Maxing out power amps..??

LightGroove · #1 08-02-2010, 10:08 PM

Ive been in this constant struggle with our guitard and hoping to find some balance. He is convinced that the only way to have good sound to is crank everything...go figure. Im of the school of thought of using only what you need..in my case about 60-70% of the amp...At this rate we still have a ton of headroom and dont see any point in cranking.

He is so convinced that he invited another sound guy out to practice tonight to do his magic. For some reason our sound was always so dull and lifeless to the guitard....after this guy worked his magic..it came alive and sounded better then ever..

His magic..cranking our amp....

He stated this was the only way for things to sound good and to avoid ruining the amp.

So am I crazy for backing off?

somegeezer · #2 08-02-2010, 10:10 PM

Fire him and let him and his soundman go make full crank love in their own time. For a start, it's only a practise. You need even less volume there than on stage. It's a wonder you guys don't go deaf instantly.

GregShadoan · #3 08-02-2010, 11:21 PM

No, we (sound people) run PA amps on full all the time. Attenuation to the amps is done on the DSP, or crossover. Once is a blue moon a monitor guy will like to turn down the horn amps a little, maybe 10 percent, but the FOH amps are always full on. We have about 25 crown macrotechs that just get turned on, and off. We don't touch the knobs. YMMV. Its a fairly medium size PA though. 16 boxes. 3 way, with 10 bi-amped monitor mixes, and 3 way sidefills.

TimmyP · #4 08-03-2010, 01:58 AM

So long as nothing is clipping, it does not matter all that much. However I always run amps wide open. Otherwise, when they are inadvertently (or with malicious intent) turned up, the system limiters will no longer do their job.

jtc_hunter · #5 08-03-2010, 07:38 AM

I think it is important here to specify to the OP that ,Yes, you are running the power amps wide open, but the individual channels are NOT run wide open, therefore an individual guitar, bass, mic, etc, is not totally cranked wide open balls to the wall. Running a power amp wide open with channels adjusted down to moderation is like running a guitar or bass amps Gain wide open , but Master turned down to taste.

GregShadoan · #6 08-03-2010, 08:03 AM

Ok sure. The power amps are the only thing in a PA system that are full on. Everything else is tuned for proper gain structure.

R. Laevinus · #7 08-03-2010, 08:10 AM

Quote:

Originally Posted by GregShadoan

Ok sure. The power amps are the only thing in a PA system that are full on. Everything else is tuned for proper gain structure.

Then you're fine.

Wes Whitmore · #8 08-03-2010, 09:32 AM

Quote:

Originally Posted by GregShadoan

Ok sure. The power amps are the only thing in a PA system that are full on. Everything else is tuned for proper gain structure.

We PFL each of our inputs and adjust the input trim on each strip until that input is hitting 0 (unity). We go across each input and do this. Then, we bring up the main outs (with amps gain all the way down), and raise that to 0. Then we set any equipment between tha mixer and amp the same way. We adjust the "sensitivity" knobs on the amp up until we are putting out the amount of voltage to our speakers that we are targeting. We also know that the clip point is much higher that we are currently at giving our input voltage. We then tell our soundman to keep the channel strips below 0, the mixer master below 0, and to try not to boost the EQ (cut instead). It stays nice and clean and sounds like a much bigger system than it is.

Wes

WayneP · #9 08-03-2010, 11:06 AM

Excellent article on gain structure:
http://www.rane.com/note135.html

Regards,
Wayne A. Pflughaupt

Pedulla Club #45

Zooberwerx · #10 08-03-2010, 12:29 PM

The attenuators on my QSC RMX stuff are set @ 20-25. I use the dbx procedure (and a pink noise CD!) to adjust gain(s), establish headroom, and set limiters. Its a one time deal and you're good to go. Also provides the best signal / noise ratio and no clipping whatsoever. FWIW, this is a PA application.

Riis

LightGroove · #11 08-03-2010, 01:55 PM

So Riis...are you saying that your amp isnt totally maxed out?

Im familiar with gain structure and unity and the ideal zone. The distortion end of things is what concerned me along with pushing at maxed output when it was unnecessary. I guess in a nutshell I want maximum headroom with maximum signal to noise.

example...at a recent show I had our main power amp ( 500w x2 4ohms) going to our 2 main speakers....I had the amps at about 75% of full power. After going through the gain structure and such I couldnt push things past about a 3 or 1/4 of the way before the audience was holding their ears. Granted they were close but still...no where close to unity or 0 in the main level

So my mind thinks that pushing the amp back to 50% and then pushing the master closer to 0 makes more sense.

GregShadoan · #12 08-03-2010, 04:35 PM

Quote:

Originally Posted by LightGroove

So Riis...are you saying that your amp isnt totally maxed out?

Im familiar with gain structure and unity and the ideal zone. The distortion end of things is what concerned me along with pushing at maxed output when it was unnecessary. I guess in a nutshell I want maximum headroom with maximum signal to noise.

example...at a recent show I had our main power amp ( 500w x2 4ohms) going to our 2 main speakers....I had the amps at about 75% of full power. After going through the gain structure and such I couldnt push things past about a 3 or 1/4 of the way before the audience was holding their ears. Granted they were close but still...no where close to unity or 0 in the main level

So my mind thinks that pushing the amp back to 50% and then pushing the master closer to 0 makes more sense.

Umm, no you had the amps at full power, you had the input attenuation at 75%. That means you were driving the signal path too hard before the amps.

Zooberwerx · #13 08-03-2010, 06:29 PM

Quote:

Originally Posted by LightGroove

So Riis...are you saying that your amp isnt totally maxed out?

Im familiar with gain structure and unity and the ideal zone. The distortion end of things is what concerned me along with pushing at maxed output when it was unnecessary. I guess in a nutshell I want maximum headroom with maximum signal to noise.

example...at a recent show I had our main power amp ( 500w x2 4ohms) going to our 2 main speakers....I had the amps at about 75% of full power. After going through the gain structure and such I couldnt push things past about a 3 or 1/4 of the way before the audience was holding their ears. Granted they were close but still...no where close to unity or 0 in the main level

So my mind thinks that pushing the amp back to 50% and then pushing the master closer to 0 makes more sense.

Any amp is capable of pushing its full power irrespective of attenuation...all it needs is a hot enough signal. The key is identifying where your PA mixer clips, where your amps clip, setting sub-clip thresholds, and applying limiters appropriately. As it stands, I have something like 15-17 db of headroom, plenty of low-noise volume, and no clipping.

In days of yore, we used to turn all attenuators to -0- and be done with it. However, when you push the master sliders up 1/2 way, its red light / clip city. If you're running an external limiter, go ahead and dial it in. Problem is you end up with about 5 db of headroom and lots of background noise.

Riis

LightGroove · #14 08-03-2010, 08:29 PM

Quote:

Originally Posted by GregShadoan

Umm, no you had the amps at full power, you had the input attenuation at 75%. That means you were driving the signal path too hard before the amps.

After reading the link earlier in the thread I have a better understanding of the amp itself...I now realize the knob I was associating with creating more juice is more of an attenuation knob .

I think I may have mistyped . After looking at the board the master or main out sliders are pushed between the -20 and -12 mark...which from bottom to top is only about 1/4 of the way up....basically im barely pushing anything and its crazy loud.

This is where Im confused in trying to find the balance or best signal. As an example..Channel 1 is my main vocal mic. Ive got the gain set just short of clipping and the slider set at unity. Now my mains as stated earlier are barely being pushed. Is the idea to have these main sliders closer to the top so the amp is getting maximum signal? or should I leave things as is?

I guess my main question is...should I get the board set and have everything cranked , then slowly turn the main amp knobs until I reach a specific point?

countrybass007 · #15 08-03-2010, 08:34 PM

I was told years ago that the power amps run cooler and are more efficient when they are wide open. The actual volume levels are then controlled on the board.

GregShadoan · #16 08-03-2010, 08:38 PM

Yes. Don't pay to much attention to the Mackie manuals, that say you have to run all your channels to zero to start. Most of the time much less is required. If you run your channel nearly into clip, I would say it's too hot. Let the PA do the work, don't dime the channels. That's where clipping starts :-) On one of my consoles, (an old Ramsa SX-1) good gain on a channel PFL is about -7 or so. Anymore and things get ugly.

GregShadoan · #17 08-03-2010, 08:40 PM

Quote:

Originally Posted by countrybass007

I was told years ago that the power amps run cooler and are more efficient when they are wide open. The actual volume levels are then controlled on the board.

I agree with that statement.

walterw · #18 08-03-2010, 09:39 PM

Quote:

Originally Posted by countrybass007

I was told years ago that the power amps run cooler and are more efficient when they are wide open. The actual volume levels are then controlled on the board.

Quote:

Originally Posted by GregShadoan

I agree with that statement.

well then sorry, because it's totally false.

an amp runs as efficiently as its ratio of power sucked out of the wall to power pushed into the speakers.

it runs as cool as its cooling fans will manage for however hard it's working.

the knobs on the front of the amp have nothing to do with either.

i dime my PA amps so i don't have to go running over to them to turn them up in the middle of a show because the rest of the system is clipping before the volume is right. someone else with a different system might need to turn the amps down to keep from blowing up the club with the mixer barely cracked open.

as long as the whole signal chain isn't being pushed too hard or is barely on, and the amps aren't peaking too much, whatever works is fine.

GregShadoan · #19 08-03-2010, 10:55 PM

Quote:

Originally Posted by walterw

well then sorry, because it's totally false.

an amp runs as efficiently as its ratio of power sucked out of the wall to power pushed into the speakers.

it runs as cool as its cooling fans will manage for however hard it's working.

the knobs on the front of the amp have nothing to do with either.

i dime my PA amps so i don't have to go running over to them to turn them up in the middle of a show because the rest of the system is clipping before the volume is right. someone else with a different system might need to turn the amps down to keep from blowing up the club with the mixer barely cracked open.

as long as the whole signal chain isn't being pushed too hard or is barely on, and the amps aren't peaking too much, whatever works is fine.

Ok Walter, fair enough, I guess I was thinking more in terms of the latter part of the statement :
"The actual volume levels are then controlled on the board."
more than the run cooler and more efficient thing.
I stand corrected.
You are right.
G

Zooberwerx · #20 08-04-2010, 06:01 AM

Channel / master sliders = volume control

Amp attenuators = gain structure / "matching" components

If adjusted properly beforehand, its pretty much a "set it 'n forget it" situation. This provides a quasi-linear response / relationship amongst the components and eliminates the need to constantly tweak attenuators up & down....particularly bothersome in a live performance setting. FWIW, I can use our full-blown gig rig and play canned polka tracks for the folks at Westminster Canterbury without changing any parameters with the exception of the master slider. OTOH, these folks are deaf to start with.

Riis