Gain Setting Question

pangell44

Love the forum. Have learned a lot of useful information.

In reading through the detailed gain setting posts, I had a question. I have heard and read, quite possibly incorrectly, a theory that disconnecting the speakers from a power amp actually changes the ohm load its seeing and has an effect on the point where it will clip. So when you disconnect the speakers to set the input levels on the amp, are you actually not getting the same true point of clipping that you will see once you restore the load?

The answer might be absolutley not, but I was just curious if these theories I've read have any merit.

Thanks

Gadget

Well, I can't say that it has NO effect, but then I am pretty certain it's negligible...When you consider that to be twice as loud as 100 watts you would need at least 1000 watts... there are other factors like the amps damping factor, and Back EMF...and that is why we say till it clips and then back it down a few dB.

Dra

This is an assumption on my part but the clip lights may be indicating a clip of the input. The circuitry may be designed so that when the input is clipping that the output is as well. Kind of a zing-yang. The clip lights don't actually mean clip, but rather close to clip. Consider this. The output of the amp with no speakers attached can't ACTUALLY be clipping because there is no output. The power supply CAN'T be exhausted, because it is drawing no more power from the wall while there is no load.
Am I wrong? It sounds right to me?

DRA

pangell44

Thanks for the replies!

One other quick question around gain structure, and maybe its a dumb question, is that I get the whole concept of what and why you are setting it through the chain. What I never see then discussed in detail, or I'm missing it perhaps, is you run your test signal, set the board to unity, adjust the amp gains, adjust the limiters on the driverack, etc.

Then it comes time to for the band to actually play in a venue. Assuming that unity is not the ideal volume, where you do reduce the volume to keep the best SNL ratio and gain structure? At the gain stage of the board? The channel faders? The main faders? The power amps?

I'm sure there are different theories, just interested in what you've found to work and sound best as a starting point.

Philip

Dra

Not that it addresses the main question, but the gain setting process we describe is simply for the driverack and amps as it relates to the main outputs of the mixer as the meters' reach the level previously found as "max". For live / real music each channel / source has to be set to optimum.

DRA

pangell44

Thanks, Dra.

I guess what I'm asking, and again it might be a dumb question, is where is the best place to cut back the volume to keep the best SNL and gain. Do you run the channel faders near unity and cut back the mains, run the channels and mains near unity and cut the amps? I guess I never thought about how to do it the best way, I just set the volume to the right levels.

Dra

If you post this question on PSW, you will get arguments for both sides. and both will present good arguments and both will be right. In the end, as long as the channel inputs don't clip and the master output stays at you pre-determined max... it doesn't matter.

DRA

Gadget

The correct answer is maybe ... In light of my own recent discoveries regarding digital audio it kind of depends... the caveat here is that with individual channel, if they are run too hot.. you get buss summing overload, and the sound becomes harsh and more digital sounding.

Here though were talking an analog board I assume, and the place where it makes MOST sense is the master volume of the board. The individual channels (multiple) would be a BAD place to start reducing your volume because there are multiples of them and if you start adding a little noise on each channel... well you get the picture..

That and the gain of the driverack is a PITA when your talking real time correction.

pangell44

Thanks again!

Something Gadget said in the Start Here post is so true... "As you go through this stuff you will find that the more you learn the less you know."

Luckily this is a great place to learn!

Gadget