flea/head phone amp all DHT

[glen]

It seems all the small 45 level SET's we see have indirect heated gain stages.

I built a typical WE417A SET (5k:32 OPT) for my Grado headphones that I absolutely love, the sound is like no other headamp. It has a shunt B+ and is dead silent with these 98 db per mW phones.

But I am ready to try a DHT headamp. With the availability of inexpensive tubes like the 4p1l and the 6C4C, I can't help but wonder why we rarely see an all DHT amp.

I want to explore ortho headphones which aren't as forgiving w.r.t. damping factor as Grados, so the DCR of a 32 ohm secondary can be a hurdle. But if I imbark on this project I would need more power than my little spud SET that maxes out around 0.7vrms (15 mW).

Goal for this all DHT SET headamp would be about 4Vrms into 32 ohms ( 0.5W) with an output impedance at least under 10 (including secondary DCR.)

The options are too many for me to decide. 4p1l to 4p1l to singlefeed electraprint 5k:32. Or possibly 4p1l to 6C4C parafeed to Magnaquest 5k:16. Also considering maybe a #26 for the gain stage instead of the 4p1l.

As far as hum/noise I have 4 sets of coleman regulators and Salas shunts which are dead quiet and am familiar with suspension techniques for microphonic tubes.

My problem is chosing between parafeed and singlefeed and the transformer choices for headphones are limited. Especially with the new ortho headphones it is not as easy as first glance, for example 0.5W into a 32 ohm headphone, can be the equivalent voltage swing of 2W into 8 ohms depending on the transformer ratio.

Probably the biggest bang for the buck would be 4p1l rc coupled to a 6C4C parafeed magnaquest 5k:16.

Any advice on direction from those more experienced than I would be appreciated?