# Setting amp's gain with multimeter?



## Vital (Feb 23, 2010)

Is there a way to set your gain correctly with a voltmeter let's say?? Or any other tool that would tell you exactly what's up?
Matching pre-amp output on your headunit with amp is sticky since there's almost never clear indications on amp's gain knob. Doing "raise your volume/lower your gain when u hear clipping" thing is just time consuming and will never get you that perfection u're looking for.....


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## gijoe (Mar 25, 2008)

Vital said:


> Is there a way to set your gain correctly with a voltmeter let's say?? Or any other tool that would tell you exactly what's up?
> Matching pre-amp output on your headunit with amp is sticky since there's almost never clear indications on amp's gain knob. Doing "raise your volume/lower your gain when u hear clipping" thing is just time consuming and will never get you that perfection u're looking for.....


Using a multi meter is much more time consuming and not helpful. You could use an o-scope, but that's even more time consuming and when you're all done it isn't really worth it.

Setting gains isn't difficult, I don't know why everyone wants to complicate it lately. Set them by ear and move on.


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## fonque (May 30, 2008)

Without measuring in some fashion, how can you know when your amps arent enough "amp"?
Since no one has ever demonstrated to me audibly what the difference is between clipping and not clipping, I dont know if I would actually be able to hear the difference before damaging something.


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## kyheng (Jan 31, 2007)

Getting speakers with high sensitivty of >88dB will be a good start. 
Getting amps with its output power > speaker's required power by 20-50% will be another step.
Then level match them slowly with your ears.


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## Cruzer (Jul 16, 2010)

i can hear clipping with subs, though im not sure i can hear clipping with speakers, but i hear distortion.

ive never blown a speaker or sub, and im a noob still, but imo u can tell if something is being clipped/distorted.


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## kyheng (Jan 31, 2007)

^Are you sure is your sub? Some time when you got some leak on the enclosure will cause this also.


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## sqshoestring (Jun 19, 2007)

If you play a low tone on most subs when it clips it will start to make a metallic sound. It will happen sooner than you think.

All you need to do is turn your amps way down, now turn the HU all the way up or until it distorts. Dial it around and find where it starts doing it (if it does). Set it maybe 5% lower and never turn it higher than that. Leave the HU there and turn each amp gain up until it starts to clip, you should minimize the time wide open it clips at of course. Now, listen to some music at your normal level and turn down the amp that is too loud to match them up. There you are done. The reason it is near impossible to set it with a DMM for music, is that music is at all different levels. When you consider radio/ipods/usb/cds/source recording levels/compression/etc it never comes out the same. So you need to be able to exceed the normal max to get the most out of a lower level source, and not turn it all the way up on a high level source that is maybe also compressed. 

So you often raise your gains a little higher than the above procedure gives you, so you can crank up the weaker source music...and it will distort/clip on stronger source music or tones. You don't want to play the HU higher because sending clipping to the amps is not a good idea.


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## ErinH (Feb 14, 2007)

the easiest method I've found is simple:
grab one of your speakers. set the headunit volume to 0. Attach speaker to amp. Turn gain up until you hear 'static'. 
Stop.

Play music. Is it loud enough? Does it sound distorted? 
Adjust gain as necessary.


I've found my gain settings are limited to signal-noise. By doing this, the SNR is very low (not audible once the speakers are installed), and the system is still loud enough for me.


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## Cruzer (Jul 16, 2010)

kyheng said:


> ^Are you sure is your sub? Some time when you got some leak on the enclosure will cause this also.


i have an aq1200d, which comes with a bass knob and on that knob it has a clipping light.

as soon as i hear clipping, i look at the knob and the light is blinking.



bikinpunk said:


> the easiest method I've found is simple:
> grab one of your speakers. set the headunit volume to 0. Attach speaker to amp. Turn gain up until you hear 'static'.
> Stop.
> 
> ...


does that work for subs too?


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## fonque (May 30, 2008)

bikinpunk in your experience does the clipping/distortion point of speakers happen before or after you hit the "hiss" point from turning up the amp gain?

Ive only tried this on my 100watt audiosource amp for my paradigm atom bookshelfs. And I had 2 different results. When I used the onboard sound card on my PC, I hit the hiss point waaaay before I heard anything I would consider distortion. However, that was not the case when I switched and starting using an audio-gd compass headphone amp/DAC as the DAC instead of the sound card.


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## ErinH (Feb 14, 2007)

IME, the clipping point is somewhere near (though, nowhere near exact) the clipping point. iirc, last time I tested my own amps, it was well under the clipping point, but there was still plenty of power available to have the volume I wanted without having to suffer from noise issues.


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## metanium (Feb 2, 2007)

Here's a tutorial I wrote up based on Mark Eldridge's demonstration at a get-together.

http://www.diymobileaudio.com/forum/diyma-tutorials/51435-setting-gains-w-o-oscilloscope.html


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## jf2oo6 (Feb 17, 2010)

How do you know when the hu is sending a clipped signal? How do you know what to make the max volume of the hu? I have heard the 75% rule, but how do you know if your hu can go higher than that before clipping?

For instance, my hu goes up to 40. Should I make the new max at 30, or maybe 35?


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## ErinH (Feb 14, 2007)

you won't know for sure until you load it and check with an oscilloscope.


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## kyheng (Jan 31, 2007)

If got machine to measure, it is better. But if without machine it will be hard to tell. Usually midbass or sub it will be more obvious when it is clipping.


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## storm (Jul 21, 2006)

Say you are running an active system with a processor. Amp gains are set with the Oscope. Switch on the system and you realised that the music is too loud at the preset volume. Lower the individual gains on the processor.

Now, does the above defeat the gain setting process in the first place?


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## diamondjoequimby (Jun 30, 2009)

I used to be in the set it by ear camp. After using a meter, then a scope over the past few years I'll never go back. It really isn't hard at all and by setting your limits you can then dial down by ear to balance everything.

It is especially beneficial if you are using multiple devices in the signal path w/ gain adjustments.

It makes the dynamic range of the system better and overall more reliable.

If you don't have a scope, the easiest way to do it with a meter is know how much power the amp is supposed to make (in watts) multiply that # by the impedance of the speaker to be connected, then take the square root of that # and that is the voltage you need to be at on the output side. Use a 0dB test tone in the range that the speaker is to play (i.e. sub use 40Hz)

so, if you have an amp rated at 50x4 rms @ 4ohm and are connecting to a 4 ohm speaker here is the math:

50x4=200 ->
sq root of 200 = 14.14 ->

so shoot for 14.14 vac out of the amp.

Only disadvantage of this vs. an o-scope is you are at the mercy of the manufacturer for the numbers. Most decent amps will do more clean power than they are rated at so you won't be maximizing the clean output, but at least you can be pretty sure the output will be clean.

If you want to build in some gain overlap, easy. Just use a -5,-10, or -15dB test tone when adjusting the amp.

On a side note, it is also important you know what the maximum unclipped output of the source unit. If you are clipping right out of the source, you are just cleanly amplifying clipped signal.


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## diamondjoequimby (Jun 30, 2009)

storm said:


> Say you are running an active system with a processor. Amp gains are set with the Oscope. Switch on the system and you realised that the music is too loud at the preset volume. Lower the individual gains on the processor.
> 
> Now, does the above defeat the gain setting process in the first place?


Setting the gain w/ a scope sets your top end limit. If it is too hot when you turn it on, back the gain off. Nothing ever blew up by turning it down.


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## MarkZ (Dec 5, 2005)

All you people worried about blowing something really need to choose different speakers. 

Anyway, please search the forum, guys! This question has been answered ad nauseum over the years. The quick answer is this: setting it by ear is the only correct way to do it.


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## diamondjoequimby (Jun 30, 2009)

MarkZ said:


> All you people worried about blowing something really need to choose different speakers.
> 
> Anyway, please search the forum, guys! This question has been answered ad nauseum over the years. The quick answer is this: setting it by ear is the only correct way to do it.


i thought this was the no dumb question section...doesn't it say right in the description ask away no matter how searchable?

But I digress...

Saying setting by ear is the ONLY way to set gains falls somewhere between ignorant and flat out wrong.


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## MarkZ (Dec 5, 2005)

I'm not the forum police. Not NARCing on people here. Just saying that if someone wants to know the answer, which is presumably the goal of the OP, then it makes sense to search the topic to see the long long discussions that have already been had a zillion times before. It beats having to sit and wait for responses to roll in. I know that when I'm looking for the answer to a question, I google search the **** out of it until I find the answer. If it's a car audio question, I search here. It's most likely been discussed at great length before, and then you can read a whole conversation about it. Pretty cool.

Anyway, I didn't say it was the only way to set gains. I said it's the only way to set gains _correctly_. 

[You actually CAN do it with a scope. But this involves first taking energy measurements of a selection of your music, and applying some known psychoacoustic thresholding to the result to achieve a target crest factor value... once you do that, you can then use the o-scope to set the gain. 99% of the people who use a scope to set gains assume a crest factor of 0dB, which falls somewhere between ignorant and flat out wrong. ]


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## evo9 (Jul 6, 2005)

My simply answer; Get a HU with 5 volts or greater line out signal. Then just just crack the amp gain "if you even need to" & leave it alone.





.


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## diamondjoequimby (Jun 30, 2009)

MarkZ said:


> I'm not the forum police. Not NARCing on people here. Just saying that if someone wants to know the answer, which is presumably the goal of the OP, then it makes sense to search the topic to see the long long discussions that have already been had a zillion times before. It beats having to sit and wait for responses to roll in. I know that when I'm looking for the answer to a question, I google search the **** out of it until I find the answer. If it's a car audio question, I search here. It's most likely been discussed at great length before, and then you can read a whole conversation about it. Pretty cool.
> 
> Anyway, I didn't say it was the only way to set gains. I said it's the only way to set gains _correctly_.
> 
> [You actually CAN do it with a scope. But this involves first taking energy measurements of a selection of your music, and applying some known psychoacoustic thresholding to the result to achieve a target crest factor value... once you do that, you can then use the o-scope to set the gain. 99% of the people who use a scope to set gains assume a crest factor of 0dB, which falls somewhere between ignorant and flat out wrong. ]


no, most don't know what a crest factor is...nor do they know that most things recorded in say the last 10 years have a crest factor in the single digits...lower if it has been compressed. By using 0dB tones, you can set it up to be as reliable as possible. If you know what you are listening to, and understand what distortion sounds like, setting up gain overlap has no drawbacks.


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## diamondjoequimby (Jun 30, 2009)

evo9 said:


> My simply answer; Get a HU with 5 volts or greater line out signal. Then just just crack the amp gain "if you even need to" & leave it alone.
> 
> 
> 
> ...


what if you have an amp that has an input stage that can handle up to 16 volts in?


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## MarkZ (Dec 5, 2005)

diamondjoequimby said:


> no, most don't know what a crest factor is...nor do they know that most things recorded in say the last 10 years have a crest factor in the single digits...lower if it has been compressed. By using 0dB tones, you can set it up to be as reliable as possible. If you know what you are listening to, and understand what distortion sounds like, setting up gain overlap has no drawbacks.


I agree. Most people wouldn't have the capability or interest to make those measurements with a computer. But that's what would be required in order to use an o-scope to set the gains CORRECTLY. "Correctly" being the key word. Setting it for 0dB peaks is a really bad strategy. Then you're using the gain adjustment as a limiter with no attack and decay, which isn't what it's meant to be. Buying an actual limiter and calibrating it, or an amplifier with a built-in limiter (like some of the McIntosh amps), can be useful. But it serves a completely different purpose.

This discussion has been had a thousand times in here...


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