The Electro Harmonix Q Tron Plus Envelope Filter Pedal takes all the features you know and love about the original Q Tron and adds both an effects loop and a attack response switch.
The Effects Loop lets you place an additional effect between the Q Tron 's preamp and filter section without changing the envelope drive. The added Response Switch selects between a slow, smooth, vowel-like attack and the fast, snaked response of the original Q Tron.