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In article ,
(xy) wrote:

hi guys,

i was checking out the gain-before-feedback levels of a mixer/mic
combo. i got it to where it was about to howl, and then backed the mic
input level down just a bit so it was in the "safe" zone.

then i brought up the power amp level. i thought it would tip it back
over the edge and start to get the "about to howl" situation. but it
didn't.

how come i could bring the power amp levels up more without feedback,
but if i barely increased the gain on the mic channel, it would
proceed toward feedback?

i thought once you were at the edge of feedback, any increase in gain
anywhere in the signal chain would tip it over the edge. but i seem
to have gotten away with some extra "gain without penalty" from the
power amp.

why?

power amps are fixed gain devices the volume control effects the amount
of voltage required to achieve rated output at the fixed gain(often
about 29 to 32 dB) but the gain of the amp does not change as you turn
the volume control
preamp often have 60 to70 dB of gain
a small turn on a pre amp is much more gain than a huge turn at the
power amp
of course I might be really confused but I think this is a explaination
for what you experianced

my next related question is this: if you are trying to get a PA
situation set up, should you turn the power amps way up and then keep
the gain controls on the mixer comparatively low to get a better
gain-before-feedback ratio?

run all you gear at the levels proper as indicated on the meters then
turn your amps up to the required level
the amp always can put out the same wattage what the volume control does
is effect the voltage going INTO the amp
George