Originally Posted by msjjr
I don't know if this is relevant to your point, and I must add I a not an engineer, but the Stax is easier to drive than the HE-90's with my amp, ie louder sooner. The hybrid 300 B's and the HE-90's are audio heaven for me.
I'm not an engineer either but that's no excuse... It's strange that the Stax would be more sensitive on your amp since the HE90 is far more sensitive with everything being setup properly. Something must be very wrong with the headphone bias to get that effect.
Originally Posted by FrankCooter
I'm curious about your 300B design. The problem, as you mention is an appropriate output transformer. The custom single-ended Electra-Print transformers I own have a 1:2 step-up with a 3K primary. According to Jack Elliano, this was about the maximum feasible step-up ratio possible without either reducing the primary impedance or sacrificing bandwidth. This works fine with an EL34 or 6550, and the 3K load is standard for a 300B. The big problem is the low mu of the 300B. A 1:2 step up with a 300B doesn't provide enough voltage gain or swing to really drive electrostatic headphones.
I'm going to start off with the Ciuffoli design pretty much stock (except the bias supply since I'm not a fan of burning up my diaphragm coatings) and see how it works. 1:2 really isn't enough and the Ciuffoli amp isn't that much better at 1:2.25 but the Lundahl iron is cheap enough to play with. What I really should be doing is building KG's insane all DHT, fully balanced 3 stage beast (so 12 DHT's in a single amp, AD-1's, 300B's and 845's) but I don't really feel like dropping 6k$ on just the parts....
Now I'm going back to figuring out how I'm going to build the smallest, self contained Stax amp I can. Think Egmont in a SRD-7 box...