Power amp level setting: Xstatic or other experts - I need advice

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gecko zzed

gecko zzed

Grumpy Mod
For years I (and other live sound engineers who I associate with) have operated a rig by running power amps fully wound up.

In my recent reading on this topic, I am now given to believe that this is not in fact the best way of setting up a system.

My usual practice (in brief) is to:

a) wind amps up
b) set desk master fader to unity
c) set input channel gain to get a PFL level of around unity
d) bring channel fader up to taste.

My recent reading suggests an alternative

a) set input gain to get PFL level of around unity
b) set channel fader to unity
c) set desk master fader to unity
d) bring power amps to taste

Can anyone offer advice on either of these techniques, and why one would be preferable to another?
 
There are many factors involved in how you set your amps. Generally, I run all amps at full as do most professionals. However, if you have a lot more PA then necessary, this can lead to a master fader level that is way too loud when set at unity. Personally, I would just drop the master fader a little and leave the headroom at your amplifier. Its important to remember that the quickest way to blow your speakers is by overdriving your amplifier and squaring your speakers. If your amps are at full, you are much less likely to do this. As far as PFL goes, setting your PFL level to average around 0 is a good idea. This is what most all console manufacturers build in as the optimal level for noise and frequency response of their preamps and the rest of the channel circuit (aux sends, EQ). The biggest advanttage of running a fader at unity is the logarithmic nature of the faders themselves in my opinion. Averaging around unity means that a move of half an inch or so on a 100mm fader is only 2 or 3 db in volume which means you can accurately make minor changes. If however your fader is at the bottom of the fader path, a move of half an inch can result in a 20 or 30 db swing sometimes which makes it really hard to make a small change.

In the end, a lot of these decisions are kind of a personal choice. Here is what I have noticed after working with 100's of engineers over the years. Most all of the guys that I have worked with that unitied all of the faders and fussed about amp volumes and master fader levels put out stale sounding mixes that just didn't sound very good. The engineers that found the sweet spots for everything and just used there ears instead of scientifically relying on PFL levels and having everything at unity, tend to get bigger wider sounding mixes that sounded much better. I understand that this is not ALWAYS the case and that every engineer is different, but the reality of the situation is that at least 9 out of 10 of my experiences with many many engineers have turned out this way. This is also why I don't hire anyone who went to school for this stuff. Sometimes what we learn in school and what needs to happen in the real world are not always the same. Sound can be a science, but it can be an art too. I know which one I choose ;)
 
xstatic said:
There are many factors involved in how you set your amps. Generally, I run all amps at full as do most professionals. However, if you have a lot more PA then necessary, this can lead to a master fader level that is way too loud when set at unity. Personally, I would just drop the master fader a little and leave the headroom at your amplifier. Its important to remember that the quickest way to blow your speakers is by overdriving your amplifier and squaring your speakers. If your amps are at full, you are much less likely to do this. As far as PFL goes, setting your PFL level to average around 0 is a good idea. This is what most all console manufacturers build in as the optimal level for noise and frequency response of their preamps and the rest of the channel circuit (aux sends, EQ). The biggest advanttage of running a fader at unity is the logarithmic nature of the faders themselves in my opinion. Averaging around unity means that a move of half an inch or so on a 100mm fader is only 2 or 3 db in volume which means you can accurately make minor changes. If however your fader is at the bottom of the fader path, a move of half an inch can result in a 20 or 30 db swing sometimes which makes it really hard to make a small change.
Click to expand...

Thanks Xstatic. I am mighty grateful for your quick and thoughtful reply.

What you've written there is what I had learned over the years, and seems to be intuitively correct.

I recall once having to run my desk with an in-house system that had so much power that, with amps wound full up, I had virtually no control over the desk . .. every fader was near the bottom of its path. That, and other similar circumstances are the only times I've felt the need not to wind the amps fully up.
 
Cranked

I run my amps with the setting set to max.

Reason is I run a digital speaker processor before the amps. (EV DC-One )
Feeding 3 amps Hi's, mids and lows
I adjust with the main on the mixing board.

The reason is the amp rack is on stage near the speakers
 
Thanks.

It just seems logically right to do it this way. I feel more comforted now. But I'd be interested in learning the rationale for the other. I note that Yamaha and Rane recommend it, but I'm not satisfied with how they explain it.
 
Slightly off topic but would you guys use the same approach for an amplifier that is powering a set of studio monitors? I guess I never researched it but I usually run my monitor power amp at about 1 o'clock on the left and right channels. Probably a bad assumption but I just assumed going full volume on the power amp was a bad idea. Looking back now, I see that I had no real reasoning behind it lol.
 
Ok apparently my memory isn't so good. I went ahead and cranked the volume on my power amp and I was suddenly reminded that my cheap EMU soundcard that I use for general computer listening gets pretty noisy. I can't hear the little pops and clicks if I keep the power amp at a reasonable volume DUH!
 
Thanks for the helpful comments, everyone.

I would be interested in your take on this article:

www.gain.pe.kr/spboard/board.cgi?id=audio&action=download&gul=14

The author is a guy called Chuck McGregor, and he describes a way of optimising a system's gain structure. This is being hailed by some people as being the 'only way' to set up a PA. I beg to differ, but I'm not winning. I think that what Chuck says makes sense, but I'm not sure how widely the method is used . . . more importantly, I'm not sure how 'needed' the method is.
 
Chuck's method is indeed the way to maximize your dynamic range. Notice he says nothing about how hot to run your inputs or anything like that. His method is strictly about getting the most dynamic range and best s/n ratio out of your gear. What you do with it after that is up to you.
 
I would always run the power amps at max. Then trim all the levels from the inputs and any processing (gain, eq, compression, etc) before the amps to the correct no clipping levels. I would rather gain down before the amps than push the gain to a turned down amp.

I would also have amps that were rated at least twice the speaker rating to prevent square waving the amps, the square wave is what blows speakers quickest. Most speaker ratings (good brands with correct rating) are for rms and will handle peaks at twice that rating anyway. Use your ears, speakers will let you know when they are under stress.

Cheers

Alan.
 
witzendoz said:
I would always run the power amps at max. Then trim all the levels from the inputs and any processing (gain, eq, compression, etc) before the amps to the correct no clipping levels. I would rather gain down before the amps than push the gain to a turned down amp.
Click to expand...

thanks Alan

that's the way I do it, and it's what feels intuitively 'right'
 
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