Check the listing for details. ELECTRO-HARMONIX Q-Tron Plus Envelope Filter. Condition: New. Listed at 226.21 USD. Same design as the original Q-Tron, but with an extremely useful effects loop and an attack response switch. The effects loop gives the musician the ability to place an additional effect or chain of effects between the preamp and filter section of the Q-Tron Plus without changing the envelope control. This is particularly important with most distortion devices as most of them do not have an amplitude envelope. The FX loop also stimulates your creativity to try out all possible combinations in the effects loop: Try the Micro POG with a Deluxe Memory Man. You can invent all kinds of novel effects. The added response switch selects between a slow, smooth, vocal-like attack and the fast, meandering response of the original Q-Tron. All of our items have a 30-day return policy without explanat.