When anybody wants to debate me on running their amps with the knobs
all the way up in a live PA setting, I'll just use the analogy to the
shutter on a manual or automatic SLR 35mm camera:

The shutter adjusts, automatically or manually, according to how much
light it receives. The MORE light the camera detects, the NARROWER
the shutter aperature or shorter exposure time. The LESS light, the
opposite happens.

For PA Amps, the HIGHER voltage the amp receive from the mixer/audio
chain, the LOWER it's input knobs should be set to achieve the
required volume. The LOWER the voltage received, the HIGHER the knobs
should be set.

I would also tell them that running the knobs all out is akin to using
the widest manual aperature setting on their camera for all
picture-taking conditions: Half of your pictures would all be
over-exposed junk.

-CC

No debate among the knowledgable. To quote a Rane tech note
(http://www.rane.com/note135.html):

"Setting Power Amplifiers

"Much confusion surrounds power amplifier controls.

"First, let's establish that power amplifier
"level/volume/gain" controls are input sensitivity controls.
(no matter how they are calibrated.) They are not power
controls. They have absolutely nothing to do with output
power. They are sensitivity controls, i.e., these controls
determine exactly what input level will cause the amplifier
to produce full power. Or, if you prefer, they determine
just how sensitive the amplifier is.

"They do NOT change the available output power. They only
change the required input level to produce full output
power.

Clearly understanding the above, makes setting these
controls elementary."

Don't you love "Ah Hah!!" moments?




TM



ChrisCoaster wrote:

When anybody wants to debate me on running their amps with the knobs
all the way up in a live PA setting ... I would also tell them that running the knobs all out is akin to using the widest manual aperature setting on their camera for all picture-taking conditions: Half of your pictures would all be over-exposed junk.

"Walter Harley" wrote in message
...
In short: adjust things on your mixer so that it's running in its sweet
spot: as hot as it can go while leaving enough headroom and avoiding
distortion. For most mixers, that means somewhere around the 0 VU mark.
(Which might be 0dBu, or +4dBu, or -10dBV, or whatever.) Then, adjust the
knobs on the PA amp to get the volume you want in the house.

This is not necessary. The output faders on the mixer will control the level
from the mixing position. I wouldn't want to run to the amplifier rack every
time I wanted to change house level!
Simply determine what amp gain is required to give full output with your
mixer at maximum output (minus whatever headroom you desire) and leave it
there. Then use the output faders on the mixer for the purpose they were
designed.

If using a large amp in a small venue, it may be better to reduce the amp
sensitivity to give the maximum desired SPL, but you only do that during set
up, not to change house levels.

TonyP.