This one is the Best preamp ever although I still need to build the SP13 and compare it also.
I have built over a dozen Transcendent Sound Ground Grid preamps. It is an excellent preamp in its own right, however I have concluded that no matter what you do to the GG it is bettered by the SP14.
Any future preamp builds will be SP14s. The SP14 is the king. Better definition, seperation and much better response, especially in the lower frequencies.
See it here: