Crown Audio STUDIO AMPLIFIER owner manual AC Power Draw and Thermal Dissipation, Studio Reference

Studio Reference I & II Professional Studio 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 Studio Reference amplifiers and the amount of heat produced under various conditions. The calculations presented here are intended to provide a very realistic and reliable depiction of the amplifiers. The following assumptions were made:

•The amplifier’s available channels are loaded, and full, standard 1 kHz power is being delivered.

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

•Quiescent power draw is 90 watts (an almost negligible amount for full-power calculations).

•Quiescent thermal dissipation equals 307 btu/hr at 90 watts.

•Duty cycle takes into account the typical crest factor for a particular 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 uncompressed 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 pre- sented in Figures 7.1 and 7.2:

The estimated quiescent power draw of 90 watts is a maximum figure, and assumes the fan is running at high speed. 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 constant of 0.83 is needed to compensate for the difference in phase between in the AC mains voltage and current. The following equation was used to calculate thermal dissipation:

Thermal		Total output power with all	x	Duty	x .35		Quiescent Power
		channels driven (watts)		Cycle
Dissipation =	(					+	Draw (90 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 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 be helpful:

Thermal		Total output power with all	x	Duty		Quiescent Power
		channels driven (watts)		Cycle x .35
Dissipation =	(				+	Draw (90 watts)	)	x 3.415
(btu/hr)
		Amplifier Efficiency (.65)

Studio Reference I

L O A D

	8 Ohm Stereo / 16 Ohm Bridge-Mono / 4 Ohm Parallel-Mono					4 Ohm Stereo / 8 Ohm Bridge-Mono / 2 Ohm Parallel-Mono
	AC Mains	Current Draw (Amps)		Thermal Dissipation		AC Mains	Current Draw (Amps)		Thermal Dissipation
Duty	Power					Power
Cycle	Draw	100-120 V	220-240 V	btu/hr	kcal/hr	Draw	100-120 V	220-240 V	btu/hr	kcal/hr
	(Watts)					(Watts)
50%	1325	15.9	7.2	1,780	450	1,925	23.1	10.5	2,500	630
40%	1075	12.9	5.9	1,485	375	1,555	18.7	8.5	2,060	520
30%	830	10.0	4.5	1,190	300	1,190	14.3	6.5	1,620	410
20%	585	7.0	3.2	900	230	825	9.9	4.5	1,185	300
10%	340	4.1	1.8	605	155	460	5.5	2.5	745	190

Fig. 7.1 Studio Reference I Power Draw, Current Draw and

Thermal Dissipation at Various Duty Cycles

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