How are you playing your precious MONO Vinyl?

@lalitk So then the question is whether or not you gain anything by using this two channel mono phono preamp. I’d say that in this case, everything hinges on the design and sound quality. But from what I’ve read here, more than likely no, there’s no difference between using a mono or stereo phono stage if the cartridge is a mono cartridge. So you have three tonearms but do you have three inputs on your phono amp? The ASR Basis I mentioned has two inputs. If you’re having to switch out your phono cable and you don’t care about the inconvenience, then one phono amp is likely all you’ll need. But as I mentioned before, I’d focus more on getting a great sounding phono preamp and not at all about whether the phono stage is mono or stereo. Unless this EQ 100 just flat out sounds amazing.

I really don’t know why I would ever need a separate mono phono-stage when I already have a great stereo phono-stage. Even if I really want to run a one channel system I can just connect one channel of my phono-stage (which happens to be a dual mono layout internally, at least in part, AFAIK). I guess if one wants to have a separate complete mono system for mono records then a mono one-channel phono-stage makes sense. Even then my phono-stage has two sets of outputs so I could even send a stereo output to a stereo system and a mono output to a mono system.

"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.