First measurements (just to give a taste of it)
A set of Mic preamps tested for SINAD @various gains (20mV 1kHz input)
View attachment 77406
(OK, that's a little crowdy.
Consider it as just a preview at that stage.)
For preamps with ADC, we align them with 0dBFS
The Motu actually saturates before 0dBFS
For the 2 full analog preamps (Mackie and Millennia), I've consider 0 dBFS to be +24dBu (max range on the RME ADI-2 Pro fs R)
Note that the Millennia goes beyond that (the Autoranger II is used to level it down for recording), while the Mackie can't reach it (on Insert out, which is the shortest and cleanest path).
Now we start to understand what makes the cost difference.
The Millennia is, by far, the preamp that gives you the widest Gain range with >90dB SINAD.
The cheaper designs are much narrower: Motu, Mackie, DM1000.
Don't worry too much for a 1dB difference in SINAD: The limit at that level is most likely set by the source signal.
I guess a change in input impedance may explain 1-2dB difference.
What I find more interesting is the trend profile.
The Yamaha AD-8HR is meant to be close to stage and remote controlled, so it presents a very wide range. Obviously, they use some range change to align with ADC, which gives this strange look.
The Focusrite also proposes a wide gain range, but you're far from max gain, at 20mV level (54 gain mark, while it goes up to 80 on 4Pre - the AD8HR is 51 out of 62)
A zoom on the usable section :
View attachment 77408
Comments welcome.
And more to come...