Page 22
Com-Tech Power Amplifiers
Reference Manual
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 3.3.5). Also, please pay close attention to Section
4.1,
Precautions.
You should always install loudspeaker cables of suffi-
cient gauge (wire thickness) for the length used. The
resistance introduced by inadequate output cables will
reduce the amplifier’s power to and motion control of
the loudspeakers. The latter problem occurs because
the damping factor decreases as the cable resistance
increases. This is very important because the amplifier’s
excellent damping factor can be easily negated by us-
ing insufficient cable.
Use the nomograph in Figure 3.14 and the following
procedure to find the recommended wire gauge (AWG
or American Wire Gauge) for your system.
1. Note the load resistance of the loudspeakers con-
nected to each channel of the amplifier. If you are using
70-volt output, be sure to determine the load resis-
tance of the step-down transformers (Crown’s constant
voltage computer can help with this, see Section 8.3).
Mark this value on the
Load Resistance
line of the no-
mograph.
2. Select an acceptable damping factor and mark it on
the
Damping Factor
line. Your amplifier can provide
an excellent damping factor of 1,000 from 10 to 400 Hz
in Stereo mode with an 8-ohm load. In contrast, typical
damping factors are 50 or lower. Higher damping fac-
tors yield lower distortion and greater motion control
over the loudspeakers. A common damping factor for
commercial applications is between 50 and 100.
Higher damping factors may be desirable for live
sound, but long cable lengths often limit the highest
damping factor that can be achieved practically. (Un-
der these circumstances, Crown’s
IQ System is often
used so amplifiers can be easily monitored and con-
trolled when they are located very near the loudspeak-
ers.) In recording studios and home hi-fi, a damping
factor of 500 or more is desirable.
3. Draw a line through the two points with a pencil, and
continue until it intersects the
Source Resistance
line.
4. On the
2-Cond. Cable
line, mark the length of the
cable run.
5. Draw a pencil line from the mark on the
Source Resis-
tance
line through the mark on the
2-Cond. Cable
line,
and on to intersect the
Annealed Copper Wire
line.
6. The required wire gauge for the selected wire length
and damping factor is the value on the
Annealed Cop-
per Wire
line.
Note: Wire size increases as the AWG
gets smaller.
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
5
10
20
50
1
2
100
200
500
1000
2000
5000
8000
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
LOAD
RESISTANCE
(ohms)
L
R
R
DAMPING
FACTOR
L
S
R
SOURCE
RESISTANCE
(ohms)
S
2-COND.
CABLE
(feet)
ANNEALED
COPPER
WIRE
(AWG)
(ohms/1000 ft.)
Example Shown:
R = 8 ohms; R = 0.016 ohms or D.F. = 500;
Cable Length = 10 ft.; answer: #8 wire
L
S
1
0.5
200
500
1,000
2,000
20,000
5,000
10,000
.01
.001
.02
.004
.006
.002
.0004
.0006
.0002
0.6
0.7
0.8
1.5
0.9
Fig. 3.14 Wire Size Nomograph
