Page 14
Reference Manual
Macro-Tech
®
24x6 & 36x12 Power Amplifiers
shielded pair cable is another effective way to reduce
or eliminate hum resulting from inductive coupling.
Ground loops often result when two or more devices
are improperly grounded. This causes undesirable
stray currents that may produce hum in the output. The
best way to avoid ground loops is to ensure that all sys-
tem devices are plugged into the same power strip. In
addition, make sure that all cable shields are grounded
at one end only.
Input and output grounds are sometimes tied together
for testing or metering. This can cause
feedback oscil-
lation
from load current in the test loop. In some sys-
tems, even the AC power line may provide this
feedback path. Proper grounding, input isolation and
isolation of common AC devices in the system is good
practice.
3.3.2 Output Connection
Consider the power-handling capacity of your load be-
fore connecting it to the amplifier. Crown is not liable for
damage incurred at any time due to a load being over-
powered. The use of loudspeaker protection fuses is
highly recommended (see Section 3.3.3). Also, please
pay close attention to the Operating Precautions in Sec-
tion 4.1.
HOW TO DETERMINE
APPROPRIATE WIRE GAUGE
It is important to use loudspeaker cables with sufficient
gauge (thickness) for the length being used. The resis-
tance introduced by inadequate loudspeaker cables
will reduce both the output power and the motion con-
trol of the loudspeakers. The latter problem occurs be-
cause the damping factor decreases as the cable
Use Good Connectors
1. To prevent possible short circuits, do not
expose the loudspeaker cable connectors.
2. Do not use connectors that might
accidentally tie two channels together when
making or breaking connections (for example, a
standard three-wire stereo phone plug).
3. Connectors that can be plugged into AC
power receptacles should never be used.
4. Connectors having low current-carrying
capacity should not be used.
5. Connectors with any tendency to short
should never be used.
resistance increases. This is very important because
the amplifier’s excellent damping factor can easily be
negated by insufficient loudspeaker cables.
Use the nomograph in Figure 3.11 and the procedure
that follows to find the recommended wire gauge (AWG
or American Wire Gauge) for your system.
Fig. 3.11 Wire Size Nomograph
40
30
20
15
10
9
8
7
6
5
4
3
2
1
2
5
10
20
50
100
.04
.06
.1
.2
.4
.6
1
2
4
6
10
20
40
8000
Ohms/1000 Feet
(305 Meters)
AWG (American
Wire Gauge)
Feet
Meters
5000
1000
500
100
50
10
5
1
.5
.1
.05
.01
#28
#26
#24
#22
#20
#18
#16
#14
#12
#10
#8
#6
#4
#2
#0
#00
#0000
R
L
Load
Resistance
(Ohms)
R
L
R
S
Damping
Factor
R
S
Source
Resistance
(Ohms)
Two
Conductor
Cable
Copper
Wire
Example Shown:
Load Resistance = 8 ohms
Desired Damping Factor = 500
Source Resistance = 0.016 ohms
Cable Length = 10 feet (3.1 meters)
Recommended Wire: #8 AWG or equivalent
wire with 1.75 ohms or less resistance per
1000 feet (305 meters).
1
0.5
200
500
1,000
2,000
20,000
5,000
10,000
.01
.001
.02
.004
.006
.002
.0004
.0006
.0002
0.3
1.5
0.6
3.1
6.1
15.3
30.5
61.0
152.5
305.0
610.0
1525
1
5
2
10
20
50
100
200
500
1000
2000
5000
.0002
0.6
0.7
0.8
1.5
0.9
