Your publications (rare) are highly appreciated for their quality and pedagogy.
You explain unprejudiced the advantages and disadvantages of electrostatic headphone amplifiers using transformers step up behind a tube amplifier operating in OTL mode.
If I understand correctly, the theoretical performance of such an amplifier (with transformers step up) will always priori inferior to those of direct-coupled amplifiers do not use output transformers
While I appreciate your complement, there's a little misunderstanding going on here that is probably my fault. The transformer-coupled topology I was referring to (and use myself) is not the type employed by the Stax,Woo, or Verto boxes, where a low voltage, low impedance speaker level signal is stepped up to electrostatic headphone levels via an additional high winding ratio transformer. The transformers I use are very much like any other tube amp output transformer, except that the secondary winding is wound for a 1:1-1 ratio. Unlike Stax-type boxes, the high impedance of the amplifier output transformer primary is preserved, and there is no voltage step-up at all. All amplification is via the tubes, and the headphones are driven directly off the secondary of the amplifier output transformer.
Having never heard any transformer boxes except for the Stax, I'm not really qualified to render an opinion on them. I will say that the lower the winding ratio, the better the chance to build a quality unit. In a high level signal transformer such we're talking about here, as step-up increases, so does stray capacitance. The greater the stray capacitance, the greater the high frequency roll off. If you cut the primary turns to decrease the number of required secondary turns, you decrease the bass. A 1:5 step-up sounds a lot more promising than 1:50.
Edited by FrankCooter - 10/28/14 at 6:09pm