How to Set Amp Gains with a DMM

[cargodz]

How to Set Amp Gains with a DMM

I’ve realized lately that although we recommend to many that they should set the gain on their amp with a digital multi-meter (dmm), most may not know how. And although there is a lot of information out there on “how to”, most of it is jumbled with mathematical equations that some may not be able to understand and then they just give up.

Here’s what you’ll need:
1) Digital Multi-meter that reads AC voltage (this does not have to be an expensive model, in fact most $15 models have this feature)
2) Calculator that has a square root button (looks like a little check mark with a tail, this also can be a cheap dollar store item as long as it has that button)

Use this equation to figure out voltage power output:
- Take the RMS wattage per channel and multiply by speaker(s) ohm load
- Now take that number and push the square root button on the calculator
Example: 50 Watts RMS x 4ohm load = 200, square root = 14.142135
So the voltage reading for our example on the digital multi-meter should be 14.1

Remove positive wire speaker wire from the amp (while some say this is not necessary, I recommend so as not to accidentally cross the positive and negative wires)

Next with your system turned “OFF”, turn the gain all the way down (counter clockwise)
Side note: Although Bass Boost is something that most do not recommend using, if intend to use this feature, turn Bass Boost “ON” after turning your gain down.

Now turn your head unit (stereo) “ON”, make sure that all equalization features (bass, treble, etc.) are set to Zero (0)

Set your head units volume to 85-90% - while some prefer to suggest 75%, I recommend 85-90% since most listen to music at no higher than 75% and this gives plenty of room to use equalization features later (remember that every adjustment on the head unit will adjust the voltage value and even though you thought you had it set correctly, the speaker(s) may receive a clipped signal once you increase any equalizing features (bass, treble, etc.)

Play a test tone 50-60hz (if you do not have a cd, tape, etc with a test track, then play your favorite song with similar features)

While playing the test track, use the dmm (set to AC voltage) on the positive output of the amp and slowly adjust your gain until it displays the voltage that you figured out earlier.

Now turn your head unit down and then shut “OFF”, re-install positive speaker wire to amp

You have successfully set the gain on your amp with a digital multi-meter and you may now turn your system up to a comfortable listening level (50-75%) and adjust equalization features to your liking. :)