The Fredric Effects Grumbly Wolf is a combined distortion, fuzz, octave and ring mod effect in one pedal, made by Fredric Effects of London1. The circuit is an asymmetrical hard clipping distortion followed by an octave/ring mod stage, which means the pedal can cover a wide range: Fredric Effects describes it as "capable of everything from classic crunchy overdrive to intense octave fuzz madness"1.
How the pedal works
The signal path has two stages. First comes the distortion: an asymmetrical hard clipping circuit, meaning the waveform is clipped unevenly, which shapes the overdriven character of the note1. Second comes the octave/ring mod stage, based on the classic Green Ringer, which a toggle switch turns on and off1.
With the distortion turned up and the second stage engaged, Fredric Effects says the extra gain delivers "full-on splattery fuzz." With the distortion turned down, the same stage produces "clangy ring mod type sounds"1. That gives the pedal two distinct personalities from one switch: an aggressive octave fuzz voice, and a metallic ring mod voice.
The Green Ringer stage
The Green Ringer is a vintage analog octave-up effect. Premier Guitar describes it as a ring modulator circuit that was itself "inspired" by the earlier Ampeg Scrambler23. On the JHS Pedals channel, Josh has called it one of his all-time favorite sounds for manipulating frequency and the waveform, noting that the first version is rare and "totally gooped inside," its components hidden under epoxy4.
"The first version green ringer that nobody even knows exists. It's totally gooped inside."
FuzzHugger Effects, which builds its own octave-up pedal around the circuit, notes that the name "Green Ringer" may be a trademark of Dan Armstrong Effects, an unaffiliated company5.
The 15th Anniversary Special version
Fredric Effects also makes a 15th Anniversary Special version of the Grumbly Wolf that incorporates two entire distortion circuits1. The second distortion is enabled with DIP switches on the circuit board, which the maker describes as delivering "absolutely loads of gain"1.
The second distortion circuit in the 15th Anniversary Special is switched on with DIP switches inside the pedal, not a front-panel control, so it is a set-and-forget modification rather than something you toggle mid-song1.
Demo
A demo of the Grumbly Wolf by Christian at Magnetic Effects is available on YouTube and covers the pedal's range from overdrive to octave fuzz1.
For players comparing Fredric Effects distortions, the company also makes the Verzerrer and the Silicon Harmonic Percolator, alongside the Harmonic Percolator Interfax Spec.
Videos
Magnetic Effects
LongFallBoots
Questions
Can the Grumbly Wolf's octave/ring mod stage be turned off?
Yes. A toggle switch on the pedal turns the octave/ring mod stage on and off, so you can run just the distortion side of the circuit on its own, or add the second stage for extra gain and octave or ring mod sounds.
What is the Green Ringer?
The Green Ringer is a vintage analog octave-up effect, described by Premier Guitar as a ring modulator circuit that was itself inspired by the earlier Ampeg Scrambler. Fredric Effects bases the Grumbly Wolf's second stage on this classic circuit. The name may be a trademark of Dan Armstrong Effects.
What kind of clipping does the Grumbly Wolf use?
The distortion side of the Grumbly Wolf is an asymmetrical hard clipping circuit. Asymmetrical clipping, where the waveform is clipped unevenly on one half, shapes the overdriven character before the signal reaches the octave/ring mod stage.
Can the Grumbly Wolf do ordinary overdrive?
Yes. Fredric Effects describes the pedal as capable of everything from classic crunchy overdrive to intense octave fuzz madness, so with the octave stage backed off it works as a straightforward distortion pedal.
Sources (5)
- Grumbly Wolf distortion with ring mod, fredric.co.uk
- Mu-FX Octave Divider Review, Premier Guitar, 2015-06-09
- Builder Profile: The Mu-tron Story, www.premierguitar.com, 2013-09-12
- 3 New JHS 3 Series Pedals : Bit Crusher, Glitch Delay, Ring Modulator, JHS Pedals (YouTube channel), 2026-05-06
- FuzzHugger Upper frequency doubler / octave up, FuzzHugger Effects
