The purpose of a Differential amp is to allow through signals that are different from each other.
The Signal(+) and the Signal(-) line are opposite phase, one goes plus while the other goes minus. Since in is (+) and the other is (-) they are as different as they can be.
However, that is not true of noise. The two wire act as antennas and pick up stray noise in the air, and noise emitted by other electro-magnet sources like power cables and so on. But, and this is the KEY, that noise is the same on both wire. If there is a blip of noise the goes positive on the (+) wire, then that same blip goes positive on the (-) wire.
You see now that noise is the same in both wire, but anything that is the same is lost; I mean really and truly lost, which in turn means any noise the wire pick up is gone.
However, the difference in the signal is exaggerated. Even if there is noise, because the combined (+) and (-) signal is exaggerated, it means the Signal to Noise ratio is lower, even if we, for the moment discount, the cancelling of the noise.
But just because the INPUT signal is exaggerated, doesn't mean it gets amplified more on the output of the pre-amp. I suspect the gain through the differential stage and the following amps is pretty much standardized within the context of standard Line Level inputs.
So, just because you have more on the input, doesn't mean you have more on the output. Even if the input stage had more gain, you still set the output volume using the Volume Control and judge the level by ear. I don't use numbers when I set my volume level, rather I set it to the level I want to hear regardless of any dials or read-outs.
So, the output will not be louder, unless you turn it up louder.
Let's use another example, say I have very efficient speakers, approaching say 100db Sensitivity, you still set the volume level based on what you hear. It takes a stubborn man to always set the volume at 70 or at 11 o'clock or at 0db regardless of what his ears tell him.
It matters not if the XLR are louder, quieter, or the same, you turn the volume dial until you hear what you want to hear. Simple as that.
What does matter is that the noise level on the XLR inputs is very very very very low.
Last edited by bluewizard; 09-01-2014 at 06:24 PM.