xy wrote:

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?

Aside from the good answers you've already heard, another possibility
is that you had been overdriving the preamp in the mixer until you
backed off the gain control. When you overdrive a circuit, you produce
a whole lot of harmonic distortion. This results in new signal being
added at various frequencies that weren't there before. If those
frequencies are the wrong ones, they can trigger feedback in the room.
You'll notice this with guitar amps a lot: It's easier to get a
distorted guitar sound to feedback than a clean sound. With a clean
sound, you generally need more volume.

So it's possible that you turned up the channel trim to the point that
it was distorting , and you heard feedback, so you turned it down a
bit. Then when you turned up the power amp, you were increasing the
volume level without overloading any circuits.

I still agree though that the most likely answer is that the gain knob
on the mixer is more sensitive than the attenuator on the power amp.

ulysses