The topology of the amp is a simple grounded cathode gain stage coupled through a capacitor to an opamp wired in unity gain mode. The standard SOHA uses LND150 depletion mode MOSFETs for the CCS for reasons discussed below. The amplifier circuit is, thus, very simple.
http://headwize.com/projects/cavalli2_prj.php
JT-11P-1 Balanced Tube Line Input Stage.
http://www.jensen-transformers.com/as/as088.pdf
The point of star grounding is to keep signal circuits with NO common mode noise rejection (that is, all the normally used tube gain stages) from picking up current-induced noise from other currents running through a shared ground. Obviously, the most critical stage is an input stage, and the closer you go to the output stage, the bigger the signal level and the less the milli- and micro-volt signals in the shared ground will be.
http://www.geofex.com/Article_Folders/stargnd/stargnd.htm
The single tube configuration is the longing of any audio designer, and here we could have only one tube per channel. If we have only one tube on the signal the distortion spectrum will be a perfect decay on all harmonics, so it sounds very natural.
http://headwize.com/projects/showfile.php?file=ciuff4_prj.htm
The tube or the power transistor is loaded directly by the speaker (often thru a transformer, fro impedance matching!), and is biaised at the current necessary for full modulation (that means a maximum power dissipation for no input signal).
http://www.recherche.enac.fr/~puechmor/e_aclass.html
The need for a high-gain stereo preamp has diminished, because the CD has replaced the LP record in most audiophile homes.
http://headwize.com/projects/showfile.php?file=barbour_prj.htm
Preamp with Relay-Based Input and Power Switching
http://headwize.com/projects/showfile.php?file=ahammer1_prj.htm
15 Watt Audio Tube Amplifier Schematic Diagram
http://www.freeinfosociety.com/electronics/schemview.php?id=1066