Low signal-level preamplifiers are now so easy to do, though within limits...
In the case of a few tens of microvolts or many millivolts these days comparatively easy...forget the BC109Cs and the like from the late 60s, there are many op-amps today that can easily out-perform them, and I don't mean in just Audiofool applications. One might think of the LM833 or the NE5532/4, but there's a comparatively new arrival, the NJM2068. It is quieter, to a degree, than the previously mentioned devices, and around half the cost, though generally that's not an issue.
I've built a few dozen of the following mic pre-amps for a large stage audio mixer, hence me being quiet over the past months, and it lives up to expectations. It's available in the UK (RS for example) and presumably others too. It's a dual device in DIP8 as well as SMD.
There is, or more correctly, were, historically quiet devices, e.g. the LM394, SM2210 and many others, but they're made of Unobtianium these days, and this is a realistic alternative to them. The circuit is for balanced microphone inputs, but at these signal levels, including NBTV/SSTV it's in the best interests to keep low-level sources balanced to reject hum and other common-mode interference. As a mic pre-amp it's hard to beat, even with high-level (loud) sources, e.g. drums and 'energetic' vocalists...but in the quietest of passages it's as good as absent, a straight piece of wire with gain...as far as audio or similar frequencies go.
I'm not saying it's perfect, nothing ever will be, but it's another step forward...
It's designed around dynamic microphones with a source resistance of approximately 100-200 Ohms and a load impedance of 1-2k Ohms.
Phantom powered mics need some other considerations...
Steve A.
I'll come back to the CMRR pot (VR101) for those interested later...
It goes without saying, all resistors must be new 1% Metal Film...otherwise you're wasting your time...ignore the reference to C121...
I've included the NE5532 as it's a back-up to the NJM2068 if that's not available where you are, the pin-out is the same so a drop-in replacement is possible in the future....