillation, it may
be necessary to ground the amplifier’s chassis to the rack
enc losur e. T his is accomplished using star type
lockwashers on the four rack mounting screws. These star
washers will penetrate through the amplifier’s paint to ad-
equately ground the chassis to the rack.
