Best way to A / B test amps? Use a switch?

Very good points.  Some of which I have considered but not enough.  

I still think the audiophile thinks his aural memory is much keener than it is and not susceptible to audio forum interference/influence.  But, you're right saying that the "over time" part is also very important.  And there are downfalls to switching as well.

The other part of the issue with me personally is I don't have time to deep listen for hours on end and my environment changes quite rapidly.

I have done extensive A/B comparisons between equipment.  Be it pre-amps, amps, DACS, etc.

My experience is to play a favorite song (say CD) at the volume you like.  remove the CD and play a white noise CD and measure the DB level with a meter.  Then swap the piece of equipment with the one you want to test.  Again play the white noise CD and adjust the level to where it matches the level of the previous unit. Record both unit's levels so you know where to set them when listening.

Making sure the levels are matched before comparing is absolutely important.

Now that you have established the two levels, go for it.

Listen to the first unit with music you know.  Then swap the new unit in. making sure to turn the amps off if swapping amps or mute pre-amps if swapping other stuff.

This has worked very well for me in making purchasing decisions.

enjoy

I still think the audiophile thinks his aural memory is much keener than it is and not susceptible to audio forum interference/influence.

Oh no. How? How could that possibly be the case? Only if maybe someone popped out of the womb and straight away started churning out Fremer-level reviews. Which no one ever did.

We all had to learn how to hear. We all struggled to attain whatever level we are at. For sure that was the case with me. Go read through my posts, you'll fine a whole bunch saying this same thing. Several long ones recount how it took me one full year just to learn to distinguish good DAC from bad CD. Then about another year developing that same skill to a level where- cones, footers, cables, elevators, fuses, panels, on and on-  it seems there's no end to the things that matter. 

And I don't need to match levels, or play the same track twice, or switch fast, or any of that. Which is by the way not bragging nor BS nor even all that unusual. The dealer I learned from never once played the same track twice, and Michael Fremer is somewhere on video saying, "I know some like to do that but I don't." 

That's not to say it can't help. When learning any sport- racquetball, golf, autocross- what's the first thing the coach always has you do? Practice. Break it down to some dumb little part and do that one little part over and over and over again until you get good at it. 

Which, let's face it, nobody very much likes. Well, sorry. Too bad. I mean really, its just too darn bad. Truth exists, and whether you like it or not the Truth is you never get good at anything any other way than by doing it. A lot. 

You want to know the truth? The truth is this fact is so well known I think every single one of us knows this very well. We just would rather delude ourselves and make excuses for our shortcomings, because this is a whole lot easier than admitting the shortcomings.

But hey, your life, your choice. You can make excuses. Or you can do the work.

Choose wisely.

A very human shortcoming is admitting our biases, we make excuses and delude ourselves but the fact they influence us is a very well known phenomenon. Cables, fuses, cable elevators, green markers, magic mats in the panel box ?? I would never hear a difference from any of these silly tweaks and knowing I have biases I also know I could never make an informed decision if I was aware these things were being tested or tried out. I could only make an honest decision if I was unaware but that’s just me I know I’m only human.