The circuit is called Diefet. I can't seem to find a really good sample right now, but if you google it there are lots of guys that built this and posted samples. In my oppinion it captures the signature Diezel sound quite good, I don't know though how will it really compare to the real thing.
I built one once it sounded pretty good as far as FET preamp translations go.
this one was different though It wasn't an actual mock up of the preamp.
the diefet was the dr. boogey pedal which was a mock up of the Dual Rectifier pre amp with FETs.
the french guys who made the project took a vh4 and spectrally analyzed its response then they modified the dr boogey to have the same frequency centers and such.
Like all FET preamp based pedals they sound better than manufacturer stock offerings but are no competition for a tube amp.
I imagine that the power section it's run through will greatly affect the tone. Might sound accurate through a Diezel clean channel, but not so great on something else. Anyone done a direct comparison?