The Keeley Neutrino Envelope Filter V2 is an analog envelope filter and auto-wah pedal from Keeley, aimed at guitar, bass and keyboard players1. An envelope filter, sometimes called an auto-wah, listens to how hard you pick and sweeps a filter in response: play harder and the filter opens up, play softer and it closes down. You get the vowel-like quack of a wah pedal rocking back and forth, but without working the pedal yourself.
What sets the Neutrino apart is its circuit. The design is based on an opto-coupler, a light-dependent component that Keeley fine-tuned to sound smooth and vowel-like, the same class of component behind the classic funk filters of the 1970s1. The V2 is 100% analog, made in the USA, and built in what Delicious Audio called "an incredibly tough build" meant to last for decades1.
The controls
The Neutrino V2 gives you three filter ranges, two directions, two ranges for the frequency center and a Peak control2. Each control does one clear job:
| Control | What it does |
|---|---|
| Gain | Sets the input sensitivity, so the filter responds to your picking strength; blends dry signal with the effect for a seamless joint3 |
| Peak | Sets how much "quack" there is, or how smooth you roll1 |
| Filter Selector | Chooses between three filter types: High-Pass, Low-Pass and Band-Pass1 |
| Range Switch | HI or LO, adjusting which frequencies are stressed when you pick13 |
| Direction Switch | Up or Down, controlling which way the wah sweeps13 |
| Volume | External output Volume control on the side of the pedal2 |
The three filter positions each have their own character. In Pedal of the Day's review of the original, the Band-Pass position was "the most vocal-sounding of the three," the High-Pass "cuts through the mix, and gives off a brighter tonal quality," and the Low-Pass is "darker and muddier, while retaining clarity"3. The Peak knob spans a wide range too, from a slight, warm tone coloring at one end to a sharp, duck-like quack at the other3.
The Gain control is the one to spend time with first. Because it sets how hard you have to play to trigger the sweep, it is what makes the pedal work on bass as well as guitar: a bass puts out a hotter signal, so backing the Gain off keeps the filter from slamming open on every note4.
History and versions: from the original Neutrino to V2
Keeley introduced the original Neutrino Envelope Filter as a compact opto-coupler envelope filter pedal with true-bypass switching, controls for input Gain, resonance Peak, Filter selector, tone Range and Drive direction, plus a side-mounted, recessed Drive switch and an internal output Volume to keep the look clean4. Pedal of the Day reviewed and demoed that original version in January 20152.
The V2 arrived as a new version of the same pedal, reviewed by Pedal of the Day on 21 October 20202. The changes were focused rather than a redesign:
- Improved note tracking2
- Upgraded components2
- The internal output Volume control moved to the outside, on the side of the pedal2
- A voltage-doubler enhanced power supply for extra headroom1
That voltage-doubler is worth noting for anyone comparing the two versions. Pedal of the Day explained that Keeley "even engineered a power supply voltage-doubler so you maintain the highest headroom for your tone," meaning the pedal internally doubles the 9V coming in so the filter circuit has room to swing without clipping2. Everything else carries over: the same three filter ranges, two directions, two frequency-center ranges and Peak control2.
What reviewers said
Reviewers on both sides of the V2 divide have been positive. Of the original, Pedal of the Day's Mike B wrote23:
"Right off the bat, it oozed that classic MuTron, 'Jerry' envelope filter sound, but in a way that was not overbearing, and added just the right amount of color to my tone."3
Mike B, Pedal of the Day3
That Mu-Tron comparison comes up naturally because the Neutrino uses the same opto-coupler approach as the vintage filters players associate with that sound. The same review called the Neutrino a pedal that "does as good (if not a better)" job of bringing the funk than other envelope filters3.
The V2 review was just as warm. Pedal of the Day called the original "one of our, and many other players' favorite filters EVER," and said of the V22:
"it's still the same amazing funk machine we all know and love, it just sounds…better2."
Pedal of the Day3
They described it as "a wonderful little box chock full of funk"2.
Videos
Sweetwater
Keeley Electronics
Mike Hermans
Questions
What changed between the Keeley Neutrino V1 and V2?
The V2 keeps the same core design, three filter ranges, two directions, two frequency-center ranges and a Peak control, but adds improved note tracking, upgraded components and an external output Volume control on the side of the pedal. The original had its output Volume control mounted internally. A voltage-doubler power supply also gives the V2 extra headroom.
Does the Keeley Neutrino work on bass?
Yes. Keeley positions the Neutrino V2 as an Envelope Filter and Auto-Wah for guitar, bass and keyboard, not as a guitar-only pedal. The Gain control sets how hard you have to pick to open the filter, which lets you match the pedal to a bass's stronger output.
Is the Keeley Neutrino true bypass?
Yes. Both the original Neutrino and the V2 use true-bypass switching, so your dry signal passes through untouched when the effect is off. The V2 runs on 9 VDC at 25 mA.
How much current does the Keeley Neutrino V2 draw?
The Neutrino V2 draws 25 mA at 9 VDC. Its voltage-doubler power supply internally raises the voltage to maintain high headroom, so a standard 9V center-negative supply covers it.
Does the Neutrino sound like a Mu-Tron?
Reviewers have drawn that comparison. Pedal of the Day's review of the original said it oozed the classic Mu-Tron, Jerry envelope filter sound, but in a way that was not overbearing. The opto-coupler design is the same approach that made those vintage filters smooth and vowel-like.
Sources (4)
- Keeley Neutrino Envelope Filter V2, Delicious Audio, 2019-02-19
- Keeley Electronics Neutrino Envelope Filter V2, Pedal of the Day, 2020-10-21
- Keeley Electronics Neutrino Envelope Filter, Pedal of the Day (www.pedal-of-the-day.com), 2015-01-30
- Keeley Ships Neutrino Envelope Filter, Vintage Guitar magazine, 2014-04-23
