The diode switching in this is unusual. It has 7 diodes in the feedback loop plus a germanium to ground after the output of the first opamp stage which are controlled via the switch. In one position you have 2 + 2 anti-parallel silicon diodes in the loop to give you a common symmetrical clipping that you have seen before. In the centre off position you get 4 + 3 anti-parallel silicon diodes in the feedback loop which gives you asymmetrical clipping, and in the other position you get the 4 + 3 again, plus a germanium diode to ground after the first stage.
On top of that you also have the Dynamics pot which can bring 2 more germanium diodes, 1 + 1 anti-parallel, gradually through the sweep of the pot.
Lots of clipping options there!
Burn is the drive control, the Tone control is a simple low pass filter before the second stage and you then have further Bass and Mids trimmer controls on the board. The other trimmers are for Presence and Note Shape.
Anyway, here's the interesting bits that Mr Barber writes about his original:
Three way toggle- This new control allows three distinct styles of symmetry to allow a perfect mate to your amps character.
8 knob control for tonal versatility-The Small Fry uses eight (including internal trim pots) control knobs as follows, Volume, Tone, Dynamics and Burn. Internal controls for Note shape, Bass, Midrange and presence. These controls allow the Small Fry to produce sounds ranging from sweet subtle sustain to smooth singing California amp style tones!
Unique controls- The note shape allows you to adjust your sound from tight and focused to a big round vintage tone, The dynamics control has earned a great reputation over the years for setting the transfer to smooth singing overdrive or raspy growling deep dynamics, continuously!
Barber adjustable phono style recovery stage- Most of our op-amp based overdrive pedals use a cool old style phonograph circuit to recover the frequencies lost in the overdrive stage, this worked great for vinyl and now works great for guitar overdrive!