Question about polarity-inverting preamps

I read somewhere that some preamps invert because it eliminates the implementation of another stage for the signal to pass thru. Maybe someone knows why this inversion occurs in the first place? The designers avoid the issue by having the accompanying model power amp invert too. Some preamps do offer polarity switches.

Many of these amps are single-ended, that is, they have one output signal referenced to ground. In such case, one cannot simply switch signal and ground to reverse polarity. The only way would be to add another stage which ain't the best way. Swapping the speaker leads does it better.

The above have it correct. Conrad Johnson and Blue Circle preamps are out of phase for this reason (less is more) and are among the best.

My moving coil phono stage is out of phase. Since moving coil cartridges have such a low output, adding the additional gain stage to correct the phase would add unnecessary noise to the phono circuit. To correct this I reverse the leads on the tonearm going into the cartridge.

Some preamps (Atma-sphere & Sonic Frontiers to name a few) have phase inverter switches to let you A/B the sound. This is a really nice feature. Happy Tunes!

Is that really "phase inversion" with the Atma & SF preamps, or are those switches really reversing the phase as in polarity?? If so, not exactly the same thing. We had a discussion on this a week ago. Search the other threads.

Those that own those preamps can test it. Play some music with a loud whack of a bass drum or something that makes the woofer on your speakers push out a lot. Then try it again after pressing the switch on your preamp. If it is inverting the phase 180 degrees, the woofer will now be sucked in a lot, instead of pushed out.