Here you go … the Midas XL3 Pre amp design … not hard to find !
Thanks for these. Always interesting to look a the various ways to skin a cat. (The Midas mic pre is on or around page 65 of the manual.)
I'll stick my neck out and say that to the extent that there are any audible differences between MODERN, decent mic pres (other than noise floor) it is due to differences in the network that goes between the mic and the first gain stage. This network needs to do several things that lead to some design tradeoffs. In no particular order:
*Preserve common mode rejection.
*Supply phantom power, when needed.
*Provide electrostatic discharge (ESD) protection.
*Provide radio frequency rejection.
*Preserve noise performance.
*Determine the electrical load on the mic.
I probably missed some. JR?
Generally, providing better protection against the insults of high voltage and RF forces you to take a screwing in noise, and maybe high frequency response, if you get extreme. Also, depending on the design, more expensive components, such as better matched resistors and larger coupling caps could make a small difference in noise performance. And some mics might be affected by the load on them.
But after that it's all just gain, so as long as you don't overdrive it I doubt anyone can hear the difference between any reasonable audio op amps.
Now ADCs, and perhaps their drive circuits and anti-aliasing filters, might still get better. After all, no ADC has low enough noise to use all 24 bits and maybe, MAYBE there are some other artifacts of the conversion process that could be audible in some circumstances.
I while back I was playing with a signal generator and a cheap ADC running at 48 kHz and found that if I blasted enough 25 kHz into it I could indeed hear a 1 kHz tone (the expected aliasng product). Would this ever make a difference on speech or music coming out of a mic -- I doubt it. (Maybe if you jangle your keys really hard in front of an Earthworks.)