How to tune your amp!

[clutch1]

I found this and thought it was SUPER helpful and interesting! It's how to properly tune your amp with a Multimeter!

So you're going to need..
the MM
a 50hz test tone: http://www.bnoack.com/index.html?http&&&www.bnoack.com/downloads.html

Burn your tone to a CD, mp3 player, etc. Then head out to your car.
Unhook the woofers from the amp. Make sure your know what impedence you're running at the amp (2 ohm, 1 ohm, 2.66 ohm, etc), if you're not sure, disconnect the woofers, and use your MM on the ohms setting to measure the wires where they would plug into the amp (on the woofer side of course), and whatever you get, that's your impedance.

Next it's time to do math. You're going to be using the equation P=(V^2)/R.
P=watts, you pick the number, let's say you want 1000watts powering your subs.
R=resistance.. or impedence, this is the ohm load your subs are wired at.. lets say 1 ohm on a monoblock amp
V= voltage (AC), this is what you're going to be measuring in a second, but first you need to find what you're looking for

So plug it in and solve 1000= (V^2)/1ohm...
and get V = 31.6 V(ac)

Now, fire up your audio system (woofers still unplugged), turn it up the loudest you plan on having it on any given day (volume and bass EQ), and play the 50hz test tone.
Run back to your amp, set the multimeter on V(ac), and measure from the two outputs. Adjust your gain until you're at 31.6V.

Woo! Now you'll be giving woofers on a 1ohm load exactly 1000watts. This works for any setup, just math it all out and then tune.

Hope someone else found this interesting, just figured I'd share.

[bizarre179]

That is very interesting. I should give it a try. Thanks!

[Ryan from Ohio]

Actually tossing a DMM on a set of speakers leads wont tell you what Ohms your running at. You are measuring DC Resistance at that point NOT AC impedance- which is what the amp will be seeing.

How to Set Amp Gains with a DMM (digital Multi-meter)

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.

[clutch1]

ah, quite mistaken then, how do you measure then?

[Ryan from Ohio]

You cant measure AC Impedance. Its an average.

Take a DMM put it to Ohm and hook it to the speaker. Push the cone slowly and watch what happens...

[CarGodz]

Gee I seem to remember having written a "how to" on setting gains with a dmm... If I get some time later I'll put it up... There is also a "how to" for installing an amp that goes with it.

[clutch1]

Oh I didn't search, so my bad if you already did!

Ryan, it will indeed vary, because as you move the cone the coil moves in the magnet and produces a voltage.

[Ryan from Ohio]

Gee I seem to remember having written a "how to" on setting gains with a dmm... If I get some time later I'll put it up... There is also a "how to" for installing an amp that goes with it.

Look at the quote a little bit closer...

:lol: Dang old man. :lol:

[lonnie]

For those that don't understand the formula, this is the transposed version for voltage from the original posted formula by clutch.

V=SQRT(RMSwatts X speaker ohms)
So my example is V= SQRT(600wattsX2ohms)
V=SQRT(1200)
V=34.64
So I need to see 34.64 volts out of the amp to reach 600 watts rms.

[Fi-Alero]

This is a decent beginner way to set an amp, but defintly is not the best.

Sure, you are getting "x"rms at 50hz, but what about at other frequencies? Your impedance will change at every note.

So basically what I'm saying is that doing this method, you can guarantee that your amp is still going to clip at a range of frequencies. The best way to do it is by ear.

[CarGodz]

Look at the quote a little bit closer...

:lol: Dang old man. :lol:

lol at myself... The truth is for most a dmm (digital multi-meter) is the best way to set an amp. While some like to do it by ear, the problem with bass is that many times you cannot hear the distortion (especially at 3/4 or more volume) and since most don't have the money for an oscilloscope a cheap $15 (or less) dmm can save you a lot of trouble and money down the road.