How
to measure and calculate output power of power amplifier
There are three output powers commonly
used, rated output power, maximum output power and music power. Here is tube
amplifier as an example.
1. Rated output power (RMS): When
power amplifier frequency characteristic and harmonic distortion coefficient
can reach the specified technical specifications (generally tube power
amplifier distortion should be less than 1%), power amplifier can work continuously
for a long time safe continuous sinusoidal signal power.
2. Maximum output power (PM): it can
meet the basic parameters that Maximum output power of the power amplifier at
the rated load resistance.
3. Music Power (MPO): the
instantaneous power value that power amplifier can output when Input a large
dynamic music signal and keeping that there is not voltage drop of amplifier
power supply. This MPO power is typically 4 or 6 times RMS power.
The output power of tube power amplifier is
measured by output a 1 kHz sine wave signal from audio
signal generator to input to power amplifier to be measured through the
attenuator, and send to input end of the measured channel is placed at the
maximum position, and other channels are placed at the minimum position, and its
tone control is placed at normal position as shown. Then connect a distortion
measuring instrument to output terminal of rated load, increase input signal
voltage, make the harmonic distortion coefficient of output voltage reach the corresponding
specified value, and finally measure the output power under normal operation and
continuous signal.
 |
| How to measure and calculate output power of power amplifier |
Output power measurement method
block diagram
The output power is calculated as:
P=U2/RL.
If the power amplifier is placed
under an 8 ohm load and its output signal voltage is 20v and the distortion
factor is 1%, so its rated output power (RMS) of the amplifier is
P= U2/ RL =202/8=50W
In addition, in order to simplify
the method of output power of tube power amplifier measurement, we can use the
method shown in the figure below to make measurements. The specific method is, placing
the measured work in a normal working state, the volume potentiometer is placed
at the maximum position, and the music signal output form CD player or the
record player or the signal of 1 kHz signal generator self-made is input to the
input end of the measured power amplifier, is connected to an 8 ohm speaker or
an 8 ohm load resistor at output end of tube power amplifier, and the dynamic
voltage across the load is measured by an AC voltmeter or a multimeter AC 20V gear.
The average of measured value is its output voltage.
If a tube power amplifier is placed
at both ends of the speaker load and the output AC voltage is measured as 10v,
the estimated power of its power amplifier is
P= U2/ RL = 102/8=12w
