MXR M306 Poly Blue

The MXR M306 Poly Blue Octave is a fuzz, pitch-shifting and modulation pedal in one box. It gives you four separate octave voices with their own level controls, a switchable fuzz circuit, and a dual-mode modulation section that taps into Leslie/Phase 90-style effects depending on which pitch-shifting mode you select¹².

It is a reworking of the MXR Blue Box, the octave/fuzz pedal MXR has built for decades. Where the Blue Box drops your signal two octaves down and fuzzes it, the Poly Blue opens the circuit out into a four-octave, polyphonic pitch shifter with modulation on top¹².

What it does: octave, fuzz and modulation

The core of the pedal is pitch shifting. You get four separate octave divisions, each with its own level control: Sub-1 and Sub-2 for one and two octaves down, and Oct+1 and Oct+2 for one and two octaves up¹². That is a four-octave total range, so you can blend anything from a deep sub-octave rumble to a shrieking two-octaves-up squeal against your dry signal.

On top of the pitch shifting sits a fuzz circuit you can switch in and out, plus a modulation effect. The modulation is dual-mode: it taps into Leslie-style and Phase 90-style effects depending on whether the pitch shifting is running polyphonic or monophonic². In monophonic mode it provides swirls and swooshes that MXR says were inspired by the Phase 90¹.

The pedal is polyphonic by default, meaning it tracks chords rather than just single notes, and it can be switched to work in monophonic mode³.

The controls

The Dry control is worth a closer look: it blends your clean signal in with the shifted octaves, and when combined with a held press of the fuzz toggle switch it also acts as the volume level control for the fuzz circuit³.

Expression and tap switch options

The Poly Blue has an expression jack that opens up two ways to control it hands-free³¹².

• Expression pedal: connecting a TRS cable from an expression pedal into the Expression jack lets you crossfade between two different pedal configurations in the heel and toe positions³. Gearnews describes it as an expression output allowing expression pedal-operated control of various parameters¹².
• Tap switch: you can connect a regular tap switch into the expression socket and use it to switch the fuzz circuit on and off, or to change between polyphonic and monophonic mode³.

That crossfade trick effectively gives you two sounds in one pedal, swept with your foot, which partly makes up for the lack of presets³¹.

Based on the MXR Blue Box

The Poly Blue is an expanded version of the Blue Box, the octave/fuzz pedal MusicRadar called iconic³. Gearnews framed it the same way: MXR "takes their Blue Box pedal, and makes the circuit way more versatile"¹.

The original Blue Box is a much simpler animal. Its single OUTPUT control sets the overall volume of the effect, and it is powered by one 9-volt battery installed under the bottom plate⁴. It currently lists at $99.99⁵, roughly half the Poly Blue's launch price. The Poly Blue keeps the octave-and-fuzz concept but adds the four-octave pitch shifting, the modulation, the polyphonic tracking and the expression control, and it drops the battery: it runs from an external power supply only¹.

What reviewers said

Gearnews covered the pedal from announcement to a later verdict, and the two reports land very differently¹.

In an early note, the reviewer was blunt about the fuzz side of the pedal¹:

Gearnews, on the Poly Blue's overall tone¹

By the end of February 2022 the verdict had turned around completely:

Gearnews, comparing the Poly Blue Octave to the Boss OC5¹

The same reviewer's one regret was storage: "Shame you can't set up more presets because there's plenty of great sounds in there"¹.

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