How to tune an AMP with a multimeter

Whether on an early morning drive or late night cruise, playing music from your car’s stereo is one of the best feelings. What makes this even better is a good sound system that gives you everything the audio has to offer.

Tuning the gain on your amplifier the right way helps you achieve superior sound quality. However, a lot of people don’t know what an amplifier is or the right steps to accurately adjust the gain control.

This article presents you with all you need to know, including a step-by-step procedure on how to tune your amplifier with the use of just a digital multimeter. Let’s get right in.

Amp with a Multimeter

Why Is The Multimeter The Right Tool?

Also called a multitester or Volt-Ohm-Meter (VOM), a multimeter is a device used to gauge the amount of voltage, current, and resistance present in an electronic component. Using a multimeter is easy.

An amplifier, on the other hand, is an electronic device used to boost or increase the voltage, current, or power (amplitude) of a signal to a certain gain.  

What is gain on an amp? It is simply the measure of amplitude from the amplifier.

This is how the multimeter and amplifier come together. Tuning an amplifier just means changing the level of amplitude from your car’s speakers. This affects how well the sound comes out of the speaker and, in turn, your overall listening experience.

You could use just your ears to determine how well these sound signals come out. However, this isn’t the best way to get the best sound as minute distortions are sure to be missed.

This is where a multimeter comes in.

A digital multimeter shows you the exact level of amplification your sound signals are on.

Where you have specific values you aim for with your signal amplitude, a multimeter lets you attain these with relative ease.

Regardless of all these, it’s not as easy as it sounds. While tuning your amplifier, voltage from the head unit’s input must be the same as its output. This ensures that sound clipping is avoided.

Now that the basics are covered, let’s get right to business.


Tuning An Amplifier With A Multimeter

There are certain tools you need aside from a multimeter. These include

  • A speaker to test with the amplifier
  • The amplifier’s manual to know details about it
  • A calculator to accurately measure voltage sums, and 
  • A CD or other source that plays audio at 60 Hz 

All these have their respective uses while tuning the amplifier. However, you will also make use of a formula. That is;

E = √PR, where E is the A.C voltage, P is the power (watts) and R is the Resistance (Ohm). Follow these steps closely.

  1. Check The Manual For The Recommended Wattage Output

Your amplifier’s manual shows you information on its wattage output. This does not change and you want to note this down before proceeding.

  1. Test The Speaker’s Resistance

Resistance is measured in Ohm (Ω) and you want to take note of the Ohm readings gotten from the speaker. This procedure is simple.

All you have to do is insert the connectors into their respective jacks; the read lead connector goes in the VΩMa jack and the black connector goes in the COM jack.

Once this is done, you move the multimeter selector to the Ohms logo (usually represented with “Ω”) and ensure it reads 0 before making any other steps. This signals that the lead connectors are not touching. 

Now, you touch the exposed circuit components on the speaker with these lead connectors. This is when you take note of the Ohms reading on the multimeter.

Ohms resistance values hover around 2Ω, 4Ω, 8Ω, and 16Ω. Here is a guide to measuring your speaker’s resistance.

  1. Calculate Your Target A.C Voltage

This is where the formula mentioned above comes in. You want to determine your target voltage using the values of the amplifier’s recommended wattage and speaker’s resistance you noted down.

Here, you insert values into the formula. 

For instance, if your amplifier has a wattage output of 300 and you pick up a resistance of 12, your target A.C voltage (E) is then 60 (the square root of (300 (P) × 12 (R); 3600).

From this, you note that when tuning your amplifier, you want to ensure that the multimeter reads 60. 

Where you have amplifiers with multiple gain controls, readings for these are to be inserted into the formula independently.

 Now, for the next steps.

  1. Disconnect Accessory Wires

After determining your target voltage, you proceed to disconnect all accessories from the amplifier. These include your speakers and sub-woofers.

One tip while doing this is to disconnect only the positive terminals. This lets you know where to plug them back once all procedures are complete.

Before proceeding further, ensure your speakers are completely disconnected from the amplifier.

  1. Turn Equalizers To Zero

Now, you set all equalizer values to zero. By turning the gain knobs on them down (typically counter-clockwise), this gives you the maximum bandwidth range.

Equalizers include the Bass, Bass Boost Treble, and Loudness, among others.

  1. Set The Head Unit Volume

To keep stereo outputs clean, you set the head unit to 75% of the maximum volume.

  1. Play A Tone

This is the audio output from the CD or other input source you use to test and fine-tune the amplifier.

Whichever input source you use, you make sure that the sine-wave of your tone is at 0dB. The tone is also meant to be between the frequencies of 50 Hz to 60Hz for a subwoofer and at a wavelength of 100 Hz for a mid-range amplifier. 

Keep the tone playing in a loop.

  1. Tune The Amplifier

The multimeter is called into action again. You place your lead connectors on the amplifier’s speaker ports; the positive lead is placed on the positive port and the negative lead on the negative port.

Now you slowly turn the amplifier’s gain control until you get the target A.C voltage recorded down in step 3. Once this is achieved, your amplifier has been successfully and accurately tuned.

Of course, to make sure audio from your sound system comes out the cleanest, you repeat all these for all your other amplifiers.

  1. Reset The Head Unit Volume 

Here, you turn the volume on the head unit down to zero. This also kills the stereo.

  1. Reconnect All Accessories And Enjoy Music

All accessories disconnected in step 4 are then reconnected to their appropriate terminals. After checking that all connectors are correctly in place, you turn up the head Unit volume and blast the stereo to music you wish to listen to.

Final thoughts

From the above steps, you see that tuning your amplifier seems a little technical. Nonetheless, with a multimeter by your side, get the most accurate values that assure you of the best sounds.

Apart from the unreliable use of your ears, other methods to get rid of distortion include using an Oscilloscope

If all these steps prove a little difficult to follow, this video may help you out.