Power Amp - set to full constantly ?

[stevebunting]

David A, notwithstanding the info on gain structure, surely the acid test is going to be the overall volume (as in cubic units) of the venue where voodoo and ensemble are working, and, where the speakers are positioned?

 

If he has, according to the gen on the amp, 1200W per channel to play with, then to arrange his sound desk so that the faders are parked on the zero level position, on the desk channels, the gain controls to the amp would have to be set accordingly.

 

If he was playing in a venue the size of the Albert Hall (merely to set the scene for a comparison) as opposed to the back room of a pub say, once the gain structure has been set throughout the program chain, then the only way of reducing the actual output sound level in the venue is to adjust the gain controls on his amp?

 

And, on top of that, there may be the added "complication of the big brother sound level mic" sitting across the mains supply...so the input to the amp would have to be turned down regardless.

 

That is my take on the thread thus far, so if that is not quite right please jump in and do the correction thing.

 

The amplifier attenuation controls are not volume controls. Their purpose is for aligning the input gain to the rest of the system. The master fader on your console is to set the master volume. Not only does it have much finer resolution than the amplifier input controls, you can adjust it from mix position with just 1 fader.

 

If you don't care about gain structure or you require repeatability with large numbers of amplifiers, run the controls at full. If you do care or you have an especially noisy system, set the gain structure properly, label the correct levels on the front of the amp and enjoy a lower noise floor.

[paulears]

If you have the need to operate 2 x 4 Ohm speakers regularly, then a simple series splitter box will do the trick and be cheap to make. A small box, two speakons wired in series to a short length of cable that you plug into the amp. Plug your speakers into this box, and you're away.

[ramdram]

Ref #31.

 

SteveB, apologies for not being more clear; my reference to "volume" was strictly that, literally the volume in cubic units ie. cubic metres. I was alluding to the greater the physical volume the more drop off in sound level there would be, from the source, as the distance increased.

 

The amplifier gain is fixed at whatever the design is. I am not sure I would describe the amp gain controls as being used, per se, to align the input gain to the rest of the system though. The gain controls, in reality variable attenuators, are there to limit the input signal so that the amp does not get driven into distortion at high peak levels, for music with a wide dynamic range say.

 

However, were you to use compressor/limiters or companders or eq or gates or whatever then the input level to the amp from the desk is controlled or modified by said equipment and the gain controls on the amp itself could be fully open ie. no attenuation would be necessary because the levels had been set by the input equipment.

 

I suspect we both mean the same thing up to now but are using slightly different terms.

 

I think that where we differ, sort of, is my view that if you have an enormously powerful amp, and no kit in the program chain between the desk and the amp, and the venue is small, then you might have to use the attenuators on the input to the amp as the ultimate sound level control, IF you want to keep the faders on the zero marks on the desk.

 

Further, and slightly tongue in cheek, the concerns about S/N ratios are not really relevant, probably, in a "rock" concert where the audience's ears have undergone a temporary threshold lift a few moments after the opening chord, and they are there to listen to the band and not their equipment.

[paulears]

Moderation: As we're going around in circles and now explaining our thinking, it's actually getting worse in terms of clarity. As the OP now seems to have ample data on which to work on, I'll close the topic now. As usual in these cases, if anyone has anything they really need to have added - contact a mod and we'll review the new material.