# Setting Gain using a Multimeter Question



## tdog333 (Nov 14, 2013)

Just got a new sub, still using the old amp. Trying to set my gain using a multimeter. I am using this calculator

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My amp is around 500-550 RMS @ 2 ohms, this gives me around 31-33 volts before i clip according to the calc.

When i turn the gain all the way up and put the volume at the highest I would listen to it ever (around 23/35) I get 26 Volts from the channels. I cant even get to 31.

Should I just leave my gain all the way up then?


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## Jepalan (Jun 27, 2013)

What model and make of amp are you using exactly?


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## Old Skewl (May 30, 2011)

You need to turn the head unit up to around 30. Then adjust your gains,


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## tdog333 (Nov 14, 2013)

The amp is a rockford fosgate prime r500-1

the sub is a Pioneer Champion Series PRO TS-W3003D4


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## fcarpio (Apr 29, 2008)

Is getting a cheap oscilloscope from eBay an option?

Spomething like this:

http://www.ebay.com/itm/ARM-DSO201-...50321?pt=BI_Oscilloscopes&hash=item417cef9531










Maybe even cheaper if you find a used one.

If so, you would start with test tones at the HU and you would look for clipping, then dial back until clipping is gone. Them move your way down the path to set the proper gains though out the entire chain. If you get the oscope I could make a simple write up on how do I set gains my gains using it.


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## squeak9798 (Apr 20, 2005)

You don't need a DMM or an Oscope to set your gains. You are making this more difficult than it is. Set the gain by ear. Simple. Done.


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## fcarpio (Apr 29, 2008)

squeak9798 said:


> You don't need a DMM or an Oscope to set your gains. You are making this more difficult than it is. Set the gain by ear. Simple. Done.


And run the risk of blowing your speakers if you don't know what you are doing. Sure, go right ahead...


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## squeak9798 (Apr 20, 2005)

fcarpio said:


> And run the risk of blowing your speakers if you don't know what you are doing. Sure, go right ahead...


setting it with a DMM or Oscope isn't a guaranty of anything either, unless you use a 0db test tone. However, since that would leave the majority of the amps power on the table unused it also would severely limit the output of the system and that 500w amp turns into a 100w amp if you assume an average level of -6db for the source material. Nobody enjoys a system setup like that. 

So anyone with any common sense uses a -3db, -6db or even a -10db test tone to set the gain to get some actual power out of the amp(s). But that leaves open the possibility of clipping, doesn't ensure proper level matching with the rest of the systems, ignores the possibility that someone might add a couple DB of boost to the EQ somewhere which further reduces "unclipped" amplifier power, etc. 

All in all, unless you set up your system to NEVER UTILIZE IT, which no one with any sense does, then the possibility of clipping exists regardless. If you can't manage to identify unhealthy distortion from your speakers and setting it yourself then you are either going to have it setup "safe" but wrong, or your going to **** something up eventually anyways (Oh, this boost knob should be turned all the way to the right, right?). For the rest of the world that has common sense and can hear pretty well, setting it by ear is perfectly acceptable. *Hundreds of thousands of people throughout history have successfully set their gains by ear with no ill effects. *i haven't used a DMM for anything other than level matching for 15 years. It's certainly possible


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## fcarpio (Apr 29, 2008)

squeak9798 said:


> setting it with a DMM or Oscope isn't a guaranty of anything either, unless you use a 0db test tone. However, since that would leave the majority of the amps power on the table unused it also would severely limit the output of the system and that 500w amp turns into a 100w amp if you assume an average level of -6db for the source material. Nobody enjoys a system setup like that.
> 
> So anyone with any common sense uses a -3db, -6db or even a -10db test tone to set the gain to get some actual power out of the amp(s). But that leaves open the possibility of clipping, doesn't ensure proper level matching with the rest of the systems, ignores the possibility that someone might add a couple DB of boost to the EQ somewhere which further reduces "unclipped" amplifier power, etc.
> 
> All in all, unless you set up your system to NEVER UTILIZE IT, which no one with any sense does, then the possibility of clipping exists regardless. If you can't manage to identify unhealthy distortion from your speakers and setting it yourself then you are either going to have it setup "safe" but wrong, or your going to **** something up eventually anyways (Oh, this boost knob should be turned all the way to the right, right?). For the rest of the world that has common sense and can hear pretty well, setting it by ear is perfectly acceptable. *Hundreds of thousands of people throughout history have successfully set their gains by ear with no ill effects. *i haven't used a DMM for anything other than level matching for 15 years. It's certainly possible


I agree with you about the 0db test tone, I don't think I ever said I was using that kind of test tone. I also agree that you can setup your gains by ear if you know what you are doing, most of us don't know and run the risk of blowing speakers. What I don't agree with is that you cannot set the gains (and know you max levels) to the entire chain, I repeat, the entire chain (max hu volume, proc input gain, proc output gain and last but not least amp gains), by ear. If you can, I would REALLY like to learn how you do it by ear. 

That is why I prefer the oscope, to get the whole job done. Besides, for most of us blowing one speaker will be more expensive than buying the oscope, why cheap out?


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## fulletal7777 (Jun 11, 2014)

fcarpio said:


> Is getting a cheap oscilloscope from eBay an option?
> 
> Spomething like this:
> 
> ...


So this thing that you linked would get the job done pretty well?


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## ccapil (Jun 1, 2013)

To save me typing it out here's a Quote glasswolf pages;

"How to Set Amp Gains with a DMM

I’ve realized lately that although we recommend to many people that they should set the gain on their amp with a digital multi-meter (dmm), most may not know how. 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 (also called True RMS) (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"

as with the portable oscilloscopes etc, i wouldn't waste my money. You can get a good and accurate result with a DMM. The only thing it will not tell you, is when the signal starts to clip it will only give you the voltage you "should" have that u calculated using ohms law. I always use an attenuated test tone at least -10db, this will allow for gain overlap.


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## fcarpio (Apr 29, 2008)

While this is a very good write up I do have a few observations:



ccapil said:


> 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.)


We do now that all headunits are different and suggesting an initial volume range of 75% - 90% seems like a very wide selection. The oscope will tell you EXACTLY where to set up you initial volume based on the test tone you are using.



ccapil said:


> 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)


I had a three way active system, my subs were cut at 40Hz, just saying...



ccapil said:


> 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.


If you have a cheap DMM the results on the screen are going to swing, sometimes wildly.



ccapil said:


> as with the portable oscilloscopes etc, i wouldn't waste my money. You can get a good and accurate result with a DMM. The only thing it will not tell you, is when the signal starts to clip it will only give you the voltage you "should" have that u calculated using ohms law. I always use an attenuated test tone at least -10db, this will allow for gain overlap.


You are assuming everyone has a DMM. if they don't have one they are going to have to buy it. In which case I would say buy the oscope instead.

I think it is a good idea the we are going throught this discussion BUT I am affraid it is getting lost if not on their own threads. Maybe you should post this in its own thread, as I should with my method so people can rip it apart and turn it into a more sound (pun intended) method.


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## fcarpio (Apr 29, 2008)

fulletal7777 said:


> So this thing that you linked would get the job done pretty well?


Yes. As a matter of fact I just got new amps and I have to set my gains sometime this week. Maybe I will take this opportunity to do a wrtite up on how I do this.


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## ccapil (Jun 1, 2013)

^ thanks fcarpio. As I mentioned I don't take credit for the write up as it was pasted from glasswolf. It it still the best write up step by step I have seen using a dmm. 
I agree, the o scope is the BEST way of setting gains, IF you have one, but not everyone does, I assume most people do have a half decent DMM. I like to visually see the sine wave, but there will always be an arguement this vs that. As long the the end result is "little" clipping.


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## gijoe (Mar 25, 2008)

fcarpio said:


> While this is a very good write up I do have a few observations:
> 
> 
> 
> ...


I would agree with just about everything, except for "You are assuming everyone has a DMM. if they don't have one they are going to have to buy it. In which case I would say buy the oscope instead." A DMM is a FAR more useful tool than an o-scope. Having a DMM will help you with a lot of troubleshooting and make it very simple. I would recommend that if you don't have a DMM, buy one before getting an o-scope. It's just going to be much more useful.


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## fcarpio (Apr 29, 2008)

gijoe said:


> I would agree with just about everything, except for "You are assuming everyone has a DMM. if they don't have one they are going to have to buy it. In which case I would say buy the oscope instead." A DMM is a FAR more useful tool than an o-scope. Having a DMM will help you with a lot of troubleshooting and make it very simple. I would recommend that if you don't have a DMM, buy one before getting an o-scope. It's just going to be much more useful.


I am not going to argue with that. In MY CASE I use my cheap oscope more than my cheap dmm to the point that I am thinking about upgrading to a nicer oscope.


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