He used to hear differences between them all the time till the early 1990-s, and then, when he started level matching them to within 0.1 db before conducting a blind test (single or double) he suddenly found they all sounded the same because (as we discussed earlier) they have negligible differences between them in measurements. In fact measurement devices are much more sensitive than the human ear, and will show differences that we cannot hear. So Aczel says ( and many do agree) that the differences we tend to hear when we swap components are largely because of volume changes (if they are not level matched precisely) interacting with the room etc.

You are correct: he never reviews tube amps because they WILL sound different (in other words will color or distort the signal). That some of us find that pleasant is outside the scope of his writing, he is only interested in high fidelity equipment.

So why does he even bother to review amplifiers, CD players & preamps? Becuase, as he says, people buy equipment for how reliably it's made, how nice it looks, and maybe even for infitesimal improvements in measurement that cannot possibly be heard but may just make them feel good, knowing they have the best.

For example, in his reviews, amps by Bryston are excellent. they perform superior to most amps, (even though this superior performance is not really audible since even cheap amps have only slightly less performance) and can be overdriven quite a bit. he also likes Carver amps. Amongst CD players, he likes Sony players in general. Again, even cheap CD players wil sound the same according to him.

BTW, Aczel is not the only one who ay this. A lot of industry professionals say this. For example, Dr. Earl Geddes today always displays his $5000 (retail) Summa cum laude speakers with $200 worth of electronics (amp & source). See Rocky Mountain Audio fest reports to verify this.

It's fun to see the "tweako" reviewers
talk about how transparent his speakers sound, and how they can "hear" the inferior electronics he uses, and if only the "old fool" would conform to industry dogma and use expensive sources & amps (which I am sure they will gladly provide ) how much better his system will sound.

Like I said, if this concept really gets out, a lot of the high end industry would just shut down (except for speaker manufactureres of course). Hence the crzed bashing of Aczel...he has been successfully reduced to a by-word in the industry...an skeleton so to speak, and at age 80 I don;t think he even cares.

That said, I use a $2200 (retail) CD player in one of my systems. Why? Cos it's made in W germany (a Berendsen cdp-1) & uses:
D/A converter: Crystal CS 4390 with resolution
equivalent to 20 Bit
Reconstruction filter: purely passive
Output driver configuration: Discrete single-ended class A.
Does it sound better than my $700 (retail) Sony Xa20-ES? I have never done a DBT but I believe Aczel. It probably won't sound better. But I didn't buy it for the "better sound" I just try to buy stuff based on my perception of quality.

Hope this helped out some of your thoughts.
-akhilesh