Regarding the 8 db spec difference in S/N ratio between the VTPH-2 and VTPH-2A that George pointed out, I can say that one thing which has particularly amazed me about my VTPH-2 is how quiet it is. In fact when I listen with my Stax electrostatic headphones and no music is playing I hear absolutely nothing even with the volume control on the Stax amplifier at max (which is **way** higher than I would ever set it while listening to music). (With speakers I do hear some slight noise at high volume settings if I get close to the speakers, but that is clearly being introduced elsewhere in the system).
I see that the 80 db spec for the VTPH-2 is accompanied by the words "noise level will be tube dependent." Perhaps the 88 db spec for the 2A simply reflects a change Keith made in his choice of tube manufacturer at some point in the evolution of the design, and/or a change in the criteria he applies in the tests I assume he performs to weed out noisy tubes.
Best regards,
-- Al