How to Set Gain on an Amp with a Multimeter

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If you own a car stereo, you would like to get the most sound from your system which includes your amplifier. Setting your amp gain is a critical step in achieving maximum performance as well as protecting your system. Furthermore, the gain adjustment on an amp is among the most misunderstood concept in the world of car audio.

Usually, the primary purpose of a gain control is leveling match the head unit output voltage in order to gain structure of the amplifier to avoid clipping as a result of overdriven input. However, setting the gain on an amp is relatively easy. Due to that, we shall be discussing how to set gain on an amp with a multimeter in this article.

What is the gain?

Gain refers to the input level of a clip, whereas volume is the output. When recording audio, gain usually is the first control that a microphone signal will go through in a mixer as the levels are being adjusted. In amplifiers, the gain is expressed in decibels; it is 10x the logarithm of the output power divided by the input power.

Critical steps on how to set gain on an amp with a multimeter

Step1: Disconnect

It would help if you disconnected positive speaker wire from the positive terminal on your amplifier.

Step2: Turn off settings

Ensure that all the EQ settings are turned off or set to zero including; loudness, treble, bass, EQ functions, processing and bass boost.

Step3: Set to zero

Set your input sensitivity gain to zero. Most amps, this process is counterclockwise on to the farthest point. Furthermore, ensure that the input voltage selector is set to Low if your amplifier is equipped with one.

Step4: Set head unit volume

The head unit volume should be set to 3/4th of the maximum volume. Once this is done, set your radio volume to maximum and then multiply the number by 0.75. This process will provide you with 75% of the maximum volume.

Step5: Measure resistance

Measure resistance on the speaker you would like to connect the amp using a multimeter. Ensure that the multimeter is measuring Ohms. Take one probe of your multimeter and place it on the positive lead and the other one on the negative lead of your speaker. Check on the ohm resistance.

Step 6: Check output

Check for the recommended watts output on your amplifier manual using the resistance ohm you recorded on your speaker earlier.

Step 7: Calculate

Calculate the appropriate AC voltage output for your amplifier. This equation is solved as; voltage equals to the square root of watts multiplied by resistance. For instance, a 500W RMS amplifier at 2 Ohms will be calculated as; 500W RMS x 2 Ohms = 1000W. Take the square root of the 1000W, and the voltage should be 31.62V when running the amplifier with single gain control. Some amplifier features 2 gain controls which should always be treated separately.

Step 8: Disconnect from amp

Ensure that your speaker and the subwoofers are disconnected from the amp you are setting the gain on. Furthermore, ensure that the amp is connected to an electrical source.

Step 9: Set volume

Once step 8 is done, set your stereo to 85% to 90% of the maximum volume.

Step 10: Insert probes

Take your multimeter probe and insert it into an output terminal of your amp; ensure that the positive probe is in the positive terminal and the same goes for the negative probe which should be placed in a negative terminal.

Step 11: Test system

Test the stereo by playing a 60 Hz tone CD. You should then adjust the amplifier gain knob as you keep an eye on your multimeter. You should stop the reading once the multimeter reads the recommended AC output voltage. The desired AC output voltage should be the one you found while doing the math equation. By now, your amplifier gain will haven adjusted correctly.

Items you will require when setting the gain on an amplifier

Hearing protection

You will require muffs or earplugs when setting gain in a stereo since the system will be operating on output levels that are quite high. Without these essentials, you can develop hearing loss quickly as you increase the volume.

It is advisable to protect your ears since building a decent sounding system without having to hear it will be a waste of time and resources. Furthermore, since the output will be high as you set the gain, it advisable to carry out this activity in a location or at a time that it will not cause disturbance to others.


You will require having a CD with a proper test tone; it should be recorded at 0db reference level and must have several tests done. When testing subwoofer 50 to 60 Hz is the recommended level while 1000 to 1500 Hz will be ideal for the main stereo amp level. 

Input sensitivity switches

When your amplifier features a different input sensitivity, you should consider commencing by setting it to its highest setting. Usually, this is expressed in voltage. If you fail to set the amp to clip at these settings, try the lower one until you get the clipping point.


A multimeter is highly essential when it comes to measuring various electrical units from resistance to voltage. You will be able to find AC output using a multimeter in order to perform the equation when setting gain in your stereo.


When performing the math equation, it will be best if you have a calculator with you in order to get the right figures.

Amplifier, speaker and stereo

These are the primary items you will require in order to gain in your amp. Without these, there will be no gain to adjust.


This is one of the most accurate ways of setting gain using a multimeter in your stereo. You will be able to prevent distortion as well as clipping in your stereo. Apart from a multimeter, you might consider using an oscilloscope, which will show you the presence of clipping as well as distortion in your system.

However, using a multimeter in setting gain is relatively easy and much faster when compared to the oscilloscope. As we come to a conclusion we hope that this article will help you set gain with a multimeter in your stereo accordingly.

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