xy wrote:

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.

Mixer/mic/speaker/room combo. The latter two are extremely important.

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 bet a nickel it's because a tiny tweak of the trim control is a huge
increase in gain, and a large turn of the power amp control is a very
small increase in gain.

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.

In a case when the system is linear, that is the case. If something is
starting to clip or get badly nonlinear, this might not be the case.
But I bet a nickel that what you are noticing is the difference in
control sensitivity and that the actual system gain that causes the
system to feedback is the same no matter where that gain is in the chain.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."