This guitar wah wah circuit uses a filter which can be manually swept across the middle of the audio frequency range.
      A single pole, voltage- controlled, low-pass filter can be constructed using a CA3080 as a current-controlled resistor.
      A simple k)w-pass RC filter configuration is used, the controllable ‘R’ is the CA3080 and the ‘C’ is C1. This circuit configuration would normally be a slew limiter, except that the signal level is kept deliberately low (Ri and R2 form a 100:1 attenuator) so that the IC operates in a linear mode. This enables it to look like a variable resistor, which when varied, varies also the break frequency of the filter.
      By applying positive feedback around the filter (R6,C2) it is possible to produce a peaky filter response. The peak increases with frequency, producing the wah wah effect.