The ES-1 doesn't add anything new except a higher pricetag. It is basically the third take on the T2 concept with a direct coupled driver stage, AC coupled to the output. I'm sure many people will like the sound as many like the Sennheiser stats but my ears aren't as forgiving.
Not really true. The T2 was a tube/solid state hybrid. The T2 was fully
direct coupled input to output. The ES-1 is in fact similar to the
stax sr-x circuit with much bigger tubes and higher voltages.
This circuit does have a direct coupled output, but does have
interstage coupling caps.http://www.bonavolta.ch/hobby/en/audio/hdgsta.htm
There is absolutely no way that omega2 headphones can tolerate
anything more than about 650 volts of bias. They would destructively
arc and be completely destroyed.
You could in fact build an amplifier with a higher voltage swing up
to the max of 1200 Vpp stator to ground. You would get about 4 db
more volume than a BH. There are a number of tubes that would
work great for this. They are all bigger than an 6ca7.
The masters amp looks very much like a number of other push pull ultra-linear
designs. Probably sounds very good. The stax output jack is wired to the primary
of the transformer, same place the plates of the tubes are wired. Then a bias
circuit is added. Direct coupled output when wired this way. This is going to sound
very different from most of the other stax amps.