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MA Series Power Amplifiers
9 AC Power Draw andThermal Dissipation
This section provides detailed information about the amount of power and current drawn from the AC mains by
•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%.
•Quiescent power draw is 90 watts (an almost negligible amount for
•Quiescent thermal dissipation equals 105btu/hr at 90 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, short duration paging is 1%.
Here are the equations used to calculate the data presented in Figures 9.1, 9.2 and 9.3:
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| Total output power with all | x | Duty |
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AC Mains Power | = | channels driven (watts) |
| Cycle | + | Quiescent Power |
Draw (watts) |
| Amplifier Efficiency (.65) |
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| Draw (watts) | |
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The quiescent power draw of 90 watts is a maximum value and includes power drawn by the fan. The following equation converts power draw in watts to current draw in amperes:
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| AC Mains Power |
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| Current Draw | = |
| Draw (watts) |
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| (amperes) | AC Mains | x |
| Power |
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| Voltage |
| Factor (.83) |
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The power factor of 0.83 is needed to compensate for the difference in |
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phase between the AC mains voltage and current. The following equa- |
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tion is used to calculate thermal dissipation: |
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Thermal |
| Total output power with all | x Duty | x .35 | Quiescent Power |
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| channels driven (watts) | Cycle |
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Dissipation = | ( |
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| + | Draw (watts) | ) | x 3.415 | |
(btu/hr) | Amplifier Efficiency (.65) |
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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 measure output power under
Thermal |
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| Total measured output power x .35 | Quiescent Power |
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Dissipation = |
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| from all channels (watts) | x | 3.415 | |||
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| + | Draw (watts) |
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(btu/hr) | ( |
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Amplifier Efficiency (.65) |
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Operation Manual | page 29 |