Setting gains with dmm

[SWFL 10+ year member]

use a o-scope best way to see exactly when an amp is clipping, and yea i forgot the ..........

 

[Buck 5,000+ posts]

There has to be some mathematical equation. I mean, the amp is seeing 14.4v. The rca is, for example, 2v. The frequency of the tone being played is say 50 hz. With all these known #'s there's got to be a formula to figure it out.

 

[SWFL 10+ year member]

yea but music doenst play a constant 50hz tone so its impossible

 

[Buck 5,000+ posts]

Yeah I realize that put I can play different test tones. Say if I want to burp at 30, 40, 50 hz I could set my amp to get the most power out of it as possible without messing anything up. Obviously there would be no way to completely figure the rms out for every note, but I can at least get close. If I know certain things, like my rca input voltage and my power voltage from my battery and the resistance of the sub, I don't see how I couldn't make a guesstimate. Yes I realize all of these things change, but they don't change enough where I couldn't at least make at least a general guess at where my wattage is.

****. Someone needs to just come out with a simple + and - things you plug in and it tells you everything, lol.

I wish

 

[Buck 5,000+ posts]

I'm going to do some testing tomorrow. Is there a tool to measure the current being drawn by the amp? (you know like 100 amps)

 

[JimJ 5,000+ posts]

With all these known #'s there's got to be a formula to figure it out

Ohm's Law.

Is there a tool to measure the current being drawn by the amp? (you know like 100 amps)

A clamp meter.

However, simply knowing power output at a specific frequency doesn't tell you anything about whether the amp is clipping or not, which is where having an ear for distortion or an o'scope comes in //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Buck 5,000+ posts]

Oh ya I realize this. I wasn't even trying to figure out distortion or clipping. Just trying to see what kind of wattage I was giving my sub. Regardless, with me and my OCD, I'm going to try to find some sort of way to measure this somehow. But worst case scenario I learn a few things in the process.

 

[dman4486 5,000+ posts]

I would bet that if you put an O-scope on the amp with that test tone, you would be clipping.

this was setup as a daily on music correct? then yes you will be clipping and the dmm will show a much higher voltage as the input is much higher with tones.

 

[Buck 5,000+ posts]

I would bet that if you put an O-scope on the amp with that test tone, you would be clipping.

this was setup as a daily on music correct? then yes you will be clipping and the dmm will show a much higher voltage as the input is much higher with tones.

Yes but this was with a higher volume on the head unit than I listen to. I don't listen to my system quite as loud as I had my h/u up to. I don't think I am clipping, at least not a lot. The gain is at half and there is no bass boost, the sub level on the h/u is 0 and so is the bass. The only variables that I see are the gain and the music itself in this situation.

 

[kmanian 5,000+ posts]

Buck,

the gain being at half has little to do with clipping. The gain is to match your the voltage of the output of the rca from the source and the input of the amp. If you have stupid voltage going to the amp, half gain would probably put it into clipping.

but I do understand your looking for a wattage # not necessarily clipping.

 

[Buck 5,000+ posts]

ya and i'm going to test the v of the rcas. but unless the v of the rcas is crazy high, i doubt there is a lot of clipping i any at all.

 

[kmanian 5,000+ posts]

usually the v at the rca is much less than the specs say. I have seen HU's that say 5 volts actually only putting out 1v. but at the end of the day, as I told you when you were here, I have to agree with the person that stated do it by ear, 90-95% of the time I set the gains by ear.

 

[Buck 5,000+ posts]

Ya I gotcha. Just messing around, lol.

 

[Buck 5,000+ posts]

When we gona do some box testing?

 

[smoka 10+ year member]

There has to be some mathematical equation. I mean, the amp is seeing 14.4v. The rca is, for example, 2v. The frequency of the tone being played is say 50 hz. With all these known #'s there's got to be a formula to figure it out.

Like JimJ mentioned Ohms law.

Its a very simple equation. Power (watts) = Current x Voltage.

Just measure the voltage with a dmm and the current with a clamp meter. Multiply those together and you will get the answer of how many watts you are putting out. (+/- the tolerances of the meters you are using)

All of those input variables such as varying battery voltage, rca voltage, amp efficiency, load impedance, etc. will be too complex for the average enthusiast to use to calculate the output from (at least without adequate test equipment and strong electronics background.) But all of those input variables can be used to get more power out of your amp but you have to be careful about clipping and distortion.

If you get more watts than your amp is rated, then you're likely getting distortion which I believe can be measured with an oscilloscope (never tried it). Its also called THD (total harmonic distortion), most amps can output much more than they are rated but the THD % would be unacceptable to consumers. I think most amps are rated for output at 1% THD iirc.

Also you said you have a 1 ohm load. Usually subs are not that accurate in their impedance and you most likely are in the 0.8 to 1.2 ohm range, but you can check that with your meter also.