While I would never claim that line stage preamps are
interchangeable, I agree with Kevin Deal where he indicates that most of the
top preamps sound pretty good. Roger
Modjeski, when addressing my audiophile society, noted that high quality line stage
preamps are something that manufacturers should have under control, the
principles being well understood.
One of the posters above asserted repeatedly that the top of the line PrimaLuna preamp generates considerable second harmonic distortion. I have not seen any measurements to back this up. If anyone has a reference, please post it. Stereophile very recently reviewed the ProLogue Premium preamp, measuring primarily second harmonic distortion ranging from 0.1% to 0.31% depending on output level. This preamp has a list price of $2,199 and is not the top of the line model.
I own the Dialog Premium Preamp, the current top of the line, which I bought used from a private party. I use it single-ended into a Pass Labs XA30.8 power amp. This combination works great and sounds fantastic. The preamp is dead quiet, with no hum or noise, and the stock tubes are very neutral. Is the DPP state of the art? I’m honestly not sure if that is my objective. But from my perspective this preamp is flawless and I do not plan to replace it for a long time.
I did try vintage Philips rectifier tubes, but didn't continue with them because in my system the resulting sound has a bit too much of the warmth traditionally associated with tubes. Some people love this type of sound but it ultimately comes down to preference.