Crown Audio Xs Series operation manual AC Power Draw and Thermal Dissipation

Xs Series Power Amplifiers

7 AC Power Draw and Thermal Dissipation

This section provides detailed information about the amount of power and current drawn from the AC mains by Xs Series amplifiers and the amount of heat produced under various conditions. The calculations presented here are intended to provide 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.

•Efficiency at standard 1 kHz power into 4 ohms is 61% for the Xs500, 61.3% for the Xs700, 54.0% for the Xs900 and 54.0% for the Xs1200.

•Quiescent power draw is 36 watts for the Xs500, 36 watts for the Xs700, 37.4 watts for the Xs900 and 37.4 watts for the Xs1200 (an almost negligible amount for full-power calculations).

•The estimated duty cycles take into account the typical crest factor for each type of source material.

•Duty cycle of pink noise is 50%.

•Duty cycle of highly compressed rock ‘n’ roll midrange 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 presented in Figures 7.1, 7.2, 7.3, and 7.4.

		Total output power with all	x	Duty
AC Mains Power	=	channels driven (watts)		Cycle	+	Quiescent Power
Draw (watts)		Amplifier Efficiency (.65)				Draw (watts)

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:

			AC Mains Power
Current Draw	=		Draw (watts)
(amperes)		AC Mains x		Power
			Voltage	Factor (.83)

The value used for Power Factor is 0.83. The Power Factor variable 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:

Thermal		Total output power with all	x	Duty	x .35		Quiescent Power
		channels driven (watts)		Cycle
Dissipation =	(					+	Draw (watts)	)	x 3.415
(btu/hr)		Amplifier Efficiency (.65)

The value used for inefficiency is 1.00-efficiency. The factor 3.415 con- verts watts to btu/hr. Thermal dissipation in btu is divided by the con- stant 3.968 to get kcal. If you plan to measure output power under real- world conditions, the following equation may also be helpful:

Thermal			Total measured output power x .35		Quiescent Power
Dissipation	=		from all channels (watts)				x	3.415
				+	Draw (watts)
(btu/hr)		(				)
			Amplifier Efficiency (.65)

page 18 Operation Manual