How are you playing your precious MONO Vinyl?

A "two channel mono phono preamp" is any phono preamp or phono driving a linestage where the mono mode is engaged, when you feed that phono section with a true mono cartridge. Lalitk, I don’t understand exactly what you are after. If you want to go the ultimate purist route, then use a true mono cartridge with only two pins for output driving one channel of a stereo phono stage which in turn drives one of the two amplifiers driving one of your two stereo speakers, like Elliot says he sometimes does. The added advantage of the EQ100 is only the ability to select the compensation curve. If you don’t know for sure what pre-emphasis curve was originally used, then fiddling with the de-emphasis curves is pure guesswork. You might find one curve that pleases you most, but you cannot be sure it is the algorithm that was actually used in the making of the mono LP. I’ve got one set of mono LPs, Louis Armstrong and Ella Fitzgerald, the classic recordings, on EMI in mono (UK pressings), where when you play them with RIAA filtering something sounds off.  Whereas the original US pressings on Capitol (I think, or maybe Verve) sound wonderful with RIAA filtering.  I have always suspected that the EMI pressings were done differently in some way.  Of course, no matter what, the music is sublime.

@lewm Sorry to verge off topic a bit but weren’t the grooves in the mono micro groove pressings wider than the stereo grooves but more narrow than the original mono grooves?

Not a groove expert. I only have read what I wrote, which only applies to the 33 rpm era post ~1948. 

“I don’t understand exactly what you are after”

@lewm 

Let me try to clarify. 

You described how your UK EMI mono pressings of Ella & Louis sound “off” with RIAA EQ, while the US originals sound wonderful. I was just curious: have you ever tried listening to those UK EMI pressings using a different EQ curve, like CCIR or EMI, if you have access to a phono stage with that option (like the EQ-100)?

Sometimes switching to a different EQ curve—by ear—can make those “off” pressings come alive. I’m not suggesting it’s about being historically precise, but rather asking…. have you experimented to see if any other curve actually sounds better to you on that specific recording? 

I recognize without definitive info on the original mastering EQ, dialing in playback EQ is largely educated guesswork. And while something like the EQ-100 offers flexibility with its 10 curves, it’s ultimately your ears not the curve selector that decide what sounds “right.” 

That’s all I was getting at—purely from a listening and enjoyment perspective.

As I said before, EQ-100 is an interesting product and it may lead to new discoveries, such as musical expressions and the performer's intentions that have previously been buried or hidden. 

I don't have any phono stages with options for the de-emphasis curve.  They are all RIAA.  And since this one pair of LPs on EMI are the only LPs where I have ever noticed a possible problem, it has not and will not be worth my while to buy one.  I have several other copies of Louis and Ella both original pressings and re-issues that sound fine with RIAA.  I would wager those EMI pressings are original in the UK, because the LPs are obviously very old; the quality even of the album cover jackets is sky high. If I ever have access to a phono with options for EQ, I will give them a try.  when I was a kid, my parents had a Harmon Kardon mono receiver which did provide at least 3 curves.  I used to play with them while listening.