If all the source signals are at line level (which means that any TT has its own outboard phono preamp) a separate box called a "preamp" really makes no sense. It costs very little to build the selector switch and volume control into the power amp, and perhaps add a gain stage. As a bonus, this eliminates an interconnect. In theory it ought to be better than separate units.
The idea of a separate preamp derives from the days of hum-prone tube circuits. A high gain phono stage on the same chassis as a hefty power supply was asking for trouble.
The idea of a separate preamp derives from the days of hum-prone tube circuits. A high gain phono stage on the same chassis as a hefty power supply was asking for trouble.