I've been involved with the design and manufacture of phono stages of both styles discussed here - standalone phono stages without line stages, and complete preamps with built-in phono stages as well as attenuators and line stages. Based on first-hand experience, it is possible to build top-notch (as in award-winning) phono stages using either approach.
Either way has its pros and cons. As is often said, it is the implementation that matters the most. Integrating everything together has the advantage of ditching the pressure-contact interconnect (via the problematic RCA/XLR connector) in favor of a superior hard-wired connection. However, keeping separate power supplies for every individual circuit nearly always sounds better (including separate transformers), and it is logistically easier to do this when the phono circuitry is unemcumbered by the line circuitry and vice versa, i.e., the circuitry being addressed is as simple as possible.
Of course, it is feasible to integrate the phono circuitry with line circuitry, keep completely separate power supplies and still stuff everything into one chassis for the signal circuitry and another for the power supplies, but to do this right would call for chasses that would normally be chosen for use with a good-sized power amp.
If I didn't have to think of the preferences and preconceptions of the audio market (but for whatever reason wanted to back away from the technically superior but commercially inferior solution of active loudspeakers), my preferred solution probably would be a minimalistic integrated power amp with built-in input selector and attenuator (with separate chasses for power supplies and signal circuitry), paired with separate phono preamp (no level control), and line buffer amps with neither level controls nor input selectors - one line buffer amp for each source (except phono). And everything built as a mono unit.
BTW, I wouldn't recommend combining the phono preamp together with the power amp. The sound of the turntable is too much affected by vibrations transmitted through the air and ground. For top performance the turntable should be in a separate room/closet isolated from the vibrations and air pressure from the loudspeakers. If you were to go with a combination phono/preamp/power amp together with the turntable in an isolated room, the speaker cables would likely need to be v-e-r-y long.
Unless you went with active loudspeakers, which would allow you to ditch the power amp and speaker cables.
regards, jonathan carr
