lewm,
this is the 1st time you have explained this and 1st time said I was wrong. If so, I thank you for the correction, however, what I hear is ....
My McIntosh mx110z has a Mode Switch,
I have Stereo and Mono LP’s, and Stereo and Mono Cartridges ready to play. I can play with all 3 arms engaged, and near instantly compare a,b,c with the front switch and MC setting or Pass, some volume differences, I make temporary pencil marks.
My friend Jim, met him here, is coming Thursday, I will wait for him, hear what we hear, old and new Mono LPs