The Keeley Neutrino is an envelope filter pedal from Keeley Electronics, first shipped in 2014 and later updated as the Neutrino V21. An envelope filter, also called an auto-wah, sweeps a filter across your tone in response to how hard you pick: play harder and the filter opens up, play softly and it closes down. It is the effect behind much of the classic funk rhythm guitar sound, and it does the work of a wah pedal without your foot2.
The Neutrino is built on a compact analog circuit based on an opto-coupler, the light-sensitive component used in the classic envelope filters of the 1970s1. The V2 is described as 100% analog and made in the USA, and works for guitar, bass and keyboard3.
What the Neutrino does
Instead of a fixed EQ curve, the Neutrino tracks the envelope of your picking and moves a filter with it. Pedal of the Day's reviewer put it plainly: with the Gain set correctly, it "sounds like a wah pedal rocking back and forth, but without the extra effort on your part"2. How you attack the strings shapes the result, and the reviewer found that "the pick attack is key in getting the sound you desire, and the Neutrino does this superbly"2.
The middle selector knob chooses between three filters, and each has its own character2:
| Filter mode | What it does | Character |
|---|---|---|
| Low-Pass (L) | Cuts off the high end | Darker and muddier, while retaining clarity2 |
| Band-Pass (B) | Equal high and low cuts | The most vocal-sounding of the three2 |
| High-Pass (H) | Cuts off the low end | Cuts through the mix, brighter tonal quality2 |
The controls and the Range toggle
The Neutrino's control set covers input Gain, resonance Peak, the Filter selector, tone Range, and Drive direction1. The Gain control blends your signal in with the effect so the sweep tracks your playing cleanly2. The Peak knob sets how much wah is in the mix, "from a slight, warm, mellow tone coloring to a sharp, duck-like quack"2.
The Range toggle switches between HI and LO and adjusts which frequencies are stressed when picking2. On the V2 this appears as a Range Switch with HI or LO positions3. The Drive control sets the sweep direction, up or down34, and on the original pedal it sat in a side-mounted, recessed switch that kept the face of the pedal clean, alongside an internal output Volume control31.
The V2 and its opto-couplers
The V2, released in 2020, is a reworking of the pedal Pedal of the Day had reviewed almost five years earlier5. It keeps the same core layout, with three filter ranges, two directions, two frequency-center ranges and a Peak control5, but upgrades the parts inside. The design is based on an opto-coupler fine-tuned to sound smooth and vowel-like3, and in Sweetwater's demo, Don Carr noted the V2 uses "hand-selected opto-couplers, which are of an even higher grade than you'll find in a mint vintage original"4. A voltage-doubler enhanced power supply allows for extra headroom3.
"It's still the same amazing funk machine we all know and love, it just sounds…better."
What reviewers said
The original Neutrino earned strong praise: Pedal of the Day called it one of their, and many other players', favorite filters ever5. On the V2, the same site found the opto-couplers "particularly smooth, giving you an amazing vowel-like tone"5. In Sweetwater's video demo, Don Carr highlighted the pedal's range, saying "I really like how subtle and extreme this pedal can be," with a wide sonic palette that plays well alongside other pedals4. Robert Keeley himself likens the V2 to having "Jerry Garcia in a bottle"4.
In that demo, Carr also shows a quick route to a classic tone: straight out of the box, with the Range toggle set to Lo and every knob at 12:00, the pedal nails the elusive "Shakedown Street" auto-wah tone4.
Videos
Sweetwater
Keeley Electronics
Questions
How do you get the Shakedown Street tone on a Keeley Neutrino?
In Sweetwater's demo of the Neutrino V2, Don Carr found that straight out of the box, with the Range toggle set to Lo and every knob at 12:00, the pedal nails the elusive Shakedown Street auto-wah tone. From there you can fine tune the Gain, Peak and Filter controls to taste.
Is the Keeley Neutrino analog?
Yes. The Neutrino V2 is described as 100% analog, made in the USA, and built around hand-selected opto-couplers in its filter circuit. The original Neutrino also used a compact circuit based on an opto-coupler.
What is the difference between the Keeley Neutrino V1 and V2?
The V2 keeps the same core feature set: three filter ranges, two directions, two frequency-center ranges and a Peak control. It adds hand-selected opto-couplers of a higher grade than a mint vintage original, a voltage-doubler power supply for extra headroom, and a modern new look. Reviewers found it sounds better than the original.
Does the Keeley Neutrino work on bass?
Yes. The Neutrino V2 is described as an envelope filter and auto-wah for guitar, bass and keyboard, so bass players can use it directly. The Range toggle between HI and LO lets you shift which frequencies the filter stresses, which helps when tuning the effect to a bass signal.
Sources (5)
- Keeley Ships Neutrino Envelope Filter, Vintage Guitar magazine, 2014-04-23
- Keeley Electronics Neutrino Envelope Filter, Pedal of the Day (www.pedal-of-the-day.com), 2015-01-30
- Keeley Neutrino Envelope Filter V2, Delicious Audio, 2019-02-19
- Keeley Neutrino V2 Envelope Filter Pedal Demo, Sweetwater, 2019-12-02
- Keeley Electronics Neutrino Envelope Filter V2, Pedal of the Day, 2020-10-21
