I believe double-blind tests for music reproduction equipment evaluation is the only method which might produce reliable, believable, and convincing evidence for differences in sound.
However, I know that I have perceived differences in, for instance, amplifiers in my own system. I have perceived differences also in cables, tubes, and some tweaks. I do not and cannot know for certain whether my perceptions are reflective of real differences in the equipment or instead are internal constructs of my biases, expectations, hopes, beliefs, and maybe even aural inadequacies all combined with the fact that I always know when I have changed something in the system. Looking at a gorgeous Plinius amp, all bright silvery power and style, knowing it is playing, and then looking at the non-descript kind of cheap-looking Van Alstine amp I have compared it with, I know my internal, maybe non-conscious, preference is that I really want the Plinius to sound better.
I would love to participate in a double blind test because I wish to know if I am wasting $9000 on my amp when I could get the same thing for $2000 with the VA.
I intend, in fact, to set up the best thing I can in my listening room, which would be a single blind test (the one doing the switching will know which amp is playing but I will not). I will be comparing my pair of Plinius SA100MkIII's to a Sunfire Signature 600. If I can't decide which amp is which after some serious listening and switching, I will be satisfied that I-- and thousands of other perfectly decent, honest people-- have been expensively self-deluded.
Now, I will give my impressions of the Van Alstine 550, current version, as compared to Plinius, Sunfire, Wyred-4-Sound.
I was powering a pair of Shahinian Hawks, a difficult load, when I did the comparison. My PERCEPTIONS were as follows:
In all cases (VA vs. Plinius, VA vs. Wyred, VA vs. Sunfire) the Van Alstine sounded dry, a bit anemic and thin, reproducing strings, for instance, without much sparkle or sheen. There was a lack of bass dynamics and punch. Voices were clear and clean but lacked personality and some presence. There was overall more grain (less immediacy) than on any of the other amps. Somehow, the amp seemed much less powerful than any of the others. Therefore, I "believe" the Van Alstine 550 is a mediocre piece of equipment. But--what would blind testing show???
I don't know and neither do you.
What I do know is that it is certainly possible that it would reveal not differences in amps but flaws in my perceptive acuity.