Here are the equations used to calculate the data presented in Figure 1:
The quiescent power draw is a maximum value and includes power drawn by the fan. The
following equation converts power draw in watts to current draw in amperes:
The value used for Power Factor is 0.83. The Power Factor variable is needed to compen-
sate for the differnece in phase between the AC mains voltage and current. The following
equation is used to calculate thermal dissipation:
The value used for inefficiency is 1.00-efficiency. The factor 3.415 converts watts to btu/
hr. Thermal dissipation in btu is divided by the constant 3.968 to get kcal. If you plan to
measure output power under real-world conditions, the following equation may also be
helpful:
AC Power Draw and Thermal Dissipation
The information provided on this page is calculated data based on driv-
ing both channels to rated output using the 1 kHz Maximum Average
Power rating method.
Other parameters used in calculation include a conservative idle current
estimate of 90 watts and a conservative estimate of effeciency at 65%.
Information is provided only for getting an idea of current draw and heat
produced. Actual performance will vary depending on environment, pro-
gram material, load, signal, and AC mains voltage and frequency.
Values of calculated current draw are intended to represent average draw
corresponding to the thermal breaker requriements that should be met to
handle the amplifier as a load on the AC mains.
Peak current draw with dynamic program material may be significantly
higher. Thermal information is provided to assist with calculating air
conditioning needs. The data here should not be construed as specifica-
tions.
Duty cycle of various program material:
Individual speech: 10%
Acoustic/chamber music: 20%
Full-range rock music: 30%
Compressed rock music: 40%
Pink noise: 50%
Total measured output power
from all channels (watts)
Thermal
Dissipation
(btu/hr)
=
+
Quiescent Power
Draw (watts)
.35
x
Amplifier Efficienc
(.65)
x
3.415
Current Draw
(amperes)
=
AC Mains Power
Draw (watts)
x
AC Mains
Volta
e
Power
Factor
.83
AC Mains Power
Draw (watts)
=
Total output power with all
channels driven (watts)
x
Duty
Cycle
Amplifier Efficiency (.65)
+
Quiescent Power
Draw (watts)
Total output power with all
channels driven (watts)
Thermal
Dissipation
(btu/hr)
=
+
Quiescent Power
Draw (watts)
x
Duty
Cycle
Amplifier Efficiency (.65)
x
3.415
.35
x
SR-II
S T U D I O R E F E R E N C E S E R I ES
A Harman International Company
Crown International, Inc.
1718 W. Mishawaka Rd.
Elkhart, IN 46517-9439
TEL: 574-294-8200
FAX: 574-294-8FAX
www.crownaudio.com
For more details refer to the applicable Operation
Manual or contact Crown Factory Service. The
provided data should not be construed as specif-
ciations.
Crown and Crown Audio® are registered trade-
marks of Cown international, Inc. Printed in
U.S.A.
©2005 Crown Audio, Inc.
04/05 138355-1
LOAD
2 Ohm Stereo / 4 Ohm Bridge 4 Ohm Stereo / 8 Ohm Bridge / 2 Ohm Parallel Mono 8 Ohm stereo / 16 Ohm Bridge / 4 Ohm Parallel Mono
AC
Mains
Power
Draw
(watts)
Current Draw
(Amps)
Thermal
Dissipation
AC
Mains
Power
Draw
(watts)
Current Draw
(Amps)
Thermal
Dissipation
AC
Mains
Power
Draw
(watts)
Current Draw
(Amps)
Thermal
Dissipation
Duty
Cycle
120V 230V btu/hr kcal/hr 120V 230V btu/hr kcal/hr 120V 230V btu/hr kcal/hr
50% 944 9.8 4.9 1360 343 636 6.5 4.9 970 244
40% 773 8.0 4.0 1150 290 527 5.4 4.0 840 212
30% 602 6.2 3.1 940 237 418 4.3 3.1 705 178
20% 432 4.5 2.2 730 184 308 3.2 2.2 575 145
10% 261 2.7 1.4 520 131 199 2.1 1.4 440 111
Studio Reference II
(44 pages)
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