But it has everything to do with listening protocol, bias and perception. And one attempt and a difference can be from a lucky guess, nothing more. Now, if you performed a credible DBT with levels matched to .1dB spl, and was able to differentiate between the two 15 out of 20 attempts, (not so easy) then you have something legitimate and perhaps do this outcome consistently.
Writing things down is subjective in itself as well. Prone to cause problems, especially for just one such writing.
Now either there was something wrong with my 2500 or the 2600 has a better amp section.
Yes, one of the units could be defective. That is always a possibility. Therefore, it would have been good to test the unit if it meets factory specs.
The 2600 uses different parts in the amp section than the 2500, I can not tell you if that is the reason for the improvement but it is a slightly different amp.
That is not the issue either, nor a possible different topology. These are audio myths and urban legends.
I just read a review in the on line, paid subscription, Audio Critic, of a $5K Bryston 8ch amp and a $230 BehringerA500. Sonically transparent, both of them when not clipped.
Also, remember I was not the only person who noticed it either.
Yes, I know of these inputs: a wife heard the difference, from another room at that, and she is not even aware of what is going on in audio.
You see, these other persons are equally biased. No one is immune. You have to test properly, or it is unreliable and not much meaning to it.
To be honest, I don't see why some are having such a hard time believing it anyway.
It has nothing to do with believing. That is based in faith. What one needs to convince is with credible data from credible listening protocols. I am afraid yours and countless others are just anecdotes of unknown quantity. Besides, 30 years of DBT listening has shown that when differences are present, it can be measured in a big way. And, well designed components are transparent.
I am the biggest sceptic when it comes to stuff like this and I was excpecting the 2600 to sound exactly the same as the 2500. I only traded up for features. I was pleasantly surprised.
Trading up for features is as it should be about
Being a skeptic doesn't give one immunity from bias or an ability to conduct a good comparison.