Crown ma-1200 Guida Di Riferimento

This section provides detailed information about the
amount of power and current drawn from the AC mains
by the Macro-Tech

 600, 1200 and 2400 amplifiers and

the amount of heat produced under various conditions.
The calculations presented here are intended to pro-
vide a realistic and reliable depiction of the amplifiers.
The following assumptions or approximations were
made:

• The amplifier’s available channels are loaded and full

power is being delivered.

• The amplifier efficiency at standard 1-kHz power is

estimated to be 65%.

• Quiescent power draw is 90 watts (an almost negli-

gible amount for full-power calculations).

• Quiescent thermal dissipation equals 105 btu/hr at

90 watts.

• The estimated duty cycles take into account the typi-

cal crest factor for each type of source material.

• Duty cycle of pink noise is 50%.

• Duty cycle of highly compressed rock ‘n’ roll mid-

range is 40%.

• Duty cycle of rock ‘n’ roll is 30%.

• Duty cycle of background music is 20%.

• Duty cycle of continuous speech is 10%.

• Duty cycle of infrequent, short duration paging is 1%.

Here are the equations used to calculate the data pre-
sented in Figures 7.1 through 7.3:

AC Mains Power

Draw (watts)

=

Total output power with all

channels driven (watts)

x Duty

Cycle

Amplifier Efficiency (.65)

+ Quiescent Power

Draw (watts)

The quiescent power draw of 90 watts is a maximum
value and includes power drawn by the fan. The follow-
ing equation converts power draw in watts to current
draw in amperes:

Current Draw

(amperes)

=

AC Mains Power

Draw (watts)

x

AC Mains

Voltage

Power

Factor (.83)

The power factor of 0.83 is needed to compensate for
the difference in phase between the AC mains voltage
and current. The following equation is used to calculate
thermal dissipation:

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

The constant 0.35 is inefficiency (1.00–0.65) and the
factor 3.415 converts watts to btu/hr. Thermal dissipa-
tion 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:

Total measured output power

from all channels (watts)

Thermal

Dissipation

(btu/hr)

=

+

Quiescent Power

Draw (watts)

.35

x

Amplifier Efficiency (.65)

(

)

x 3.415

Fig. 7.1  Macro-Tech 600 Power Draw, Current Draw and

Thermal Dissipation at Various Duty Cycles