Tuning an Amp with a DMM?

[Ninesvnsicks 10+ year member]

Hey everyone so I want to tune my amp with my DMM I just don't know how to do it or where to start. I've looked at the other threads but they don't really seem to cover how to do it or where to start. I'd just like to know that I'm not over powering my subs and it's about time I at least set the gain properly.

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[bgowdy 5,000+ posts]

lol im with you on this one. ive read but dont understand really how to do. i do now know the amp output voltage i need to get my rms though.

 

[ItsAJeepThing 10+ year member]

Someone can chime in and correct me if im wrong but I believe this is how you would do it.

First, you will need a 50hz test note. You will want to find the voltage you need to set the gains at with the equation volts = sprt(wattsxohms). Unplug the subwoofers from the amp and put your dmm in the terminals. Keep the RCA's plugged in. turn the subsonic filter off. Then on your deck set all your eq settings to zero or flat. You will want your deck on the highest volume you listen to it at or some say 3/4 of the way up and make sure your bass knob to your amp is at max if you have one. Put the 50hz note on repeat and you should get a reading on the dmm. Turn the gain tell you reach the voltage you found in the equation. Example of equation would be sprt(1500x1ohm) so sqrt(1500) = 38.73 So you would turn the gain up or down tell you reached 38.73. Then reconnect your subs to the amp and you should be set. If doing it with a 4 chanell i believe evertything is the same but you will use a 1khz test note instead.

 

[bgowdy 5,000+ posts]

ok i was given a site that calcs it for me. mines 49 even. so i would turn the gain til it reaches 49 on the dmm. then how would i reset my subsonic filter?

 

[bgowdy 5,000+ posts]

because i was wondering if my amp puts out its rated rms. i was told they do or get very close to it and i was just trying to check.

 

[timma100 10+ year member]

Someone can chime in and correct me if im wrong but I believe this is how you would do it. First, you will need a 50hz test note. You will want to find the voltage you need to set the gains at with the equation volts = sprt(wattsxohms). Unplug the subwoofers from the amp and put your dmm in the terminals. Keep the RCA's plugged in. turn the subsonic filter off. Then on your deck set all your eq settings to zero or flat. You will want your deck on the highest volume you listen to it at or some say 3/4 of the way up and make sure your bass knob to your amp is at max if you have one. Put the 50hz note on repeat and you should get a reading on the dmm. Turn the gain tell you reach the voltage you found in the equation. Example of equation would be sprt(1500x1ohm) so sqrt(1500) = 38.73 So you would turn the gain up or down tell you reached 38.73. Then reconnect your subs to the amp and you should be set. If doing it with a 4 chanell i believe evertything is the same but you will use a 1khz test note instead.

Thank you very much for sharing //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif Cant wait to dial in my SAZ-1500, but wont the bass nob cause clipping?

ok i was given a site that calcs it for me. mines 49 even. so i would turn the gain til it reaches 49 on the dmm. then how would i reset my subsonic filter?

What was the website you used? I am doing the exact same thing

 

[bgowdy 5,000+ posts]

gimmie a sec ima go through my post and and find the link. i am at work so i may not be able to get the link but i will try

 

[bgowdy 5,000+ posts]

Gain Setting Tutorial - eCrack.net

this may or may not help because i could get the actual link im at work and the site is blocked(figures). but ecrack.net is were its at tho

 

[timma100 10+ year member]

Gain Setting Tutorial - eCrack.net
this may or may not help because i could get the actual link im at work and the site is blocked(figures). but ecrack.net is were its at tho

Alright thanks il start reading that, I just found another gain setting tutorial that says almost exactly what you said, except it says to turn the bass boost all the way down, and keep the subs connected.

Here is the link, http://forum.sounddomain.com/ubbthreads.php/ubb/showflat/Number/65167/page/1 if its blocked il post a quote for you.

We are going to use the equation solving for Voltage using Power and Resistance.
Voltage = SQRT(Power x Resistance)

Example:

I have a single subwoofer with 4 ohm DVC coils. I'll wire the coils in parallel for a 2 ohm load. The sub is rated for 500W RMS.

I have a single amplifier rated 500W x1 at 2 ohms. I want all of that power available (knowing that power will only happen for small durations).

Volts = SQRT (500W x 2 ohms)

Volts = SQRT (1000)

Volts = 31.6VAC

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Determine the maximum head unit voltage you want to use as follows:

1. if you have a factory head unit and factory speakers and are using a LOC for your sub amp, use the highest volume level you do for music (without distortion to the speakers).

2. if you have an aftermarket head unit powering factory or aftermarket speakers and are using the HU preouts for your sub amp, use the highest volume level you do for music (without distortion to the speakers).

3. if you have a factory or aftermarket head unit feeding a signal to amplifiers for speakers and subs, you need to verify the maximum unclipped, non-distorted output - or just use a 75% volume setting if you are unsure if your headunit is capable of 100% unclipped volume. You can verify this with an oscilloscope.

When setting a subwoofer amp - if your head unit is powering speakers, you really want to disconnect them or use a high pass crossover on them. however, this may not be realistic for you. if not, then your max volume setting may not be possible without distorting your speakers. don't distort your speakers for this exercise. use whatever volume you can that doesn't distort your speakers. This is not the ideal situation, to do it right you should put high-pass crossovers on speakers when you have a sub.

----------------------------------------------------------

Once you have the head unit max volume determined, and the test tone CD playing on repeat. Set the EQ to flat, turn off processing. Make sure the fader is centered, balance is centered, sub level controls are maximum (sub level is just attenuation anyway).

You can go back to your amplifier.

Disconnect any speakers/subs not associated with the channels being adjusted. Set the gain to minimum. Turn off any bass boost. With the DMM set to VAC (Volts AC), touch the DMM positive leads on the speaker outputs. Slowly increase the gain until the DMM reads the voltage determined above.

While you're increasing the gain - LISTEN TO YOUR SPEAKERS/SUBS!!! Listen for any distortion - popping, scratching, noises that go away when you turn the volume back down.

You can use resistors to load the amplifier so you get a more accurate reading (like in the eD video), but the resistor load bank must have a power rating greater than the output power expected. Most of you reading this won't have a load bank on hand, especially for loads over 500W. Don't worry. You should be able to leave the speakers/subs connected - you're listening for clipping and distortion anyway.

Once you have set the gain on all of the channels separately, all of the amps separately. Hook up everything as it should be - all speakers and subs.

Now listen to your system with music. Listen for balance between all of the speakers and subs. If you desire a more balanced sound (i.e. subs overpower speakers) you TURN DOWN GAIN on the loudest speaker/sub. DO NOT INCREASE GAIN past your set points determined above. Most head units have sub level controls, fader, etc. that allow you to attenuate the signal from your HU.

Now you can start introducing EQ, boosts, etc. Note that any bass boost more than 6dB can result in clipping or damage. You've already set the amp gain as high as it should be. Once you get your EQ and boosts set, you should check your gain setting once again. Excessive bass boost settings will cause clipping.

 

[bgowdy 5,000+ posts]

yea i never use the bass boost on my amp anyway, that can cause clipping. i just set my hu eq's on 0

 

[timma100 10+ year member]

yea i never use the bass boost on my amp anyway, that can cause clipping. i just set my hu eq's on 0

Cant wait to try this when I get home, I wonder whats going to cook first, my wiring, or my coils... lol By the way, this may sound stupid but. If I have two 400WRMS subs wired in parallel together, wouldn't I want to apply 800WRMS to the circuit?

 

[ahole-ic]

Gain Setting Tutorial - eCrack.net

 

[bgowdy 5,000+ posts]

Cant wait to try this when I get home, I wonder whats going to cook first, my wiring, or my coils... lol By the way, this may sound stupid but. If I have two 400WRMS subs wired in parallel together, wouldn't I want to apply 800WRMS to the circuit?

thats sounds right. just use the site to get the output for 800rms. and eCrack.net - Car Audio SPL - News, Guides, Forums, & Competitions guy gave me this to begin with amd thats the link

 

[timma100 10+ year member]

I'm reading some conflicting information between ECrack and SoundDomain, SD says to multiply wattage by resistance then find the square root. EC says to devide. Wattage is determined by amperage X voltage so im not shure who to go with. The calculator on EC contradicts what he said in the post lol, it multiplies wattage by resistance then finds the sqrt, I assume it was a typo.

First you calculate at what voltage your amplifier is putting out full power at the impedence of the subwoofers. The formula for this is to divide the RMS wattage of the amplifier by the impedence of the subs and then take the square root of that. This will give you the voltage you need to shoot for. Being off by even the tiniest of increments can make a big difference in output, so try to be as close as possible.

He must have meant multiply right?

 

[ahole-ic]

I'm reading some conflicting information between ECrack and SoundDomain, SD says to multiply wattage by resistance then find the square root. EC says to devide. Wattage is determined by amperage X voltage so im not shure who to go with. Any advice?

I wrote a calculator to do it for you there... so you as long as you plug your numbers in there you'll be fine.