Korpa 
This Cry Baby Wah combines convenient auto-return switching with circuitry specifically optimized to keep your low end fundamental intact.
This pedal can be powered by a 9-volt battery, a Dunlop ECB003 9-volt adapter, or the DC Brick™, Iso-Brick™, and Mini Iso-Brick™ power supplies (not included).
The Long Story
The first wah pedal designed by bass players for bass players. The 105Q incorporates a proprietary potentiometer and custom EQ circuitry specifically optimized for bass frequencies. The Cry Baby Bass Wah applies the wah effect to the mids and highs only, leaving a strong fundamental to hold down the bottom so you can take solos or throw in fills without ever disturbing your low end.