70V Distribution Systems - Mackie M1200/M1400 Owner's Manual

The thickness of wire is rated in gauges.
Use the chart below to determine the correct
gauge of wire to use according to the distance
between the speakers and the amplifier, and
the impedance of the load the amplifier is driv-
ing. This ensures that the power lost across the
speaker wire is less than 0.5 dB.
Load
Wire Length Impedance
Up to 25 ft. 2
4
8
Up to 40 ft. 2
4
8
Up to 60 ft. 2
4
8
Up to 100 ft. 2
4
8
Up to 150 ft. 2
4
8
Up to 250 ft. 2
4
8

70V DISTRIBUTION SYSTEMS

A distributed sound system uses a constant-
voltage, high-impedance network that feeds a
number of tapped transformers which, in turn,
deliver power to individual speakers. Each tap
is rated in watts, so you can select the amount
of power delivered to the speaker. Developed
for distributed paging and public address sys-
tems, one benefit of such a system is that it
eliminates complicated impedance calcula-
FR SERIES
POWER AMPLIFIER
IN BRIDGE MODE RC NETWORK
C1 C2
+
+
CH 1
–
R1
–
CH 2
+
RC NETWORK VALUES
C1 = C2 = 660 F @ 250VDC
R1 = 4 @ 100W
ALTERNATE RC NETWORK
Note: You can substitute
a single capacitor for C1/C2.
C3 = 330 F @ 250VDC,
NON-POLARIZED.
70V Constant Voltage
Distribution System
tions when setting up a multi-speaker system.
You just add up the total wattages of all the
speakers in the system and make sure that it
doesn't exceed the total power rating of the
amplifier (allowing at least 10% for insertion
losses). Another benefit is that by using high
voltage and low current, losses in the speaker
distribution wiring are kept to a minimum.
Standard voltage levels include 25V, 70V, and
Gauge of
100V, but 70V systems are most commonly used
Wire
in commercial sound distribution systems in
14 gauge
the U.S.
16 gauge
18 gauge
M•1200/M•1400 amplifiers, they can be used
12 gauge
to directly drive 70V constant-voltage distribu-
14 gauge
tion systems without the use of a step-up
18 gauge
transformer. When the M•1200 amplifier is
10 gauge
operated in BRIDGE
12 gauge
800 watts into 8 ohms, or 80V. This is slightly
16 gauge
higher than the standard 70.7V for which the
8 gauge
system was designed. You can recalculate the
10 gauge
actual power delivered to each tap by multiply-
14 gauge
ing the tap's rated wattage by a correction
6 gauge
factor (K). The correction factor is P
8 gauge
where P
12 gauge
into 8 ohms (BRIDGE mode), and P
4 gauge
power delivered by 70.7V into 8 ohms (625W).
6 gauge
10 gauge
2.5W tap becomes 3.2W, a 5W tap becomes
6.4W and a 10W tap becomes 12.8W.
2.5W tap becomes 3.3W, a 5W tap becomes
6.6W and a 10 W tap becomes 13.2W.
ers is that they saturate at very low frequencies,
which causes their impedance to decrease, ap-
proaching the DC resistance of the copper wire.
This can result in overloading the amplifier if
the signal contains lots of low frequencies.
When using an FR Series amplifier in a 70V dis-
tribution system, set the LOW CUT FILTER
to 100Hz or higher. In addition, install an RC
network at the SPEAKER OUTPUT
amplifier, as shown in the figure below.
+
C3
R1
+
–
Because of the high power capability of the
mode, it can produce
is the power delivered by the amplifier
1
M•1200: K = 800W/625W = 1.28. Thus, a
M•1400: K = 850W/625W = 1.32. Thus, a
CAUTION: A characteristic of tapped transform-
+
–
/P ,
1 2
is the
2
of the
70V LINE
CONSTANT
VOLTAGE
TRANSFORMER
POWER TAP
SWITCH
+
–
25