=Willen;1118323]I did little experiment with the pre-amp applying different voltages. Is it valid?
I found audio source (mV) is directly related to bias factor. Is it determined by a resistor for electret mic (gain controller)? Or by attenuator (audio to ground) resistor while injecting line out audio? I used 50mV to 9V. Check the amplitude, which is the best peak to peak and which level starts to distort audio?
Pre-emphasis boosts high frequencies. Distortion is high frequencies so distortion is also boosted by pre-emphasis.
A transistor without negative feedback produced by an unbypassed emitter resistor has high distortion when its output voltage swing nears the positive supply. The voltage input change causes an exponential (instead of linear) voltage output change. Then a higher supply voltage allows the transistor to produce less distortion.
I never tried Collin's (Talking Electronics) very high value resistor to power an electret mic and attenuate it. Instead I use the datasheet value of 10k for a 9V supply so the current is the rated 0.5mA, the DC voltage is the correct at 5V and it is sensitive. I think Collin's very high value resistor causes distortion.
You do not want powering a mic to attenuate the signal because then the preamp must have extra voltage gain which also produces extra distortion.
Instead you want the mic preamp to amplify the low level from the mic with low distortion. The distortion Is less when the supply voltage is high.