Here's the description from the Fairfield Circuitry website;
"Have you ever sat in a barber's chair wishing your tone was as slick as your freshly shaved upper lip? With the Barbershop Overdrive on your pedalboard, you could keep your moustache and sound good doing it.
The Barbershop is an original design, not a clone.
Raw, gritty, warm, smooth, open and transparent are all terms that have been used to describe this overdrive. It sounds great with any setup, but truly shines when used to dirty up a tube amp."
Here's the customary ProGuitarShop demo video of the Barbershop Overdrive in action;
Not only are Guillaume's designs interesting they are also well thought out and manufactured to a great standard. Here's a gutshot for the Barbershop Overdrive (check out the cool logo on the PCB!);
So, without further rambling (and with thanks to WhiteKeyHole and Guillaume) here's a schematic of the Fairfield Barbershop Overdrive;
So what have we got? It's two cascaded Jfet gain stages followed by a simple NPN transistor emitter follower. The mosfet device is there for polarity protection. The 10kB pot is the "Sag" control that affects the overall supply voltage to the circuit and the clipping in the cascaded jfet/emitter follower stages. Guillaume has suggested that he sets the bias of the two jfets at around 2/3 of the supply voltage (when measured at the jfet's drain). I'd replace the drain resistors with 25k trim pots which will allow you to dial in the 6.66v bias point a little easier than using trial and error with set resistors.
If you want to build one of these up you're going to need a vero layout, there's one available here; http://tagboardeffects.blogspot.co.uk/2012/06/fairfield-circuitry-barbershop.html, at IVIark's brilliant tagboardeffects blog.
Here's another vero layout for you;
Check out the forum topic on freestompboxes.org, Guillaume offers some really great info and tips to guys wanting to build the circuit up; http://freestompboxes.org/viewtopic.php?f=7&t=4435