Better Amp better soundstage?

[CK.]

Well, there are several things that are believed to contribute to a perception of soundstage when it comes to equipment, but by far most of them pertain to speakers or the room.

Different kinds of distortion could affect soundstage, but since we have no reason to think there is audible distortion coming from these amps, there's no reason to think they would affect soundstage one way or the other.

The much more likely explanation is sighted bias.

Yeah could be that, I guess even time of day or how fatigue could influence our perception. I guess we would need more info on how exactly he did the A/B comparison.

 

[CK.]

If your amps 2 channels are the same, same flat freq response same zero phase shift no compression no clipping than its not affecting your sound stage. Its differences in left right signals that make left right sound stage, mono signals should all be dead center regardless of your room, your brain uses the first arrival to determine location, the reflections dont matter. In other words, unless your Amp is terrible, misused or defective it should not alter the sound stage.
The most important thing for speakers (something Nuemann says) is a good match in freq. response. Imagine if your left speaker is 2 dB louder in a part of the treble. A mono (panned dead center) guitar playing chords will be smeared across the front (different strings and harmonics in different places) , a guitar playing a solo could also move with the notes.

Yeah agreed, although reflections I believe do matter depending on their time of arrival (localisation effect?). But remember that we are not just talking about an amplifier here, we are talking about a pre-amp as well. phantom center is not at the center in an assymetric room. reflections may not influence the location of the source but can influence the loudness of the source signal that can shift the image.