Why Are Knobs on Power Amps Turned all the Way Up?

[Big Al]

Both sound guys I've worked with kept the knobs on their power amps at 100%. Why do they do this? Is it so they won't have to climb up on stage to adjust them during a gig? Does it have something to do with gain structure? Does a source sound cleaner if it goes through as little gain as possible at the board?

 

It seems like a lot of effects and other musical stuff is designed to perform best with the knobs at 12:00. Are power amps different?

[kevinnem]

it is best not to think of them not as "turned up" but and "not turned down"

 

Full open is 0 and anything less is a negitive number.

 

In genral I think the best argument is that if you start full up. people can only go downward on you. a surpise of something being less loud, is usally better then something being louder.

[alteredsound]

Chances are, they feel they need all the power the amps can give them to get to the output level they want to run at. If the gain is turned down on the amps, then you have to send a higher output level from the mixer to achieve the same output levels that you had with the gain all the way up. When this happens, you risk your output signal clipping coming out of the mixer.

 

If you aren't trying to run the system at its full capacity (for example, playing in a small room where your system is way more than is needed for the room) then you can turn down the gain on the amps and still run near unity on your mixer. Some people think certain amps sound better if they aren't wide open.

[Big Al]

 

If you aren't trying to run the system at its full capacity (for example, playing in a small room where your system is way more than is needed for the room) then you can turn down the gain on the amps and still run near unity on your mixer. Some people think certain amps sound better if they aren't wide open.

 

 

That kind of describes how I run amps in our practice room or when I run our monitors. The question is, which end do you start from? I've always started with mic trims at 12:00, faders at what I guess is called "unity", etc. Then the master fader is at or below unity (if that's the right term). I put the power amps between 12:00 and 2:00 depending on how loud it needs to be. If the power amps are at full power, do you start with your master fader at unity and then work backwards from there, next setting the channel fader and then adjusting the trim? It this what people call "gain structure"? Sorry for the noob questions. Thanks for your help.

[Gregidon]

 

Both sound guys I've worked with kept the knobs on their power amps at 100%. Why do they do this? Is it so they won't have to climb up on stage to adjust them during a gig? Does it have something to do with gain structure? Does a source sound cleaner if it goes through as little gain as possible at the board? It seems like a lot of effects and other musical stuff is designed to perform best with the knobs at 12:00. Are power amps different?

 

 

1) To keep people from messing with the knobs when they think it should be louder.

2) Gain structure - This is usually not optimal, but it's good enough when you take into account 1).

3) Best SNR is achieved with higher output from board, again see 1).

 

Side note, for some amps you can get security covers to prevent people from messing with them. This can be a great help to keep the "helpers" at bay and maintain proper gain structure. My first amp (a QSC 1400) had the knobs on the back which accomplished pretty much the same thing.

[Scodiddly]

Plus it's easier to maintain proper balance between things - all the way up is always all the way up. Trying to consistently set knobs at some partial is likely to result in some amps being a few dB different from others.

 

The only exception we have at work is with some biamped speakers where we're turning down the treble channel "5 clicks below full-on".

[alteredsound]

 

That kind of describes how I run amps in our practice room or when I run our monitors. The question is, which end do you start from? I've always started with mic trims at 12:00, faders at what I guess is called "unity", etc. Then the master fader is at or below unity (if that's the right term). I put the power amps between 12:00 and 2:00 depending on how loud it needs to be. If the power amps are at full power, do you start with your master fader at unity and then work backwards from there, next setting the channel fader and then adjusting the trim? It this what people call "gain structure"? Sorry for the noob questions. Thanks for your help.

 

 

Here's something from a mixer manual about system setup.

 

To get the best performance from your system, it is important that you set up the gain structure correctly within the console and also within and between the connected equipment. Ideally, each circuit should be set to clip at the same time if the signal became too hot, in other

words each would have similar headroom relative to its nominal operating level. The resulting dynamic range is the difference between the highest noise floor and the lowest headroom through the system. The performance is only as good as the weakest link.

 

Use the channel meters and PFL/AFL system to set the gains and mix levels to average around

[alteredsound]

Here's another section from it that may help answer some of the questions you asked too.

 

There is a technique used by some operators where they set all the faders to

[Big Al]

 

Here's another section from it that may help answer some of the questions you asked too.   There is a technique used by some operators where they set all the faders to

[Eric_the_mixer]

 

YES!! Everything you posted is right on the money. Our sound guy sets the faders at 0 and uses the trims to adjust the volume. It's not a bad idea during soundcheck, but when he touches the trims during a gig, all hell breaks loose. That's why I started running our monitors. The monitors would sound fine during soundcheck, but once he touched the trims, we'd get feedback or I wouldn't be able to hear myself. It sounds like I'm setting things up the right way...

 

 

You are more right than your sound guy, but simply setting each mic preamp to 12 o'clock is not the way to do it either.

 

Typically, each mic is on a different source. Each source makes a different sound with different dynamics and therefore requires a custom gain structure. Also consider that different mics are more or less sensitive, which means they require a different mic preamp setting.

[xmlguy]

with my beer on top.

 

[stunningbabe]

 

You are more right than your sound guy, but simply setting each mic preamp to 12 o'clock is not the way to do it either. Typically, each mic is on a different source. Each source makes a different sound with different dynamics and therefore requires a custom gain structure. Also consider that different mics are more or less sensitive, which means they require a different mic preamp setting.

 

 

I agree totally. Each musician is also different in volume, tone and playing character. There's no hard rules about it.

[Mogwix]

 

I've always started with mic trims at 12:00, faders at what I guess is called "unity", etc. Then the master fader is at or below unity (if that's the right term).

 

Here's how my gain structure is set:

 

1) Turn everything to zero on the mixer, EQ and pan at 12 o'clock. Amp "attenuators" at full.

 

2) Hit the PFL and get signal from your source(s), increase the preamp gain until you have ample signal, but not too much or you risk clipping the preamp. Make sure the loudest signal from the source(s) is safely below clip.

 

3) Bring your master fader to 0

 

4) Bring channel faders up to where you want them. If you're pushing them above 0 then consider either pushing the master fader up, but if your amps are properly sized for the speakers you're using, then bringing up the master to get more headroom out of your channels probably means you're pushing the PA too hard. Watch for flashing red lights on your amps! It's fine to push a PA a little, they're designed with tolerances to deal with that, just don't push it too hard. If you're consistently pushing your rig, maybe it's time for an upgrade.

 

Mixing with the gain pots is ridiculous IMO, too much risk of clipping the preamps (I have SD condensers that clip the pre's if I don't have them on 0, and that's with a pad!), and the other points of SNR and monitor levels.

[Big Al]

 

You are more right than your sound guy, but simply setting each mic preamp to 12 o'clock is not the way to do it either. Typically, each mic is on a different source. Each source makes a different sound with different dynamics and therefore requires a custom gain structure. Also consider that different mics are more or less sensitive, which means they require a different mic preamp setting.

 

 

Yes, I agree--12:00 is just a starting point. I think I'm doing it right. It sounds like it's better to get your mixer set up properly and then worry about your amp volume than it is to crank your amp up all the way and back into the levels on the mixer. Nobody is going to touch my amp kobs but me, and leaving a little headroom allows me to turn them up a hair later if I need to. Also, I'm just running 4 identical speakers set up as 4 monitors or 2 monitors and 2 mains. In a more complicated setup with more than one amp, there could be an advantage to knowing the amps are at the same level. It sounds like none of the advantages of starting with amps at full power really apply to my setup, and I've spent hours tweaking it in various rooms. I've got a pretty good idea of how the rig sounds best.

[twostone]

Guess if I was using 100 different mixer at once then I would have a amp WFO:eek: but just the one mixer I got puts out plenty of signal on my amp.

[moody]

 

Yes, I agree--12:00 is just a starting point. I think I'm doing it right. It sounds like it's better to get your mixer set up properly and then worry about your amp volume than it is to crank your amp up all the way and back into the levels on the mixer. Nobody is going to touch my amp kobs but me, and leaving a little headroom allows me to turn them up a hair later if I need to. Also, I'm just running 4 identical speakers set up as 4 monitors or 2 monitors and 2 mains. In a more complicated setup with more than one amp, there could be an advantage to knowing the amps are at the same level. It sounds like none of the advantages of starting with amps at full power really apply to my setup, and I've spent hours tweaking it in various rooms. I've got a pretty good idea of how the rig sounds best.

 

 

You can't think of a power amplifier like that. Whether set on full or slightly down they are not something that you should change to get a little bit more power - that's what your mixer is for.

[xmlguy]

Why? To get them all the way to 11, of course. Not much good having an 11 if you don't use it, innit? It's one louder, you see.

[W. M. Hellinger]

Let me ask this:

 

Do you keep a stack of cards under the gas pedal of your automobile, and then add or subtract cards from the stack based on how fast you think you'll need to go somewhere?

[drumstix]

Here's how my gain structure is set: 1) Turn everything to zero on the mixer, EQ and pan at 12 o'clock. Amp "attenuators" at full. 2) Hit the PFL and get signal from your source(s), increase the preamp gain until you have ample signal, but not too much or you risk clipping the preamp. Make sure the loudest signal from the source(s) is safely below clip. 3) Bring your master fader to 0 4) Bring channel faders up to where you want them. If you're pushing them above 0 then consider either pushing the master fader up, but if your amps are properly sized for the speakers you're using, then bringing up the master to get more headroom out of your channels probably means you're pushing the PA too hard. Watch for flashing red lights on your amps! It's fine to push a PA a little, they're designed with tolerances to deal with that, just don't push it too hard. If you're consistently pushing your rig, maybe it's time for an upgrade. Mixing with the gain pots is ridiculous IMO, too much risk of clipping the preamps (I have SD condensers that clip the pre's if I don't have them on 0, and that's with a pad!), and the other points of SNR and monitor levels.

 

 

 

 

+1 exactly!

 

 

I had a studio engineer (if he could be called that) mix for us a few times as an acting manager. I would set up the band, monitors, FOH and then jump behind the drums. Mr engineer would decide to make a few minor adjustments druing the gig and use the channel strip gains for the adjustment. Man did he screw up the monitors!

[Scodiddly]

Let me ask this: Do you keep a stack of cards under the gas pedal of your automobile, and then add or subtract cards from the stack based on how fast you think you'll need to go somewhere?

 

[fmw]

The purpose of the volume pots is to balance the channels with each other for stereo, not to control volume. You control volume at the mixer. If the channels don'

t need balancing, there is no point in turning down the potential output of the amps when you control it elsewhere.

[stunningbabe]

Let me ask this: Do you keep a stack of cards under the gas pedal of your automobile, and then add or subtract cards from the stack based on how fast you think you'll need to go somewhere?

 

[stunningbabe]

The power amp always gives out the same rated output whether you put the volume knob at 5 o'clock or 10o'clock. It's the Mixer that controls the rest.

[Big Al]

I see what you guys are saying, especially as it applies to running FOH or running FOH and mixers from the board. However, I can still see some advantages to the way I've been doing it (I mainly run monitors). Sometimes it's nice to be able to adjust a monitor's overall volume on the fly when it's getting the same mix as a monitor that you don't want to change. Also, we normally play small bars, so the monitors don't need to be pushed at all. If they get too loud, you get a loudness war, and the sound guy has no control over the FOH mix.

[Phil Clark]

We always run our amps full open, and that way if someone gets to the amp rack and starts fiddling with the nobs, the worst they can do is turn things down.

 

Don't think it happens? We played a block party one year and all of the sudden the sound changed, and I thought that one of the amps went into protect mode. When I went to check it, I found that someone walking by the rack had reached over and turned a knob, turning the mids down on one side of a stereo stack (we run our rig in stereo, but mix in mono except for the keys which sometimes need stereo for the Hammond B3 patch).

 

If we ran at less then full on, and the knob had been turned the other way... I shudder to think of all the bad things that could have happened then.

 

Since that show we now set the amps on stage so that no one can get to the knobs.