Phase inverting preamps

I see a LOT of completely wrong information here. 

@elizabeth 
No. Gain stages have nothing to do with inverting the signal. Gain stages invert the signal only when the gain device is operated in common source or equivalent mode for the particular gain device. That's the mode that gets you only voltage gain which is all you need in a pre-amp since the load a pre-amp drives is of high impedance and requires very little current. Common drain and common gate modes get you only current gain or both current and voltage gain, respectively, and both of those modes are non-inverting. It has nothing to do with swapping left and right channels. You can't just rewire your RCA cables backwards either. Swapping the polarity of the speaker cables is the easy fix. If we're talking about an inverting phono pre-amp, you should reverse the wires to the cartridge. 

Just had a bit more time to read over this....

@herman 
For the intent of this discussion, you're really splitting hairs with the terms "phase" and "polarity". I signal that's experiencing 180 degrees of phase shift is the EXACT same thing as inverting it's polarity. Maybe there is some phase shifting going on inside a component somewhere, a few degrees + or - here or there, but that's the nature of the beast. But that's not what we're talking about here. 

Whether or not hairs are being split is a matter of opinion. That you are incorrect is a fact.  As I stated earlier, a phase shift is a difference  in time whereas inverted polarity means a change from positive to negative or vice versa. 

I don't have any illusion that any of this discussion will change the terminology, but I do think we should understand that phase and polarity are not the EXACT same thing just because audiophiles use the terms interchangeably. 

If you take a pure sine wave and shift it 180 degrees then it will look EXACTLY the same on an oscilloscope and will sound EXACTLY  the same. However, if you take a "signal" containing many different frequencies like music you get a much different result. Since each frequency has a different period,  if you shift each frequency by the same number of degrees  it will sound different because each frequency is shifted by a different amount of time which results in a waveform that is not the EXACT same thing.  That is a reason why speaker crossovers distort the signal. Here is a discussion of it.

https://www.passlabs.com/press/phase-coherent-crossover-networks

Phase or Polarity?
http://totalproaudio.stevebunting.com/30/basics/phase-or-polarity/

herman

If you take a pure sine wave and shift it 180 degrees then it will look EXACTLY the same on an oscilloscope ...

Pretty much!

... and will sound EXACTLY the same

That is very debatable. My preamp has a phase invert switch and on some recordings, the difference is very audible.