Connect the 12v power supply to
the power wires on the amplifier. Connect the power resistors (dummy
loads) to all of the channels of the amplifier.
Set the gain controls for
all channels of the amplifier to the same level.
Either all of the way up or all of the way down
will probably be the easiest. You can make fine
gain adjustments at a later time.
Connect the tone (sine wave)
generator to all of the amplifier channels. Turn
the output level of the tone generator all of the
way down.
Turn the power supply on. If
it is adjustable, set it where you want it (12
volts, 13.8, 14.4 your choice).
Power the remote terminal of
the amplifier.
Measure the output voltage
of the D.C. power supply (it should be the same
as before the amplifier was turned on).
Set all equalization to the
off position and set all crossovers to full
range.
Set the output frequency of
the generator to any frequency that you want. I
generally use 100hz. You should always use the
same frequency or at least make note of the
frequency used during the test.
Slowly increase the output
of the tone generator until the output of the
amplifier is approximately 2 volts A.C. Now set
all of the gains to match the output of all of
the channels.
Connect the oscilloscope to
any channel (they should all be the same since
you tweaked them).
Monitor the output voltage
of the power supply, either with your volt meter
or by the digital meters on the power supply. If
the power supply doesn't have digital meters, use
a digital multimeter.
Slowly increase the output
of the tone generator while watching the
oscilloscope. Increase the level until the top
and/or bottom of the sine wave flattens out.
Reduce the level until the wave is 'clean' again.
Now see if the power supply
voltage has held to the preset value. Reduce the
output level of the generator. If the D.C.
voltage changed during the test, you must take
this into account. A well regulated supply will
have held the preset voltage.
Now connect the A.C.
voltmeter to the output terminals of one channel.
The channel connected to the scope would be a
good choice.
Again Increase the level of
the generator until just before the amplifier
starts to clip. Make note of the voltage reading.
Turn the power supply off.
Quickly disconnect the dummy
load of one channel and measure its exact
resistance while it is still hot. The value of
the resistor will change slightly as it heats up.
Now use the Ohm's law
formula, P=E^2/R. If we found that the amplifier
drove 35 volts A.C. across the resistor and the
resistor had a D.C. resistance of 4.08 ohms, the
amplifier produced 300.25 watts RMS.
P=35^2/4.08
P=1225/4.08
P=300.25 watts RMS
NOTE:
1.If the D.C. power supply does not hold its
preset voltage, the power output will be lower
than the amplifier is capable.
2.This test cannot be done using speakers in
place of the dummy loads. The speakers will give
you a false high reading at most frequencies.