How to Tune an Amp with a Multimeter

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​A multimeter, also known as a multitester or a VOM, is a device that measures current, resistance, and voltage in a machine or an electrical appliance. Amp is the short form for the word amplifier, which is an electronic device whose function is to increase the power of a current or a voltage varying with time. In essence, it raises a signal’s amplitude.

Getting the best sound out of a car stereo or sound system can be pretty exciting and entertaining. However, tuning an amplifier has been long misunderstood because most people do not know how to gain adjustment control. Lack of gain control could lead to clipping as a result of output voltage not matching the input, which ends up not being overridden.

​We can all adjust an amp’s bass and gains by manually tuning it and listening to the sound it is producing. This method is, however, very tedious and not recommendable. Our ears are also unable to capture the minute distortions in the sound produced by a faulty amplifier. ​

9-step procedure on how to tune your amplifier to quality sound using a multimeter.

Step 1:

Get the items and devices needed to tune the amplifier ready. These items are listed below together with their purposes.

  • A multimeter – to tune the amplifier.
  • The speaker – connects to the amplifier during and after testing.
  • The amplifier’s manual from which you will refer the amp’s details.
  • Calculator – to sum up voltage measurement.
  • 60 Hz test tone CD or audio source.
Step 2:

Test the resistance of the speaker connected to the amplifier by using a multimeter. When beginning measurement, the meter should be reading 0. Insert the red lead into the VΩMa jack and the black lead into the COM. You can now turn on the multimeter.

The selector in the ohm (Ω) area moves to the position of reading 200. Before making any measurement, ensure the reading is 0, and the leads are not touching. This procedure portrays no resistance between the leads. Note down the readings when the naked circuit wires reach the leads.

If your reading is 1, the dial is supposed to be turned one position clockwise, severally. Keep turning the dial, if necessary, up to 2000k till you get another reading other than 1. Once you are done, record ohm resistance.

Step 3:

Carefully read through the amplifier’s manual to find out the recommended wattage output and compare it against the ohm resistance you found.

Step 4:

From the positive terminals on the amplifier, disconnect the positive speaker wires. Set all the EQ like bass, loudness, treble, and bass boost settings to zero or turn them off. Rotate the gain counter-clockwise till you get to zero.

Step 5:

Turn the head unit’s volume to more than half of the maximum volume. Find out the maximum volume of your stereo or radio from the manual and multiply that number with a percentage of more than 75%.

Step 6:

Calculating the required ac voltage for an amplifier is pretty straightforward. The formula is as follows; AC VOLTAGE = RESISTANCE (Ohm) × WATTAGE SQUARE ROOT. Assume a 600-watt amplifier at 2 ohms. In essence, that would be 600×2=1200. Calculate the square root of 1200; then, the voltage is supposed to be 34.641 in the case of a one gain control.

Amplifiers with two gain controls are supposed to be treated independently. If an amplifier is 200 W 4-channels, that will be 800 watts in total for two different amplifiers. The above equation is, therefore, only applicable when calculating the voltage and gain control per channel.

Step 7:

Disconnect the amplifier from the speaker, accommodating it. However, make sure the amp still connects to a power source. Before you proceed to do anything else, make sure that the two devices are already disconnected.

Between a range of frequency of 60Hz – 50Hz, put in a test CD that has its Sine -wave tone test at 0db. This test is well suited for a 1000Hz amplifier, a subwoofer, or any mid-range amplifier. Redo the test tone several times or set the head unit to replay the test tone continuously.

Step 8:

Ensure you adjust all the amplifiers in your music system with the close concentration on the VOM. This process will ensure the speakers give their best output and function properly. Reduce the volume on the head unit until it reads zero. After that, turn off the amplifier.

Step 9:

Take all the wires from the speakers and reconnect them to their positive terminals respectively. It is advisable to be careful during the process to avoid any damages, therefore, ensure all the cables connect correctly to the right terminals.

This precaution enables people to avoid unnecessary accidents. The speaker will not function when the wires are wrongly connected. Turn on the head unit and remove the test CD previously played. Play a song that you are familiar with and listen in for any distortion. These sound-bends come in the form of:

  • Hissing
  • Cracking
  • Whomping
  • Buzzing
  • whiffing

If the highs and lows of your music seem balanced, but your bass sounds seem like it’s coming from the far end of the stereo, it is appropriate to delocalize the amps filter. Delocalization is done by adjusting the amplifier’s low pass filter even lower.

Fine-tuning your filters enables you to smooth the roughness in the sound. For example, if the sound vocals are too deep, adjust high pass filters on the amplifier to incorporate more high notes. On the other hand, if the vocals sound too low, re-organize your high pass filters to include more low notes.

Wrapping Up…

The above process is also applicable to a 4-channel amplifier. This amplifier raises the level of sound, and consequentially produces a high quality of music. Despite the design and the type of amp you are using, a multimeter is the best device to tune it.

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