Mono block Preamp

Coincident Statement linestage is true dual mono, to get all those parts into one chassis would require it to be quite large and affect performance, what with emi/rfi. Two chassis, one control unit, signal path only, other for power supply. I think this better configuration vs power supplies in both chassis, just for the emi/rfi alone.  The two mono volume selectors can be a pain, and no remote available.

There are several mono phono stages.

I believe Conrad Johnson offered a complete dual mono preamp which came in 4 cases.

Typically a two box solution will be separating the power supply and amplifier section. Since a preamp is amplifying at such low levels I think designers felt they got more bang for the buck by getting the high voltage stuff away from the low voltage stuff.

Esoteric makes one-dual power cords need