Pre-amps are a waste of time the way they are used on amplifiers. To be effective it would really need to be fairly complex. As executed on CB amplifiers they amplify the noise the same as the signal you want which is a problem today.
Get some sort of notch filter and learn how to use it or get DSP or both and learn to use them. What you want to do is pull out the signal you want with out amplifying the background noise and that just can not be done with a simple pre-amp.
I use EQ, Notch/Band Pass filter both manual and automatic, DSP and either headphones or home or car audio speaker's. Seldom is it a one and done situation.
If you designed a completely different circuit and looked at it like speech processing on TX but on receive the simplest thing you could do would be to select an IC and opamp that gives you eq, compression, gain control, agc, and notching, symmetry control etc.....There have been a lot of IC's in the 1980's and 1990's that where used for portable audio, home audio, car audio gear that had a lot of those functions but not all of them.
I have not tried to design my old gear I have just used off the shelf gear and repurposed it in some cases.
You really want selectivity or the ability to selectively nock down the noise and amplify the intelligent parts of voice data to hear what is going on. So the opposite of what people think they want on transmit audio. Darth Vader is hard to understand over CB in harsh conditions.
This is why a transistor swap is never enough you have to have some sort of filtering at the very least and more sophisticated and controllable the better!
Trying to put that into an amp will be hit and miss due to stray rf and other unknowns!
