Amplifier setup

[mesadude]

turn the volume on the amps all the way up, and the volume on your mixer down

[Manfrensengensen]

The proper way to gain stage a mixer and amp:

Unplug the speakers from the amp and turn the amp ch volumes down.

I use a pink noise tone generator on my Iphone, or the stlye of music
you will be playing thru the system.
patch it into input 1/2 line in. Solo/PFL the channels
set the preamp trims so the meter is at 0.
Turn the faders on ch 1-2 up to 0/unity.

Bring the mixer master fader up to just below peak on the master meters,
this could be +10 to +15 depending on the quality of your mixer. Usually
I set it so the last LED before the peak flickers momentarily.

Now slowly turn up the amp volumes until the clip light barely flickers,
then turn them back 2-3 clicks to give yourself a couple db saftey margin.
Make note of the volume position and turn them back down.

Turn down your mixer master and plug your speakers in. Turn your amp volumes up to the noted position.

Running an amp for a long period with no speaker load is not a good idea,
but most modern amps it won't hurt it to do this monentarily to set levels and turn it back down.

Now your gain stage is set correctly so your mixer output/master fader
will clip at near the same point as your amp. So if you need to run it up to just below peak you know your amp has the same amount of headroom.

[BajenKeno]

Great post! Thank you.

[mesadude]

And how many systems have you tuned?
That's exactly how it should NOT be done :-)

Leaves you zero headroom on the preamps mixing desk ,zero headroon on the master and zero headroom on the amp-input..

Also: built in protection circuits in the amps will most likely not work when amp isn't on..

ALWAYS put the amp volume on maximum!

So what if your masterbuss doesn't go to +15! At least you'll have headroom to spare..

[Manfrensengensen]

ummm...........nope.

First off there is no step mention that say to turn the amp OFF.

My headroom is at least 12db when you run the mixer properly at 0 to +3 db range.
Your mixer may vary and you would have less headroom if is clips at a lower level.

Feel free to Email DBX and tell them, their Gain staging guide is wrong.

I have yet to setup a system where the amp volumes are wide open.

[mesadude]

Which will be insufficient when you start working with a live dynamic source instead of pinknoise or a cd-track..
Not to mention combining 24+ tracks into the maser instead of only one.
Eventually you'll lack power and will be wanting to turn up the amps during show..

And even if the headroom wouldn't be an issue ,there's still the problem of protective circutry not being active in the amps..

Oe what about the guy who's mixing the next band? Maybe he'll go 5db louder? Running to the backstage already to turn up amps?

Just go to ANY venue in the world and ask to see their amp-settings..
Any festival, any club or stage..

But hey, just keep working as you see fit..
Just tell me which brand of speakers you use ,so i can buy shares.. gonna make a fortune on blown tweeters..

The only way your sytem works, is if you are the only one who is mixing on you own system..

[johnnyv]

I don't know why you would have run that test without the speakers?? There's an inter-reaction between the power amp and the speakers. I've never done a test like that ( I too just crank it to 11) but I can only imagine the peak light would not even come on without a speaker load?? right??

To the OP.
Turn it up but try and put the power amp on stage where you can see the peak lights from the FOH mix position. If the peak lights are coming on you will have to turn something down. Try cutting some low end from the mix if the amps are powering full range speakers. Power amp peak lights are another factor for keeping a handle on good sound.

[Manfrensengensen]

You do it without the speakers so you don't damage your hearing or the speakers.

The clip light indicates the input level, not the output level.

20+ years doing live sound off and on. I've never toasted an amp or speaker.

[TRoAudio]

The way that I recommend doing this is to turn up the amp channels all the way, set all of your mixer faders to unity, and turn all of the mixer preamps all the way down. Then, when you do a soundcheck, start by turning the preamps up one by one until each channel has been set to a sort of rough mix. This will set the board up to maximize the throw of the faders for you so you're not running any of the faders really high or low and will make it easier to mix.

If you find that a lot of your preamps are still down at a really low level, then you can go back and turn the amp channels down a bit. When the preamps are set very low, they can introduce noise and will be very sensitive to any adjustment you might make.

[Manfrensengensen]

Read for yourselves. The first pre amp stage you should strive to get the greatest signal to noise ratio, of course with some headroom.

I guess Rane, and DBX know nothing about audio.

Everything I have been trying to convey is here:

http://www.rane.com/note135.html

[mesadude]

In studio, yes..
Live i don't give f*** about S/N ratio..

No use in gaining extra 20dB to get the faders down afterwards..

All faders on unity, amps on max, and then just gain to taste..
Most of the time you'll find your vocal and bassdrum near inputclip..
Which means there is no room for turning amps down..

I don't know the venues you work, but in my case 98% of the venues don't have power left..
And i'm not a loud mixer..

I always find it strange when live engineers gain hihat to clip, and afterwards put fader on -40db..
Just isn't practical..

And yes, whatever you say is theoretically the best way to handle a system.
Welcome to LiveSound! Paper doesn't count here !

[TimmyP1955]

The common wisdom is to set up the gain structure such that everything clips simultaneously. Unless the system has a LOT of headroom over what you'll need, I disagree with this methodology. Most "weekend warrior" systems will occasionally (if not often) be run hot enough that there will be a little amp clipping. This can slip by relatively unnoticed if it's not too much too often. However if something else in the system clips at the same time, it will sound BAD. You want headroom in everything ahead of the amps so that there is no chance of clipping anyplace else. If you are using system limiters, this this is especially important.

Most boards and processors can put out around +22 dBu. I recommend that the gain structure be set up such that the amps clip with the board and processors no hotter than say +12 (consult your owners manual to figure out where on the meters that is - some have 0 = 0 dBu, some don't). This will give you a 10dB margin between board/processor clipping and amp clipping. Then of course don't forget to set those DriveRack limiters. You'll be able to push the system with minimal sonic degredation.

(My amps are rated at three times the continuous ratings of the speakers, and the amps clip with an input of about +12. The DriveRack limiters are set to brickwall with the amps' output at a bit less than the speakers' ratings (Peakstop is NOT used, as it distorts the signal). The subs amps' clip lights sometimes blip with the kick. Yet the subs are not being pushed into overexcursion and everything sounds fine. If I was using the "everything clips at once" method, I expect that it would sound pretty ratty. Same with the monitors - a vocal blast can blip the clip lights on the monitor amp (800W amp into a 150W monitor) in spite of the limiter that is set at about 125W. If something else were clipping too, it would be nasty for a moment.)


If you run the amps full, if they get messed will, things will get quieter - no biggie.

If you run the amps at less than full, the amps can be turned up. Your DriveRack limiter setting for that bandpass has just gone out the window. If this happens to be the sub, you might just think that the room is really something on the bottom end.

If your DriveRack is set at unity, there's still a loss, as the energy that went in is split into bandpasses (and there's the EQ cuts too). Look at the meters and you'll see that the outs show lower than the ins. To get the output meters on the theater's DSP to read the same as the input meters during a typical rock show, I had to run the DSP's outputs up somewhere between 7 and 10dB. To do otherwise would mean that the DSP input would be the first thing in the system to clip - not the outputs of the amps as it should be. The same thing happens if you are using the DSP in your poweramps instead of a separate DSP - it's very easy to end up with the inputs clipping before the outputs - a decrease in headroom if you have everything ay unity.

[noodle650]

always amps full up, then control separate Low/mid/hi channels from crossover, there are built in limiters and protection circuits in amps for a reason. if your clipping your mixer that hard something aint right!

[jasonraboin]

99% of the time the amplifiers are all the way up.

One exception is when the processing is in the amps. Then you have the highs at -9, subs at +4, or whatever the manufacturer tells you to set them at for a particular speaker.

I suppose setting all the gains to +32db might count as turning the amps down as well.

The other exception is when I'm doing monitors and there is a lot of noise and a lot of headroom. In those cases I will turn the amps down. I mostly mix quiet stuff.

Oh, and the other case might be if for deployment reasons I am given an amp that is capable of blowing up the speakers. If it's a fill or something like that.

It never has anything to do with clip lights.
Rane and DBX should give a call to L'acoustics or D&B.

[Red_Shift]

Originally Posted by jasonraboin

Oh, and the other case might be if for deployment reasons I am given an amp that is capable of blowing up the speakers. If it's a fill or something like that.

But you know this won't have any effect on power output right? if someone drops a mic while its hot, it'll still have the same effect. Why not throw a limiter before the amp in the signal chain?

[jklaff]

Stating how many years I've been doing this seems to irk some people so let's just say a really long time...

In a live reinforcement scenario I have always, always turned the amps all the way up. I cannot remember a single situation that required me to back off an amp at the amplifier itself and yes, most amps have built in protection. I have never blown out any speakers.

That said, if it makes any difference, I generally run a bank of compressors post crossover, pre-amplifiers for many reasons, one of which is a little extra protection.

[jasonraboin]

Originally Posted by Red_Shift

But you know this won't have any effect on power output right? if someone drops a mic while its hot, it'll still have the same effect. Why not throw a limiter before the amp in the signal chain?

I did not know that if I have something like a QSC PL4.0 on a little 8" fill box, and someone drops a mic, that if I have the gain down at like 12 o'clock, it would have the same effect if it were all the way up. That seems unlikely.

[Red_Shift]

Originally Posted by jasonraboin

I did not know that if I have something like a QSC PL4.0 on a little 8" fill box, and someone drops a mic, that if I have the gain down at like 12 o'clock, it would have the same effect if it were all the way up. That seems unlikely.

It's not at all. Dropping a mic will be one of the highest signals you can get, which will then splat all over your console, and then send that signal to the amp. It'll probably be +18 or +21 (depending on your console's headroom) which will then still clip your amp.

If you want to protect your gear use a limiter, don't attenuate your amp signal.

[ears2thesky]

+1 All the way up.

[Steve_B]

To the original poster.

If you turn up your amplifiers all the way, as advocated by some here, it will work. You are unlikely to blow anything up if you are sensible.

If, like others advocate, you only turn the levels on your amplifier part the way up, it will still work and again, if you are sensible, nothing is likely to blow up.

Not having the levels flat out means that you need a larger signal coming into the amp to achieve full power out. Maybe you can achieve the levels you require without needing to use every last Watt from the amplifier. As long as nothing is clipping further back down the line and the PA gets loud enough this is fine and you will achieve a slightly better signal to noise ratio. The main disadvantage is if the level on the amplifier gets inadvertently or deliberately turned up.

If you have the amplifiers flat out you just need to trim the level further back. This might be at the crossover or mixer. If you are adjusting the levels at the mixer there is still a possibility that you can turn the levels up too much. With this approach there is less chance of getting the relative levels between amplifiers wrong when setting up because you just wind them round as far as they will go.

Gain staging, whilst important, is not that critical. If you are operating your mixer within reasonable level limits and the PA is loud enough it doesn’t really matter where the levels on the amplifier are. If your mixer is constantly clipping and in the red yet your amplifiers are getting nowhere near clipping and it is not loud enough then you need to reassess your settings.

It doesn’t work the other way round. If your amplifiers are constantly clipping and your mixer is idling then PA is too small, no amount of fiddling with levels will make it loud enough.

If you didn’t already know, switch on the amplifiers last and turn them off first. If you turn on your amplifiers first and then say the mixer you get a loud clonk that doesn’t do loudspeakers any good.

[dboomer]

There are two schools of thought here and maybe the bigger point is ... if you don't have a problem with distortion nor with system hiss then there's really no need to change whatever you are doing now. You do however have the option to improve both of these.

Leaving the amps wide open can prevent anyone from changing your settings (for the worse) if you can control access to the gear.

Electronically there is an indisputable advantage to not turning the amps all the way up. Turning amps WFO typically results in the loss of 16-20 dB of dynamic range in your system.

Most mixers are capable of putting out +24 dB and even really big power amps typically can be driven to full power with about +8 or less. So straight away that's 16 dB that you paid for in your mixer that you can never actually use ... it's simply wasted.

[ears2thesky]

Electronically there is an indisputable advantage to not turning the amps all the way up. Turning amps WFO typically results in the loss of 16-20 dB of dynamic range in your system.

Most mixers are capable of putting out +24 dB and even really big power amps typically can be driven to full power with about +8 or less. So straight away that's 16 dB that you paid for in your mixer that you can never actually use ... it's simply wasted.

More newbie nonsense. In most every system the mixer will be going through various processors before hitting the amp. Therefore the mixer's output level vs the amp's input sensitivity is irrelevant. Amps are left wide open so that the amp's full gain range is accessible. Any attenuation of the signal is accomplished through processing.

Don't ever use terms like "indisputable" before you have a complete understanding of what you're talking about.

[dboomer]

Originally Posted by ears2thesky

Don't ever use terms like "indisputable" before you have a complete understanding of what you're talking about.

Well let's see .... I was part of the design team for a major manufacturer and probably have tens if not hundreds of thousands of amplifiers in the field. How about you?

The gain of 99.9999% of power amplifiers is fixed. The input sensitivity control knob does not change it. It only optimizes out the drive.

As far as the mixer going through other processors you are correct ... and each one of them must be balanced out for maximum performance.

[ears2thesky]

Well let's see .... I was part of the design team for a major manufacturer and probably have tens if not hundreds of thousands of amplifiers in the field. How about you?

I'm glad you have a solid theoretical basis for your many incorrect statements. However, when you've logged hundreds or thousands of hours in actual real-world jobs ranging from clubs, to theaters, to arenas I'll take your recommendations to heart.

Nothing personal, dude... it's just that I've seen many folks who make sweeping statements out of their asses just because they can sketch an amp schematic on a napkin. If you've worked very many professionally-run shows you would know that "99.9999%" of the time the amps are pinned.

[1vibes]

Hi Guys, my first post here and I have been trying to find some reinforcement info for this rageng battle I am having with a band member, "who owns the PA" over the amp settings. I have been performing for lets say a long long time and running sound systems just as long. I always crank my amp all the way up and run my master fader on the board at detente, the trims around 12 o,clock then raise the individual faders accordingly. I always have a clean sound with plenty of headroom.
Now this fellow has Mackie active speakers and runs the console faders all at detente and trims around 12 o,clock. he has the levels set just under clipping on all channels, as well as the masters, and runs the amps on the speakers less than half way up. I think we sound distorted and his wife is constntly running up on stage pushing up the faders and there is no where to go! When I tell him to pull down the individual faders and crank up the amps so we have some head room it is just a fight and useless. I can't believe someone can be so stubborn as to think this is correct. but he got his info from a friend who went to full sail. lol His friend told him about gain stage and that is fine but he just doesn't get that you have to turn up the amps and pull down the faders after you set the gain stage. Am I crazy or ??? I mean the faders set at detente with the individual channel reading just below clipping. I have never had a mix that set straight across the board with no headroom and power amps up less than half way or halfway at the most. I say crank up the amps and then mix the console accordingly. What say you? Also the majority of venues are outside.

[Steve_B]

As dboomer said, most power amplifiers have a fixed gain. The knob on the front is usually an attenuator, altering the level before it goes through the fixed gain.

I’ll assume that by 99.9999% of the time the amps are pinned, you are implying that the amps always on the point of clipping, and that the rest of the system is not clipping.

Forget any complications of intermediary gear between the mixer and the amplifier. Say that with the amplifier controls wide open it only requires a signal from the mixer which is 30dB below the mixers clip point to achieve full power. That is 30dB of useless headroom in the mixer. You can’t use it because the amplifier is clipping.

If the noise floor of the mixer is at 80dB below its clipping point that sets your dynamic range at 50dB. At -80dB you are below the noise floor and at -30dB you are clipping the amplifier.

If you attenuate the signal at the amplifier by 20dB you now need to turn up the mixer to 10dB below clipping to get maximum output. If the noise floor is still at 80dB below clipping you now have a dynamic range of 70dB.

Mixers have more than one gain stage and you can’t just dismiss gear downstream of the mixer, so in reality things are more complex. Hopefully the people who can sketch a circuit on the back of a napkin have done their work properly and optimised the performance of the electronic gear.

With most modern equipment there is a lot of leeway before you get to the point where things get noticeably wrong.

[dboomer]

Originally Posted by ears2thesky

I'm glad you have a solid theoretical basis for your many incorrect statements. However, when you've logged hundreds or thousands of hours in actual real-world jobs ranging from clubs, to theaters, to arenas I'll take your recommendations to heart.

Paid plenty of dues, thank you. But being a "professional" is not the same thing as being an "expert". You should probably do a little research and see what the "experts" in the field recommend.

If you've worked very many professionally-run shows you would know that "99.9999%" of the time the amps are pinned.

Just so we're on the same page ... by "pinned" do you mean with the sensitivity knob turned up, wide open? I agree that you see this done frequently ... but ... there could be improvement to the dynamic range of that system by turning them down as laid out in Steve B's explanation. Once you have driven the power amp to full output and still have 15-20 dB of headroom left in your mixer, that headroom is completely wasted. You paid for it and have thrown it away.

[dboomer]

Originally Posted by 1vibes

I always crank my amp all the way up and run my master fader on the board at detente, the trims around 12 o,clock

This may work well for you and you may have no problems ... but it could be better.

The relative positions of the knobs don't really mean much and terms like "unity gain" also don't mean much ... unless you have a calibrated system and trust me you don't have a calibrated system when the amps are wide open. The meters on your board hopefully are calibrated but only in relation to the mixer. Your meters could be in the green and yet you could be clipping something else and/or blowing up speakers ... you just have no meaningful reference at this point.

However when you set the clip level of your board to reflect the clipping (or limiting) point of your amp now your meters will tell you how much you have left in your system ... not just your mixer.

[Steve_B]

One could get philosophical and pedantic about this. It is only headroom if you don’t use it. So if you don’t want to waste the headroom you have to turn down.

Perhaps this is why people think it is best to run with the amps turned up full. Your mixer has more headroom so it must sound better.

Having a meaningful reference point can’t be overstressed either. Knowing what your amplifiers are doing by looking at your mixer output meters is to me important.

One reason given for running the amps at full is that it stops other users pushing the mixer into the red (which would obviously catastrophic). I have found the opposite to be mostly true. Those of us who are in the know, , know you don’t get too far in the red; not like them crazy djs . Psychologically we tend to not push past the 0dB -+3dB level on the mixer. Turning the amps down is an effective way of reducing the power going to your speakers. Relying on limiters might reduce the peak power but can result in increased average power levels.

In the end, it is not that critical, and to repeat what has been said already, if you have a system that works for you stick to it.