This is a Fender MD20 Mini Deluxe amp that has had its guts removed and replaced with an attenuator. Plug the Whoa-Yo in between your amplifier and your speaker to crank the amp while turning down the volume. I use it in my Fender Deluxe Reverb so that I can take the amp into overdrive territory without waking up my neighbors. Note: The MD20 no longer works as an amplifier with this modification – this is only an attenuator, but it looks cool.