To make feedback a good way is to use the sends. Put on your source, for example just the default Operator, on your track. Send 100 % to Send A. Right click on the Send A wheel on the Return A channel and choose "Enable". If you increase the Send A now you will of course get feedback, but it will come instantaneously and will not output any sound. I don't know if it is because of my computer is working too hard with the loop or if it is a safety precaution from Ableton's side.
We now have a loop. The "speaker" is the Send A. The "microphone" is the Return A. But the microphone recieves the signal instantaneously and outputs it through the speakers instantaneously, which isn't how it works in the real world. In the real world you have delay between the speaker and the microphone and in the whole PA. system. So I added a Simple Delay to the Return A. You could also try the Filter. Then I put on a limiter on all the channels. I set the Simple Delay to about 5 milliseconds. Then I added a EQ Eight before the limiter on the Return A to make the right feedback frequency.
I also added an Overdrive to the master channel. Just turn up the Send A on the Return A channel and play a note. Be really careful about the Send A, don't turn it too much up at a time.
This worked in my scenario, but if you need the feedback to come slowly like it does if the gain is just a little bit to high you could try adding Effects to turn down the volume a bit and maybe add a little bit of reverb and try to make it as real as possible. But in my scenario they turn the volume up with an accident which leads to an instant feedback.