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full Volume on power Amp?

#42
Just to clarify, 1 o'clock (while different for everyone) is just more than the middle of the pot. For me, this provides ample headroom and security. I never put a poweramp above 4:00 to assure that I won't blow the speakers (I keep a limiter on all incoming audio as well). I control the main volume with the preamp, and if I need tons more sound, I crank the poweramp from 1 to 4. But I suppose too that it changes if you use tubes or not....
 
#44
ajota_di said:
Just to clarify, 1 o'clock (while different for everyone) is just more than the middle of the pot. For me, this provides ample headroom and security. I never put a poweramp above 4:00 to assure that I won't blow the speakers (I keep a limiter on all incoming audio as well). I control the main volume with the preamp, and if I need tons more sound, I crank the poweramp from 1 to 4. But I suppose too that it changes if you use tubes or not....
Click to expand...
come again?
 
#47
Jazzdogg said:
Debate?

I saw someone bring a butter knife to a gun fight and withdraw with appropriate alacrity and humility.

KUDOS to Bob Lee for handling the exchange with detached professionalism.
Click to expand...

Ouch! I was going to sit out...

We've been swinging the "big clean power = safe, small clipped power = not safe" butter knife for hundreds of interested parties per year for about 40 years. Nobody had ever called us back and said "you were wrong", but lots have admitted we were right. Anecdotal? Yep, but that's lot's of thousands of anecdotes.

I posted my considered opinion on the matter, and would be happy to back the anecdotal evidence with some science, if someone wants to send me, say, around 10 identical, high quality drivers that they don't want back...

Edit: I should point out as well, that I've spend the last 15 years doing design, testing and tech support for another North American amp manufacturer, and while our butter knife isn't as big as QSC's, we do keep it sharp. However, I'm on this forum because I'm a bassist, so with respect to all,

Later, and thanks for your patience with my crazy opinions...

Edit: Holy Crap! Just actually looked, and realized I was arguing with the secretary of the AES. I'm going to get my arse kicked on Monday...

Bob, please accept my humble apologies, and I'm sure we probably agree on 99% of this stuff.
 
#50
Gawr, I need to stop posting at midnight... Okay. I keep my poweramp at 1:00. This isn't pushing the poweramp too far, and ensures that (along with a limiter), the signal won't blow the speakers (assuming that they're appropriately matched...) and you'll have optimal headroom. IMHO, if you need to crank the power amp past 3:00 to be loud enough, you need to get another cab or a new poweramp. As far as pre amps go, I don't like cranking mine more than needed.... Being tube, it distorts when they're really pushed.
As far as live sound goes, I never turn the poweramp's volume. Always on the mixer. Always.
Sorry if I don't make any sense at all....
 
#51
Gain structure. Ask any good Sound Engineer about gain structure. Don't run the power amp wide-open unless you really need to, and in _some_ cases you may need to do exactly that. Attempt to balance the amount of gain (volume setting) at each step in your system, including pedals, etc, for the best signal-to-noise ratio and the best sound. This will vary depending on how and where in the chain you may want to intentionally create distortion.
 
#52
Downunderwonder said:
I need a facepalm stat.:o

All this time I've been faithfully boosting up my preamp to just before clipping and controlling volume with the power amp.

Yeah, listen to Bob, he's probably awake when he posts.
Click to expand...

I thought we were referring to separate preamp/ power amp setups? So your preamp should have a pre gain to set level and a master to control your volume, right? The power amp is the fuel for your fire. So when I used a pre/ power set up I set the pre gain level just below clipping, controlled the overall volume with the master and dimed out the volume on my poweramps so I get maximum headroom from my poweramp. I mean I can't be reaching behind my rack during a song, turning up my poweramps volume when I need to get slightly louder, can I?
I have done this for years and never blown any speakers. My personal method for achieving maximum head room out of my poweramp. Am I wrong?
 
#53
IMO, this discussion is better illustrated by the relationship between a mixer and power amps whereas we identify the clip points of both and establish a quasi-linear relationship. This practice provides improved signal / noise ratio, greater headroom, and no clipping.

Take a look at this dbx manual starting at page 37 / System Set-up and Gain Structure.

ftp://ftp.dbxpro.com/pub/PDFs/Manuals/English/DriveRack_PA_Plus_Manual_18-0483V-B.pdf

Granted, the references are specific for a dbx component but the principles can be applied to just about any sound reinforcement system. Anecdotally, the first time I set up my system, one of the initial instructions was "roll your attenuators back to 37% (11:00)". Say what?!?

Riis
 
#54
MVPBASS said:
So when I used a pre/ power set up I set the pre gain level just below clipping, controlled the overall volume with the master and dimed out the volume on my poweramps so I get maximum headroom from my poweramp. I mean I can't be reaching behind my rack during a song, turning up my poweramps volume when I need to get slightly louder, can I?
I have done this for years and never blown any speakers. My personal method for achieving maximum head room out of my poweramp. Am I wrong?
Click to expand...

Actually, this may result in diminished headroom. The problem is that there is all-too-frequently no indication of signal strength / clip on the pre's master volume. Sidenote: I believe my GK 2001 RBP has such an indicator....I'll check the manual. Here's an interesting experiment you can do on your own:

*Disconnect your speakers first!
*Dime your power amp attenuators. Defeat any onboard clip / limiter functions, too...these will blunt the amp's response. You can roll them back in when done.
*While playing, slowly turn up the pre's master volume until the power amp begins to "red light".
*Make a note of the pre's volume setting. Repeat the procedure using lower attenuator settings.

Could be your set-up is spot on. It still makes for an interesting exercise to see the interaction between the components.

Edit: Starting to sound like a broken record, but...any power amp, irrespective of attenuator settings, is capable of producing full output power if provided with a hot enough signal. The difficulty is establishing an optimal signal > output partnership.

Riis
 
#56
MVPBASS said:
My pre had an indicator light for gain. I have always used power amps with more power than I needed so I'd never have to push my speakers or amp too hard.
Click to expand...

Same here. Try the procedure in my previous post. It's a ton 'o fun! I use a more complicated procedure when setting up or mod'ing our FOH PA. It requires a CD player and "pink noise" CD and some of the DriveRack features including limiters. Which leads us back to your earlier post re: headroom...according to my gear, when I'm done, I have ~16 dB of headroom and that's power to spare, brother!

Riis
 
#58
ajota_di said:
Sorry if I don't make any sense at all....
Click to expand...

It's not that it doesn't make sense, it's just that, as has been said before, your amp's pot tapers will not necessarily be anything like anyone else's. Some, for example, are 75% open wrt total output at noon, others are more linear, still others are even less so. So without details concerning your particular gear, your observations concerning dial positions are of precisely zero value.
 
#59
GrowlerBox said:
It's not that it doesn't make sense, it's just that, as has been said before, your amp's pot tapers will not necessarily be anything like anyone else's. Some, for example, are 75% open wrt total output at noon, others are more linear, still others are even less so. So without details concerning your particular gear, your observations concerning dial positions are of precisely zero value.
Click to expand...

My beef, I assumed all pots were linear, even if the loudness/output level change between 8:00 and 9:00 is seemingly different than that of 1:00 and 2:00. Even still, with all gear I've owned, keeping the pots at 1:00 has been the safest bet.
 
#60
Zooberwerx said:
IMO, this discussion is better illustrated by the relationship between a mixer and power amps whereas we identify the clip points of both and establish a quasi-linear relationship. This practice provides improved signal / noise ratio, greater headroom, and no clipping.

Take a look at this dbx manual starting at page 37 / System Set-up and Gain Structure.

ftp://ftp.dbxpro.com/pub/PDFs/Manuals/English/DriveRack_PA_Plus_Manual_18-0483V-B.pdf

Granted, the references are specific for a dbx component but the principles can be applied to just about any sound reinforcement system. Anecdotally, the first time I set up my system, one of the initial instructions was "roll your attenuators back to 37% (11:00)". Say what?!?

Riis
Click to expand...

thanks, that helps a lot. btw it's page 33 :)
 

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