When designing a closed loop amplifier for audio the poles of the open-loop transfer function are usually only vaguely known.
These poles can be modeled as \$RC\$ low-passes which attenuate the signal from their break frequency and, more importantly, add phase shift to the signal.
To avoid to much phase shift before gain reaches the 0-dB limit usually a pole is deliberately added at a very low frequency so the open loop gain falls below 0 dB before the other poles kick in.
So far so good. But how can the second, third etc pole be estimated to get a clue where the first pole has to be?
What does the notion of "so much dB feedback is ok to be applied without threatening the stability" mean? How is the applicable amount of dB feedback defined?
An example: I want an amplifier to amplify a signal 30 times and have an open loop gain of say 10000. What does it mean when I say "I apply ...dB of feedback"? Usually I would make a voltage divider of 29/1 and therefore get a gain of 30 (factor, not dB). I don't know how to put this any simpler, but doesn't the applicable amount of feedback depend on how my closed loop gain of the amplifier should be? It's often said that the more feedback the better but when I make a unity gain buffer It is useless since I want to amplify my music, right?
Long story short:
What is meant by the applicable amount of feedback?
How do I estimate the other poles?