Crown Comprehensive Manual for Micro Tech Amplifiers: AC Power Draw and Thermal Dissipation

Micro-Tech Series Power Amplifiers

9 AC Power Draw and

Thermal Dissipation

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

•Amplifier efficiency at standard 1 kHz power is estimated to be 65%.

•Typical quiescent power draw for the Micro- Tech 600 is 65 watts; typical quiescent power draw for the Micro-Tech 1200 and 2400 is 80 watts.

•Quiescent thermal dissipation equals 222 btu/hr at 65 watts and 273 btu/hr at 80 watts.

•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 paging is 1%.

Here are the equations used to calculate the data presented in Figures 9.1, 9.2 and 9.3:

		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 figures provided in the opposite column are typical and include 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 power factor of 0.83 is needed to compen- sate for the difference in phase between the AC mains voltage and current. The following equa- tion 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 constant 0.35 is inefficiency (1.00–0.65)
			and 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 mea-
			sure 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)

Operation Manual page 21