How to Test an Amp With a Multimeter

Hey there, fellow music lover!

Are you tired of your car or home audio system sounding subpar? It can be frustrating when your favorite songs don’t sound as good as they should. Do you suspect that your amplifier might be the culprit?
As someone who has been tinkering with car audio systems for years, I understand the pain points of not having a properly functioning amplifier.

Let’s face it:

Testing an amplifier can be daunting, especially if you’re not technically inclined. But don’t worry – I’m here to help.

In this post, we will dive into the technical aspects of testing an amp’s output voltage using a multimeter. Don’t worry if you’re not technically inclined – I’ll break it down in simple terms that anyone can understand.

So sit back, relax, and let me show you how to get the most out of your amplifier!

How to Test Amplifier Output With Multimeter

To start, you should verify that the inputs produce the correct signal or power.

Two wires from the car’s electrical system supply power to the amplifier.

One of these connects to the car’s 12V battery, and the other ground the vehicle. It stands to reason that the amplifier won’t function properly if it isn’t fed the correct amount of power.

  • Find the Input Power Source and Amplifier

You can find the amplifier in the trunk, under the dashboard, or behind a seat.

To top it all off, you learn which cables are responsible for providing juice to the amplification device. To find out how to do these things, you can look in the owner’s manual for your vehicle or amplifier.

  • Start the Car Engine

To acquire a reading from a wire, you must first heat it. The car’s engine won’t start until you start the ignition to the start position. 

  • Make a Detection using the Input Wires

Put the probes of your multimeter onto the wires you know to be the inputs, then switch them to the DC voltage setting.

Connect the multimeter’s positive red probe to the wire and the negative black probe to the ground. The voltage should sit somewhere around 11 and 14 volts for a reliable power source.

Perhaps you will need to run another test to find further information about your power source.

Turn up the radio while keeping the multimeter probes plugged into the car’s inputs.

Additionally, there might be an issue with the input source if the voltage reading doesn’t go up.

  • Fuse Check

A blown amplifier fuse is one possible cause of an inadequate power supply. Find the amplifier’s power fuse, switch your multimeter to the resistance setting, and touch the probes to both ends of the fuse to make sure it’s not blown.

To check whether you need to replace the amplifier fuse to be replaced because of a negative reading, just check the reading.

You may also have a look at our article on how to test a fuse without a multimeter.

Some amplifiers even include a fail-safe feature.

The power supply is faulty if it has this feature and enters safety mode when turned on.

As an example, if the amplifier is attached to or in contact with a conductive surface, this will activate a failsafe mode.

How to Use a Multimeter to Check an Amplifier’s Output

To test the amplifier’s output levels, position the multimeter’s probes on the terminals, and play a CD with 50Hz or 1kHz at 0dB in the source unit. The multimeter’s range should change to AC voltage between 10 and 100 VAC. The voltage reading that an amplifier provides should be perfect for the power output that is specified.

To elaborate, allow us to do so.

  • Disconnect the Speakers

To begin, remove the speaker cables from the amplifier’s output jacks.

Unplug the speaker cables to access these terminals for testing.

Disconnect or turn off any electrical crossovers that were wired into the amplifier’s output jacks.

As such, we can assure you that the testing will be free of disruptions.

  • The Volt AC Setting on the Multimeter

Car amplifiers are supplied by DC voltage.

If you want to check the outputs, you’ll need to switch your multimeter to the AC voltage setting, since this current is alternating. On a multimeter, the “VAC” reading indicates an alternating current.

To get accurate readings from your multimeter, you’ll also need to adjust this between 10 and 100 VAC.

  • Connect Multimeter Leads to the Amplifier’s Output Jacks

After you have done the first two steps, you can check the amplifier’s output by touching the probes of your multimeter to the terminals at the amplifier’s output.

The speaker wires were previously disconnected from these outputs.

To test the amplifier’s output, connect the positive probe to the amplifier’s positive terminal and the negative probe to the amplifier’s negative terminal.

However, if you want to utilize the amplifier in mono mode, just link the positive and negative terminals probes to the bridged output terminals.

  • Put it to the Test With a Frequency

Playing a test song is the simplest technique to apply a frequency for testing the signal outputs. To listen to music, you may either put in a CD or use any other input device you may have.

However, you must play this music at the correct frequency for the speakers you have.

When using subwoofers, a “0dB” tone at 50 Hz is ideal, whereas a “0dB” tone at 1 kHz is ideal for midrange or tweeter amplifiers.

An additional option is to employ a signal generator. To test an amplifier, you first remove all input and output connections, then connect the signal generator to the amplifier’s input terminals via RCA cables, and then position the multimeter’s probes on the amplifier’s output terminals.

After turning on the signal generator, you may tune the frequency to perfection for your headphones or stereo.

Once again, 50 Hz is ideal for subwoofer amplifiers while 1 kHz is ideal for midrange and tweeter amplifiers.

  • Check the Readings

After applying the test frequency and recording the result on the multimeter’s display, more analysis is necessary.

In most cases, an amplifier’s manual or the amplifier itself will specify a watt range, often between 50 and 200, within which the amplifier is supposed to operate.

To make comparisons, you must change your voltage to watts.

Watts may be determined by dividing E by R, where E signifies the voltage and R is the resistance. The resistance will be available on the amp’s chassis, or you can find it included in the user manual.

Consider a scenario in which your car has 8-Ohm-resistance subwoofers, resulting in a voltage measurement of 26. Subwoofers with an impedance of 8 ohms provide a load of 4 ohms on the amplifier.

If the watt is significantly lower than the amplifier’s watt output, the problem is in the amplifier and you should be serviced or replaced.

Frequently Asked Questions (FAQS)

  • How to use a multimeter to check out my car’s stereo system?

The DC Voltage setting on the multimeter is where you want to be when checking the vehicle radio amplifier. Activate the vehicle radio and adjust the volume to a comfortable listening level. Join the meter’s positive lead to the amplifier’s positive terminal and the meter’s negative lead to the ground. If there is a voltage drop close to 12 volts, the amplifier is functioning correctly. But, if this isn’t the case, there might be an issue with your amplifier.

  • Is there a way to test an amplifier to see if it has failed?

You can check for blown amplifiers in several different ways. Verifying that the fuse has not blown is one option. Most likely the amplifier is also dead if the fuse has blown. The amplifier making weird sounds is another telltale sign. If the amplifier is making popping or crackling sounds, it may be defective. Now you can see whether the amplifier has been physically damaged. Any evidence of fire or melting on the amplifier indicates that it has failed.

  • How can I test whether the amplifier in my vehicle is broken?

If your car’s amplifier is malfunctioning, you may usually tell in a few different ways. Checking for visible symptoms of deterioration, such as a cracked case or frayed wiring, is one approach. Another method is to listen for any popping, crackling, or hissing noises emanating from the amplifier.

You may not get the best sound from your vehicle’s audio signal if the amplifier is malfunctioning. If the sound coming from your stereo is distorted or muted, it may be because the amplifier is broken.

However, The best thing to do if you think your car’s amplifier is broken is to ask an expert to get it checked out by an expert mechanic.


Testing amplifier output of an amplifier using a multimeter is a simple process that may affect the sound quality. First, you take a reading of the AC voltage at the amplifier’s output terminals, and then you compare that reading to the amplifier’s power rating.

Check out our article on adjusting and testing amplifier gains with a multimeter to learn more about fixing faulty amplifier output by adjusting the amplifier’s gains.

Last Updated on March 15, 2023 by Danny Reid

Written by Danny Reid

Hey, I'm Danny, and I know how hard it can be to find the perfect audio gear. Need a new stereo, amp, speakers, or subs? Don't worry – my blog is here to help you cut through the noise! My mission is to give you the best reviews, so you can make the right decision for your audio needs. And if you ever get stuck thinking, "Where does this blue wire go?" don't worry – I've got tons of cool tips to help you out of any jam. So come along with me on this fun, sound-filled adventure, and let's find the perfect audio setup to make your tunes really sing!