Wah effect

A wah-wah pedal (wah pedal) is a type of guitar effects pedal that alters the tone of the signal to create a distinctive effect, intended to mimic the human voice. The pedal sweeps the peak response of a filter up and down in frequency to create the sound (spectral glide), also known as "the wah effect." (Effect Tone type)
The first pedal ever created was by Warwick Electronics Inc./Thomas Organ Company in November 1966; this pedal is the original prototype wah-wah pedal made from a transistorized MRB (mid-range boost) potentiometer bread-boarded circuit and the housing of a Vox Continental Organ volume pedal.
he creation of the wah-wah pedal was actually an accident which stemmed from the re-design of the Vox Super Beatle guitar amplifier in 1966. Warwick Electronics Inc./Thomas Organ Company had bought the Vox name due to the brand name's popularity and association with the Beatles. Warwick Electronics Inc. also owned Thomas Organ Company and had assigned Thomas Organ Company to create a new product line called the all-electric Vox Amplifonic Orchestra, the project was headed by musician and bandleader Bill Page.
While creating the Vox Amplifonic Orchestra, the Thomas Organ Company needed to re-design the Vox amplifier into a transistorized solid state amplifier, rather than tube, which would be less expensive to manufacture. During the re-design of the USA Vox amplifier, Stan Cuttler, head engineer of Thomas Organ Company, assigned Brad J. Plunkett, a junior electronics engineer, to replace the expensive Jennings 3-position MRB circuit switch with a transistorized solid state MRB circuit.