Amplifier Efficiency And Supply-Side Power

Definition: efficiency is measured output real power divided by measured input real power over the same operating interval.

Core Relationships

Pin = average of vsupply(t) × isupply(t)
η = Pout / Pin
Ploss = Pin - Pout

For slowly changing DC supply conditions, matched terminal voltage and total current averages may be adequate. For dynamic conditions, capture them on a common timeline.

Measure At The Amplifier

Voltage belongs at the amplifier terminals. Current must include every positive or return path feeding that amplifier. Battery voltage and a clamp around only one of several conductors can produce a plausible but incomplete input-power result.

Match The Output Interval

The numerator and denominator must describe the same channels, load, waveform, frequency, duration, thermal state, and protection state. Do not divide apparent output volt-amperes by supply input watts and label the result efficiency.

Efficiency Is A Curve

Measure efficiency and loss versus:

output level
load and channel count
frequency or program spectrum
supply voltage
starting and operating temperature
fan, DSP, lighting, remote and auxiliary-output states

Class A, AB, D and other topologies describe operation; they do not create one universal efficiency percentage.

Thermal Interpretation

Electrical loss is stored and moved through semiconductor junctions, magnetics, capacitors, resistors, PCB copper, interface materials, heatsinks and airflow. A short test may end before the heatsink surface shows the full thermal consequence.

Report

Publish input power, output real power, efficiency, loss, terminal voltage, current, output level, load, channels, waveform, duration, temperatures, cooling state, supply sag, limiter or protection state, instrument bandwidth and averaging interval.