As requested by Arny here's a repeat of the piece that made him "laugh
himself silly". Always willing to help- that's me.
The left-right method for comparing components is not a "test".
I lay no claims to scientific validity. This would require well
designed research to show that it works and who it works for. It works
for me and it might work for others.
I do not claim an invention. It seems to me so common-sensical that I'm
certain that many others thought of it and used it before I ever did.
The task is "Which one of these two components I like better". Period.

) Get a monophonic or near monophonic (eg. centred soprano) signal
source. MUSICAL, not an artefact.
2) On the left insert one component, on the right the OTHER ONE,
Adjust volumes to get the image dead centre.
3) Listen from side to side-write down your preference, get BLINDED..

4) An assistant AT RANDOM either crosschanges both components from
one side to the other or leaves them where they are keeping his
records.
5) If in doubt repeat at least 15 times- for any length of time and
with interval for lunch if you like.
You note your preferred side with each repeat.

.. The changes are the the very crux. of the method,
If rock- certain after 5 to 6 consecutive identical choices end it.
You're not in a lab.

________________________________

FAQs
1) If your preamp has no mono switch you can simulate it using Y
connectors (Radio Shack or similar)
2) I find concentrating on preference
easier than worrying about difference . If you don't want to find out
if you prefer one component over another why would you bother?.
3) If you don't have a clear choice (over 70% for one or the other)
then buy the cheaper or the prettier one or whatever.
4) You can not compare signal source against signal source this
way ie. a cdplayer against a cdplayer, turntable against a turntable.
You cannot compare speakers because that requires special
facilities for moving them fast to an exact position .( Same of course
applies to ABX testing)
You can compare cables, preamps, amps, dacs, equalisers etc
4a) Interconnects are better contrasted if both; preamp to cd player
and similar and cdplayer to amp are changed each time.
5) Room differences, slight volume differences do not matter. If you
still prefer one of the two components even though it is on the "wrong"
side that reinforces the strength of your preference.
Eg. The bass booms on one side of your room but you still
choose the same preamp: "I prefer the sound
of this preamp on EITHER side."

6) The image does not move as you change the components. If it was dead
centre it stays dead centre.
The total of the two volumes stays as it was before the change.
7) I find it easier to be able to compare the two instataneously and
repeatedly by turning my head rather than having them succeed each
other and trying to compare from memory as in A-B and A-B-X testing..
8) The method is single blind. It could be adapted to double blind if
it were to be researched.
In my case it is practically double blind because my assistant (my
wife) does not know a component from a cat and couldn't care less- so
no subconscious signals.
(she might like it better though if it seems cheaper).
9) I offer no theory and am not interested in theoretical
considerations and objections. It works for me, period.
But I'd love to hear if it works for others.
Ludovic Mirabel

Can't resist this one: I can just hear the sound and fury it will
provoke. I proved to myself that silver interconnects sound better to
L. Mirabel than copper and that teflon dielectric sounds better than
polyvinyl.