Sound of transformers in preamps?

The Dude has a power transformer, but is not transformer coupled. To answer the posters question, yes the transformer can and does certainly influence the sound of a preamp. Depending on the design of the preamp transformers can be used in several locations. They can and must used in the power supply, can be used as chokes in the power supply and some use them for coupling.

In each instance the transformer can and does impact the sound regardless of use or location.

Also, wether or not a transformer coupled preamp sounds best etc... I have no idea. I think a skillfully designed transformer or capacitor coupled preamp will yield beautiful results. The transformer quality as well as the cap quality in that position is vitally important. I do know this :-)