Output Connection; Wire Size Nomograph - Crown Macro-Tech MA-1200 Reference Manual

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.

3.3.5 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 overpowering. Fus-
ing loudspeaker lines is highly recommended (see Sec-
tion 3.3.6). Also, please pay close attention to the
precautions provided in Section 4.1.
Use Good Connectors
1. To prevent possible shorts, do not expose
the loudspeaker cable connectors.
2. Do not use connectors that might acciden-
tally tie two channels together when making or
breaking connections (for example, a stan-
dard three-wire stereo phone plug).
3. Connectors that can be plugged into AC
power receptacles should never be used.
4. Connectors with low current-carrying ca-
pacity should not be used.
5. Connectors with any tendency to short
should never be used.
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
Page 16
Macro-Tech 600/1200/2400 Power Amplifiers
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 3.13 and the procedure
that follows to find the recommended wire gauge (AWG
or American Wire Gauge) for your system.
R
L
R
S
DAMPING
FACTOR
20,000
10,000
5,000
2,000
R
L
1,000
40
LOAD
RESISTANCE
500
(ohms)
30
200
100
20
50
20
15
10
5
10
9
2
8
1
7
6
5
4
3
Example Shown:
R = 8 ohms; R
L
Cable Length = 10 ft.; answer: #8 wire
2
1.5
1
0.9
0.8
0.7
0.6
0.5
Fig. 3.13 Wire Size Nomograph
.0002 R
S
SOURCE
RESISTANCE
(ohms)
.0004
.0006
.001
.002
.004
.006
.01
.02
COPPER
8000
.04
WIRE
5000
(AWG)
.06
(ohms/1000 ft.)
.1
1000
2-COND.
CABLE
500
(feet)
.2
1
2
#28
100
5
#26
.4
50 #24
10
.6 #22
20
#20
50
1 #18
100
10
#16
200
#14
5
500
#12
2
1000
#10
2000
#8
1
#6
4
5000
#4
.5
#2
6
#0
#00
10
.1
#0000
.05
20
.01
40
= 0.016 ohms or D.F. = 500;
S
Reference Manual