How to check the output of an amplifier with a multimeter
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Car amplifiers help improve your listening experience, especially when it comes to music from your car or home stereo system.
Through the use of transistors, they amplify the sound signal from the input sources, so they are perfectly reproduced on large speakers.
Of course, when there is a problem with the amplifier, the car's audio system suffers.
One way to make a diagnosis is to check if the amplifier is producing the appropriate outputs, but not everyone knows how to do this.
In this guide, you will learn how to test the output of an amplifier with a multimeter.
Let's get started.
Checking Input Sources
The first step you want to take is to check that the appropriate signal or power is coming from the input sources.
The amplifier is powered by two wires coming from other parts of the car.
These include one wire coming from the 12V battery and another wire coming from the chassis ground of the vehicle.
If the right amount of power is not being supplied, you would expect the amplifier to be performing poorly.
- Find your amplifier and input power source
The amplifier is usually located under the dashboard, in the trunk of a car, or behind one of the car seats.
You will also find out which cable is feeding the amplifier. You can refer to the owner's manual for your car or amplifier.
- Turn on the car's ignition
You need the wire to be hot in order to get readings from it. Turn on the car's ignition to start without turning on the engine. It's enough.
- Take a reading from the input wires
Set the multimeter to DC voltage and place the test leads on the indicated input wires.
Place the red (positive) test lead on the positive wire and place the multimeter's black (negative) test lead on the ground wire.
A good power supply will give you readings between 11V and 14V.
Volume test
Further testing you can do may give you more information about your PSU.
While the multimeter leads are still connected to the input wires, turn up the volume in the car.
If you don't get any increase in voltage reading, then there is a problem with the input source and you are making further inquiries about it.
Fuse test
One problem with a bad amplifier power supply can be a damaged amplifier fuse.
To test this, you simply find your amplifier's power fuse, set your multimeter to resistance, and place test leads on both ends of the fuse.
If the amplifier shows a negative value, the fuse is bad and needs to be replaced.
You can also check out our guide to checking fuses without a multimeter.
In addition, some amplifiers also have a safe mode.
If yours is equipped with this function and goes into safe mode when you turn it on, then the power supply is faulty.
One case where safe mode can be activated is if the amplifier is mounted on or touching a conductive surface.
How to check the output of an amplifier with a multimeter
Insert a CD at 50 Hz or 1 kHz at 0 dB into the source box, set the multimeter to AC voltage between 10 and 100 VAC, and place the multimeter's leads on the output terminals of the amplifier. A good amplifier is expected to give voltage readings that match the recommended output power perfectly.
We will explain further.
- Disable speakers
The first step is to disconnect the speaker wires from the amplifier output terminals.
These are the terminals you want to test on, so disconnecting the speaker wires is critical.
In addition, you also want to turn off or disable any electronic crossovers connected to the amplifier's output terminals.
This is done so that there is no interference with the tests.
- Set the multimeter to AC voltage
Although the car amplifier is powered by DC voltage, the amplifier converts the low current/low voltage into a higher output signal reading.
It's alternating, so you set your multimeter to AC voltage to test the outputs. AC voltage is usually labeled "VAC" on a multimeter.
You can also set it in the 10-100VAC range to make sure the multimeter is giving correct results.
- Place the multimeter leads on the output terminals of the amplifier
After the previous two steps have been completed, you simply place the multimeter's leads on the output terminals of the amplifier.
These are the outputs from which you disconnected the speaker wires.
Place the positive test lead on the positive output terminal of the amplifier and the negative test lead on the negative output terminal.
If the amplifier is shunted or operating in mono, simply connect the positive and negative leads to the shunt output terminals.
- Apply test frequency
The easiest way to apply a frequency to test output signals is to play a test tune.
You insert a CD or simply play a tune from any input source you have.
However, the most important thing is that this tune should sound at the right frequency for the speakers you are using.
For subwoofers, you want to play a 50 Hz melody at "0 dB", and for mid or high frequency amplifiers, you need to play a 1 kHz melody at "0 dB".
Alternatively, you can also use a signal generator.
You disconnect all input and output wires from the amplifier, connect the signal generator to the input terminals with RCA cables, and place the multimeter leads on the output terminals of the amplifier.
With the signal generator turned on, you tune the frequency to the appropriate level for your speakers.
Again, you want 50Hz for subwoofers, or 1kHz for midrange and treble amplifiers.
- Rate results
This is where it gets difficult.
After you apply your test frequency and record your multimeter readings, you will need to do some calculations.
Amplifiers are expected to produce recommended output power in the range of 50 to 200 watts, and this is usually stated in the manual or on the amplifier case.
You convert your voltage to watts and make comparisons.
Formula for calculating watts
E²/R where E is voltage and R is resistance.
You can find the recommended resistance on the case or in your amplifier's manual.
For example, look at a situation where you are using 8 ohm subwoofers and you get a voltage reading of 26. In a subwoofer, 8 ohms is a parallel load of 4 ohm resistors on the amplifier.
Watt \u26d (26 × 4) / 169, \uXNUMXd XNUMX watts.
If the rated power does not match the recommended output power of the amplifier, then the amplifier is defective and must be checked or replaced.
Conclusion
Checking the output of the amplifier with a multimeter is easy. You measure the AC voltage produced at its output terminals and compare it to the recommended wattage of the amplifier.
One way to fix an amplifier's poor output is to tune its gains, and you can check out our article on tuning and testing amplifier gains with a multimeter.
F.A.Q.
How to check the amplifier for performance?
A quick check is to make sure the sound quality is good. Also, if the input power or sound sources are bad, you will have problems even if the amplifier is working perfectly. Test these sources.
What is the output voltage of an audio amplifier?
The expected output voltage of an audio amplifier is in the range of 14V to 28V for an 8 ohm amplifier. However, this depends on the input power and the type of amplifier used.
How to determine that the amplifier is burned out?
Symptoms of a burnt out amplifier include strange buzzing or distorted sounds from the speakers, and the speakers do not produce sound at all, even when the sound system is turned on.
How do you read amps with a clamp meter?
Place the wire between the probe sleeve of the current clamp, set the resistance range and check the reading. Make sure the wire is at least 2.5 cm away from the sensor sleeve and measure one at a time.
How to test DC amplifiers with a multimeter?
Insert the black lead into the "COM" port and the red lead into the "Amp" port, usually labeled "10A", depending on the multimeter. Then you set the dial to read DC amps.
