This is a great thread ! There are lots of mono "info and visuals" throughout AK, especially in the TUBE AUDIO and TURNTABLES sections. General Audio seems to have too many trolls and commenters without useful added info. Mono and Stereo Phono Preamps have been my focus for the last decade and here at AK, Turntables is the "forum for all things analog" even though here at Tube Audio there sure are many tube amps and preamps, both mono and stereo. I seem to post here re: Tube amps and at the TT forum to share my Preamp Phono EQ enthusiasm.
AK has many merits and has drawn a huge crowd of sincere listeners willing to share their experiences.
Whenever anyone yearns more info re: anything, here at AK, the SEARCH function is your friend...
Many of you realize the listening experience in mono can sound very involving, just as involving as your fave stereo. For many of us, the nostalgia of a simple system playing old discs really weighs in, as well. Hearing the hits the way we remember them has always been a factor for my equipment choices, as is the term "I wonder what HiFi gear my favorite musicians listened with" seems to influence me...
I "grew up" with stereo, but I remember my 10 year older sister listening to 45s on a semi-portable record player when I was a toddler. Later, we had a TV console with a HiFi inside, in the family den. Then, my 5 year older brother got his first real stereo circa 1968. Around 1970, in our room, we were listening to his all Dynaco ss components, AR XA tt w/Shure M91E thru KLH 5s. Too bad the speakers were high atop the bookshelves and close to the rear wall. Mono discs were not treasured yet, but his record collection sure grew quickly.
Of course, when Sis moved out of her room, I was a Junior in High School and got her room for myself. Woo Hoo ! In '73 to '74, I was a good boy (grounded much of the year to tend to scholastics) and as my grades climbed, I convinced my Dad to let me have my own stereo in my room as a pre-graduation present. It worked well, but not at first. I found a used AR stereo integrated amp and Dad let me buy lg. Advents and a decent Pioneer tt w/Stanton 500. However, my older brother decided that (DO NOT TRY THIS AT HOME

If we hook up the amps in parallel, to his KLH 5s, we can double the power with his 60wpc Dyna amp. Naive, I cautioned him to please not do this. Of course, his "vision" was enforced and he literally blew up both amps, but his speakers stayed alive.
The reason for this long winded story is: That was the moment I knew I had to find out why and how the amps self destructed when wired together. That incident and my love of music, literally influenced me to soon find an electronics related apprenticeship when I started college in '75. Lucky for me, that was the start of my career as I became an intern sound engineer/stagehand within the university performing arts complex, working there for nearly a decade. Archiving the studied and practicing musicians, recorded to be juried in order to achieve their higher degree, was a favorite Mixing/Recording task, trying every studio grade mic on hand, in every position, to retrieve the most realistic sound from each instrument. The four performance halls and numerous rehearsal studios featured known performers, but most importantly, these "Soundman" experiences solidified my awareness of how live acoustical instruments should sound. Moreover, my preference for a stereo's 3D sound, with a significant sense of depth over presence from our speakers became an objective. Mono discs played back on our stereo systems can sound shockingly realistic, including elements of the 3D: Width, Height and Depth. Required is extremely balanced, Level output from each speaker, often re-adjusting the level balance with each disc...Then, there are some fantastic sounding, deluxe size, record players which can bring the sound "way out of the box."
However, Psychoacoustics is unique for each of us, and that is very okay. I studied psycho-acoustics for a few semesters, the ear to brain connections. Some music is better than none. Even a low fidelity recording, containing known music, but sounding distorted, can still elicit our ear-brain's ability to "recreate the proper playback sound within our minds." As crazy as this might sound, think of a conductor of an orchestra and each musician. Not all musicians have great sound systems BTW...
But, even a modest mono record playing system can surely bring on the joy of listening to music. 78 rpm playback, the most "forgiving" recorded media, instantly proves its worthiness thru a modest system and can present a dynamic range which overwhelms pre-conceived notions. Of course, with an excellent stereo system, including a mono phono preamp with the correct, vintage era, playback curves, AKA: accurate, switchable Phono EQ, Mono playback from one or two speakers is most enjoyable...