Check out Forssell Technologies. Schematics there.
I have built several based on his design that work very well.
It is based on discrete Jfet Modules that are made by several sources including John Hardy, API and the above reference. It has a balanced transformer input and DC servo output stage.
If you are interested I can provide all you need for putting one together. Go here for pic of what I built at www.kbaudio.imajon.com
Have fun and good luck
