Years ago Matt from Stomp Under Foot bought some original, NOS LM308 Op-Amps that were used in the original Rat pedal.
Around the same time, he received a very rare, first-edition Bud Box Rat to repair.
The Bud Box Rat was originally supposed to be just the one run of twenty-five pedals and never to be made again but people liked them so much that there were some slight changes made and then they were produced as, what is now known as, the Rat.
The Skinner Box is based on the rare, prototype "Bud Box" Rat and is made with the discontinued, original, new-old-stock LM308 Op-Amp.
The LM308 in this circuit gives you that original sound you can only get with the vintage pedals.