I'm not sure I understand what you are asking. There must be something I did not explain clearly. Taking your last part.
Biasing current is generally taken to be the output stage current that passes when there is no signal. This current rises and falls as the signal passes. For this Single Ended ClassA amplifier it cannot fall below zero mA (i.e. 5mA - 4.99mApk)
If your signal is symmetrical, then it will rise to 5mA+4.99mApk so your 5mA quiescent current varies from 0mA to 10mA when the maximum symmetrical signal is passing. But that's not the way a single ended amplifier works.
At very low signals the + or - output current simply adds or subtracts to/from the bias current. Distortion is low and the amplifier is referred to as being linear. A SE amp does not stay linear as output current increases towards bias current. Distortion rises as signal current rises. By the time the signal current is near half the bias current the distortion has become noticeable and gets worse for more signal.
I have no idea why you chose common base (CB) as an extra stage. Great as a cascode. Exceptional HF performance. Useless In/Out impedances when used for the wrong duty.
The input bias resistors do lower the input impedance. They effectively set your limit.
A good guide for selecting these:
assume the base current drawn from the series pair is <10% of the resistor current. We ended up with 240k+100k across 12V, so current = 0.0353mA. That would indicate that the base current should be less than 3.53µA. We have a collector current of 5mA. The required hFE becomes 1400. (oops, the resistor values are too high) I did not check that and should have used 33k and 33k*2.47 = 82k as input resistors. There is another trick that can be used, but I'll not complicate this long reply further.
Clipping is not strictly what happens in a no global feedback Single Ended amplifier like this. The distortion simply gets worse as the signal increases. It becomes so bad that even an oscilloscope shows the gross distortion long before you reach that 0mA to 10mA current range I talked about earlier. Most of this distortion is 2nd harmonic. Some here promote listening to amplifiers that produce 2nd harmonic with a little 3rd. Most amp designers do not agree.
Black invented feedback to allow the telephone calls to be intelligible after passing along the long lines to get audio into the handset.
Global NFB brings in a very different behaviour. I'll leave that for another Member to explain. It's getting beyond my capabilities. But one thing NFB does bring is the sudden onset of clipping and the millionfold increase in distortion for a 10% rise in signal level when the current/voltage limits are approached.
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