Check the listing for details. Electro-Harmonix Micro Q-Tron Envelope Filter Pedal. Condition: Used. Listed at 101.25 USD. Classic Auto-wah Effects Made Easy If you're a player with an affinity for classic auto-wah sounds, but you prefer streamlined controls, you'll dig the Electro-Harmonix Micro Q-Tron. This stompbox is powered by an internal envelope follower, which analyzes the dynamics of your playing to determine the intensity of the wah effect. When you pick harder, you'll get a wider frequency sweep; when you pick more softly, you'll produce a subtler sound. And It's a breeze to dial in — a few twists of the Micro Q-Tron's three knobs is all that stands between you and all the funky, Garcia-style quack you can handle. The Micro Q-Tron features true-bypass switching, and it's housed in a rugged, road-ready die-cast chassis that's compact enough for even the most crowded of pedalboards.