The Keeley Neutrino is a funky, tripped-out envelope filter and auto-wah. Its dynamic wah sounds closely react to your pick attack, so the harder you pick, the harder it "wahs." The 100% analog Neutrino uses opto-couplers specifically chosen to deliver smooth, vocal-like tone.
While the controls are relatively simple, the Neutrino provides a ton of flexibility, which results in a versatile palette of different sounds. The Filter Band knob selects what pass band filter is used. Low Pass (L) allows low notes to pass and cuts the high ones. Band Pass (B) trims both highs and lows and allows smooth midrange to pass through. High Pass (H) cuts lows and sets the pedal to operate at high frequencies. From there, the Range switch further adjusts the operating range of the variable filter—"Lo" emphasizes lower registers, whereas "Hi" accentuates higher notes.
The Gain control is pretty straightforward—it controls the input level of the circuit, so you can adjust how hard your guitar hits the front-end of the pedal. And Peak is pretty, simple, too: it controls the filter frequency. As you turn the Peak knob up, you'll get more resonance, and turning it down gives you mellower wah sound. Most interesting, though, is the "Direction" control hidden on the side. This flips the direction the filter moves. It's similar to the direction you move a wah pedal after you pick the note.
This 2018 Keeley Neutrino is in excellent all-around condition. It shows some signs of use, and it has some velcro installed on the bottom, but it's free of severe cosmetic dings or issues and functions 100% as it should. Plus, we have the box!