Last Updated on September 18, 2020

Music is powerful, and a fantastic sound system makes it even better. Get the most out of your car stereo and sound system by setting your amp’s gains correctly. It not only protects your equipment but gives you excellent sound quality too.

You can set your amplifier’s gain by matching the head unit’s output A.C. voltage to the amp’s input voltage. This also prevents the clipping of sound.

To tune the gain controller, all you need is a digital multimeter, speakers, your amplifier’s manual, a calculator, and a CD or pen drive with a test tone. Here are the step by step instructions to tune an amp by different methods.

How to Tune an Amp with a Multimeter?

Step 1: Measure the speaker’s resistance using a multimeter

Test the resistance of the speaker you’ll be connecting to the amp using a digital multimeter. For this, cut off the power supply of the speaker. Then determine which terminal on the speaker is positive and which is negative. Connect the multimeter’s red probe to the positive terminal and black probe to the negative terminal.

Record the ohm resistance visible in the multimeter. Remember, the resistance of maximum loudspeakers is 2, 4, 8, or 16 Ohms. So, it is safe to note the closest one to the value recorded.

Step 2: Note the amp’s recommended wattage output

Pick up the amplifier’s user manual and find the recommended wattage output. Compare this against the ohm resistance of your speaker.

Step 3: Calculate the required A.C. voltage

Now, we need to find the target voltage for the amp. This is the output voltage at which we need to set the gain of the amp. To calculate it, we need to use a variation of Ohm’s Law, V = √(P.R.), where V is the target A.C. voltage, P is the Wattage, and R is the Resistance (Ohm).

Let’s assume that your manual says the amplifier should be at 500 Watts, and the resistance of your speaker, which you found by the multimeter, is 2 Ohms. To solve the equation, multiply 500 Watts with 2 Ohms to get 1000. Now use a calculator to find the square root of 1000, and your output voltage is supposed to be 31.62 V in case of a one gain control.

If you have an amplifier with two gain controls, then they are to be treated independently.

For example, if the amplifier is 200 Watts by 4-channels, use the power output of one channel for your voltage calculation. The voltage for each gain control is the square root of 200 Watts x 2 Ohms.

Step 4: Unplug all accessories

Unplug all the additional accessories, including speakers and sub-woofers, from the amplifier you are testing. Disconnect only the positive terminals to remember the set-up for when you need to plug them back.

Step 5: Equalizer settings to zero

Either turn off the equalizer of set all its settings like Loudness, Bass, Treble, Processing, Bass Boost, and Equalizer Functions to zero. This prevents the filtering of sound waves and hence, gives the maximum range of the bandwidth.

Step 6: Set gain to zero

For most amplifiers, the minimum setting is achieved by turning the dial in the counter-clockwise direction as far as it will go.

Steps 4, 5, and 6 leave the amplifier connected only to the power source.

Step 7: Set the volume to 75%

Turn the head unit to 75% of the maximum volume. This prevents the stereo from sending distorted sounds to the amplifier.

Step 8: Play the test tone

Make sure that the speaker is disconnected from the amp before moving further.

Now, you need a test tune to test your system. Play a test tone on the stereo that has its sine-wave at 0 dB. The sound must have a frequency of 50 Hz – 60 Hz for a subwoofer amp and a wavelength of 100 Hz for a mid-range amp. It can be created by using a program like Audacity or downloading it from the internet. (1)

Set the head unit such that the tone plays on a loop continuously.

Step 9: Hook up the multimeter to the amplifier

Set your digital multimeter to A.C. Volts and choose the range in which the target voltage is present. Connect the multimeter leads to the speaker output ports of the amplifier. The multimeter’s positive probe must be placed in the positive terminal and the negative probe of the multimeter in the negative terminal. This allows you to measure the A.C. voltage across the amp.

If the immediate output voltage displayed on the multimeter is higher than 6 V, then repeat steps 5 and 6.

Step 10: Adjust the gain knob

Slowly turn up the amplifier’s gain knob while keeping an eye on the voltage value displayed in the multimeter. Stop adjusting the knob as soon as the multimeter reads the target A.C. output voltage that you calculated earlier.

Congratulations, you’ve set the gain on your amp correctly!

Step 11: Repeat for other amplifiers

Make sure to adjust all the amps in your music system using this method. This will give you the output that you’ve been looking for – the best one.

Step 12: Turn the volume to zero

Reduce the volume on the head unit until it reaches zero and turns the stereo off.

Step 13: Plug everything back in

Reconnect all the accessories, like other amplifiers and the speakers, that you removed before setting the gain. Make sure that all the wires are connected correctly and then switch on the head unit.

Step 14: Enjoy the music

Remove the test tune from the stereo and play one of your favorite songs. Surround yourself with the gritty music and enjoy the perfect distortion.

How to Tune an Amp with a Multimeter

Other Methods to Tune an Amp

You can adjust your amp’s gains and bass boost by manually tuning it and listening to what sounds best. But this method isn’t recommended because we often can’t capture the minute distortions.

Conclusion

Using a digital multimeter for setting your gains is one of the most effective and easy methods. It enables you to set the benefit for almost all amplifiers. The best method to prevent any distortion in your system is to use an oscilloscope. It pinpoints all the clippings and distortions. (2)

With the best multimeter with you, we hope this guide helps you tuned in an Amp correctly.

You may also want to check and read the HOW TO section of this site for other guides using a multimeter that may help you in the future. A few of the articles include: How To Test a Capacitor with a Multimeter, and How to Test Battery with Multimeter.

References

(1) wavelength – https://economictimes.indiatimes.com/definition/wavelength
(2) oscilloscope – https://study.com/academy/lesson/what-is-an-oscilloscope-definition-types.html