Used Electro-Harmonix Micro Q-Tron
The Electro-Harmonix Micro Q-Tron is an easy-to-use, true bypass, smooth envelope filter pedal that will funk up your guitar tones. An internal envelope follower analyzes the volume and dynamics of your playing to sweep the center of the filter for very wah - like tones that change as you play. A stronger attack or louder note will produce a wider frequency sweep while softer playing produces more subtle effects. Three simple controls allow you to easily dial in the perfect filter, with enough diversity to find the sound you've been searching for. You can easily power the Q-Tron by using a standard 9 volt negative center power supply or 9 volt battery.
Mode - Sets the mode of the filter (low pass, band pass, and high pass).
Q - Controls the bandwidth, from smooth to funky!
Drive - Controls the sensitivity and filter sweep range.