How are you playing your precious MONO Vinyl?

"Mono LPs pressed from 1948 until the early-mid 60’s have a groove width of 1mil.  Mono LPs pressed after the mid 60’s and including current mono reissue LPs have a groove width of .07mil...a smaller groove width. "

Not that it matters much, because the point is correct but the numbers are not.  Stereo grooves are 0.7mil in width, not .07mil.  Also, I have read that the 1mil groove went out in the late 50s or even earlier, not the mid 60s, but that factoid was not documented any more than is the claim it went out in the mid 60s. There was a period of time in there when top artists recorded the same material both in mono and in stereo, two entirely separate recording sessions. For example, I have a recording by June Christy, "Something Cool", separate versions in mono and stereo.  Same album cover, same sequence of songs on each, but if you listen to both, you can easily hear differences in phrasing of lyrics and in the improvisations. Both on Capitol. One wonders whether there is any difference in groove width between the two versions and whether an LP side with 1.0mil grooves for mono would have to contain fewer minutes of music than a corresponding recording in stereo which has to use 0.7mil grooves (because 1.0mil grooves would take up more space).  I am sure there is someone out there who knows.

“I’d say that in this case, everything hinges on the design and sound quality”

@goofyfoot 

Exactly, the value of a two channel mono phono preamp comes down to design execution, sonic character, how it complements my system’s voicing and not some theoretical advantage from its dual-mono nature alone. 

My current phono has ONE input. If I don’t hear any audible advantage with EQ-100, I may upgrade to a high quality stereo phono preamp with TWO inputs and that would be the end of my phono quest for a foreseeable future. 

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.