A phono preamp with equalization selector

Of course that is possible, but do you think it really has to do with the "1980s"?  More likely that a single particular recording regardless of the time line, might by chance sound "better" using an equalization curve other than RIAA. (And Columbia is not far from RIAA, anyway.)  And besides, what does "better" mean? (It's a subjective judgement.) The point is that nearly all companies (I say "nearly all", because I don't doubt that someone can find an exception or two) used RIAA certainly by late 50s/early 60s.  I think Fremer is claiming RIAA took over even earlier in the history of the LP. In the early or mid-50s, my parents had a Harmon Kardon mono, tube receiver that offered RIAA, Columbia, and one or two other choices for equalization, but note the date.

My Audio Research Reference 6SE has Columbia and Decca. Used in the 40’s and 50’s as well as RIAA.

"A friend noticed me they should be played with Teldec equalization plus inverted polarity,"

Some friend you have there-encouraging unecessary audio nervosa.

ghdprentice

My Audio Research Reference 6SE has Columbia and Decca ...

That's your 3SE, George.

GHD, You say "used in the 40s and 50s".  For most of the 1940s, the 33 rpm LP as we know it today did not yet exist.  I think the very first such records were produced in 1948-49.  It was the introduction of this then new technology that necessitated the new equalization curves. 78s and whatever else was in common use through most of the 1940s were certainly not equalized according to any of these algorithms.  From there, I refer you to the article by MF that I referenced above. Whatever one might think of MF in terms of his opinions as an equipment reviewer, I do trust him to do a thorough job of research when he addresses these general subjects that apply to the hobby.  I take Ralph Karsten's (Atmasphere) word as well, that the companies that made the equipment upon which LPs were cut (Westrex, etc) who determined what equalization curve to use, and that all of these companies had adopted RIAA by the mid-50s. (Yes, I suppose there are rare exceptions, but I don't know of any, and maybe they did it differently at first, in the UK.)