PA level control question.

[catphish]

I read in the Yorkville pro audio basics guide that typically you will usually run your power amp with it's level all the way up. Is that right? Why?

[Rickr]

I'm no expert, but I'll explain it the way it was explained to me. Think of it as a water line with 2 valves, the amp valve 1 and the speakers valve 2. If you have the amp valve turned down, and crank the speaker valve wide open, you may not have enough water (power) to supply the speakers. With the amp wide open, you get a quicker, better response. But (isn't there always a but) you wouldn't want to trade off sound quality. If your amp is quiet at 75%, but load at 100%, run it at 75% and turn your mixer up.

 

Did that help,

 

Rickr

[B. Adams]

The level controls on power amps are input attenuators, not output. Having the amp turned all the way up allows the entire signal into the amp. Having it turned down a little won't necessarily lower the output level, only the input level. If you input a strong enough signal, you can still get the full output.

[IsildursBane]

I'd say it should be set to give you the most control on your mixing board. Have it set so that topping out your board is too loud, but seomwhere in the middle is just right. If you turn your amp up too loud, you have your board settings low and still be killing people.

 

-Dan.

[Craig Vecchione]

The only situation where I'd lower attenuators is for something like playing a room way too small for the rig, where you simply can't set up good gain structure before the amp without blasting holes in the building.

 

Further to B Adam's comments; never confuse amp input attenuators for protection. The amplifier is alway running at full potential, and a high enough input signal, even if attenuated, can result in damaged equipment. It's always a good idea to have effective limiters in the system.

[catphish]

 

Originally posted by Craigv The only situation where I'd lower attenuators is for something like playing a room way too small for the rig, where you simply can't set up good gain structure before the amp without blasting holes in the building. Further to B Adam's comments; never confuse amp input attenuators for protection. The amplifier is alway running at full potential, and a high enough input signal, even if attenuated, can result in damaged equipment. It's always a good idea to have effective limiters in the system.

 

 

Well, it's approximately a 30 x 60 foot bar, and my amp will be putting 600 watts into the mains. Should I crank it and rely completely on my mixer?

 

Please answer keeping in mind I'm a novice, and would prefer to err on the side of being safe.

[Craig Vecchione]

 

Originally posted by catphish Well, it's approximately a 30 x 60 foot bar, and my amp will be putting 600 watts into the mains. Should I crank it and rely completely on my mixer? Please answer keeping in mind I'm a novice, and would prefer to err on the side of being safe.

 

 

It's really hard to guess without actually being in the room. An empty 180sq ft room is a lot more reflective than one filled with drunk patrons, so it will change as the night wears on.

 

There's no 'safe' implied by lowering the attenuators....a dropped mic is still in danger of sending a huge signal spike that will damage a driver. The amp attenuators are really only intended to 'cool off' a too hot average signal from your board or final processirs. They're not intended as volume controls per se.

 

I'd leave them at full and set up the system, and only lower them if you find it impossible to have masters at 0dB and the highest-volume channel faders nearly at 0dB without having to cut the channel gains really low, or of course if the amp's clip lights are coming on at all.

[catphish]

Originally posted by Craigv It's really hard to guess without actually being in the room. An empty 180sq ft room is a lot more reflective than one filled with drunk patrons, so it will change as the night wears on. There's no 'safe' implied by lowering the attenuators....a dropped mic is still in danger of sending a huge signal spike that will damage a driver. The amp attenuators are really only intended to 'cool off' a too hot average signal from your board or final processirs. They're not intended as volume controls per se. I'd leave them at full and set up the system, and only lower them if you find it impossible to have masters at 0dB and the highest-volume channel faders nearly at 0dB without having to cut the channel gains really low, or of course if the amp's clip lights are coming on at all.

Sounds good. Thanks again.

[RainsongDR1000]

I have somewhat the same question (I think). I'm running a carvin PA620, 200 watt Power mixer. There is a volume knob for each indiviual channel and a main volume knob. From what I can decipher from the instructions, they recommend not running the individual knob settings higher than the main knob setting. Is this correct? For the venues I play I am running the individual channels at around 3-4 and the main volume control about 3-4.

Does this sound right or should I run the main one higher to get more power to the speakers and adjust the individual knobs lower or would it be the other way around? I have 3 way acoustic suspension speakers rated at 300 watts and want to drive them as efficiently as possible to get the most bass response out of them. Any suggestions?

[mrbobo]

It's called "gain structure". You want your mixer and amp to clip at the same time. If you max your amp attenuator, it will clip far before your mixer will. You will not get the most signal to noise ratio.

 

Put simply:

 

1) unplug your amps speakers. set amp attenuaters to infinity or zero.(most amps have protection, that prevents harm when no speakers are attached)

 

2) put in a test cd - music or pink noise.

 

3) bring up mixer masters until it clips, then back off just a little.

 

4) bring up amp attenuators until the amp clips - then back off just a little.

 

This will yeild the lowest noise, and you still achieve 100% of your amps rated output.

 

I did a quick search on the net and found this website, explains it in more detail: http://www.thenoizeworks.co.uk/tech2.html

[kerOseen]

 

Originally posted by Craigv The amp attenuators are really only intended to 'cool off' a too hot average signal from your board or final processirs.

 

 

Wow, I've read some great tips from this thread. One more question to add:

 

Is putting a compressor in line before the amp a passable way to control speaker damage, say from spikes and/or overdriven channels? Of course, this would be only in the case where an outboard limiter isn't available.

[kerOseen]

Originally posted by kerOseen Is putting a compressor in line before the amp a passable way to control speaker damage, say from spikes and/or overdriven channels? Of course, this would be only in the case where an outboard limiter isn't available.

 

[mrbobo]

Yes, but the proper gain structure I mentioned above still applies.

[kerOseen]

 

Originally posted by mrbobo Yes, but the proper gain structure I mentioned above still applies.

 

 

Cool, thanks for reiterating that, I can see your point that proper gain structure is neccesary throughout the entire signal chain.

[lucho_84]

 

Originally posted by mrbobo It's called "gain structure". You want your mixer and amp to clip at the same time. If you max your amp attenuator, it will clip far before your mixer will. You will not get the most signal to noise ratio. Put simply: 1) unplug your amps speakers. set amp attenuaters to infinity or zero.(most amps have protection, that prevents harm when no speakers are attached) 2) put in a test cd - music or pink noise. 3) bring up mixer masters until it clips, then back off just a little. 4) bring up amp attenuators until the amp clips - then back off just a little. This will yeild the lowest noise, and you still achieve 100% of your amps rated output. I did a quick search on the net and found this website, explains it in more detail: http://www.thenoizeworks.co.uk/tech2.html

 

 

 

now when you say this do you mean all the way up(as far up as it goes)? or set to 0 on the numbers labeling the knobs?

[kerOseen]

I think he means start at zero (all the way down) and bring it up till the amp (or mixer) lights "clip", then bring it just below clipping.

[B. Adams]

Infinity is all the way down, and the symbol looks like an 8 on its side. I'm sure you've seen that before though. So yes, in this case he meant zero as infinity, not zero as unity. I've caught myself calling them both zero before too.

[lucho_84]

thanx. i actually use that in stats all the time. but i don't have a power amp here to lok at so i didn't really understabd. and mental pix didn't help either;) lol

[Craig Vecchione]

 

Originally posted by mrbobo It's called "gain structure". You want your mixer and amp to clip at the same time. If you max your amp attenuator, it will clip far before your mixer will. You will not get the most signal to noise ratio. Put simply: 1) unplug your amps speakers. set amp attenuaters to infinity or zero.(most amps have protection, that prevents harm when no speakers are attached) 2) put in a test cd - music or pink noise. 3) bring up mixer masters until it clips, then back off just a little. 4) bring up amp attenuators until the amp clips - then back off just a little. This will yeild the lowest noise, and you still achieve 100% of your amps rated output. I did a quick search on the net and found this website, explains it in more detail: http://www.thenoizeworks.co.uk/tech2.html

 

 

Backing off just below the point where clip lights illuminate is no guarantee of no clipping, and is probably still at a level of overdriving the device be it mixer or amp. If you have no other means of gauging level, I'd go a bit lower.....sacrifice some signal to noise ratio, which isn't noticeable while playing, in order to reduce distortion, which is definitely audible if present. If your mixer has meters and a PFL setup, you can easily set at least this part of the gain structure properly.