Doug Self published a full-fledged preamp design in Volume 5. The design features a sophisticated tone control system. Tone controls have all but disappeared from commercial equipment as implementations were not always high enough quality. However, tone controls can help to improve the sound in your listening room allowing to slightly correct for speaker and room influences, or to slightly change a recording's tonality. Douglas embarked on a design with an absolutely transparent tone control system, and while he was at it, a very sophisticated excellently tracking volume control inspired by the legendary Peter Baxandall.
Naturally, interest was hight at diyaudio.com and Carl Huff took upon him the organisation of a Group Buy for the pramp PCB. He also added an 'enhanced I/O' board allowing the selection of several sources with high-quality hermetically-sealed reed relays.
All in all, the documentation is a sizeable package, and I offered to host it here, and update it when any changes are made. So by downloading this package you will be sure to have the latest version.
Have fun building, enjoy listening!