Off of the Bottlehead website:skill level 1
As soon as we finished designing the original S.E.X. (Single Ended eXperimenter's) amp kit, we knew we needed a line stage preamp to go before it. What else could you call this kit but Foreplay?
Inspired by a design from George Wright, The $149 Foreplay is a line stage with dual mono volume controls, three pairs of inputs and a single pair of outputs."
Maybe I took this too literally, but Doc seems to gives credit to Mr. Wright.