[Keyboardist Gakushi’s Review] Warm Audio Mutation Phasor II - In-Depth Breakdown of a 1970s Electro-Optical Phaser

Intro

This time, I’m reviewing the WARM AUDIO Mutation Phasor II.
It faithfully recreates the swirly, psychedelic tones inspired by the Mu-Tron Phasor II, using a fully analog circuit.
Is it suitable not just for guitar but also for keyboards? We'll dive into its usability, tonal range, and more to find out.

Basic Information / Specs

• Product Name: Mutation Phasor II
• Manufacturer: WARM AUDIO
• Effect Type: Analog / Electro-Optical Phaser (Rate, Depth, Feedback)
• Release Date: Around June 2023
• Price: ¥23,800
• Main Features:
  • Uses RC4558P op-amps, vintage-style resistors, and film capacitors
  • Equipped with a Feedback knob for self-oscillating phase effects
  • Size: Width 3.5″ × Height 2″ × Depth 6.5″ / Weight: approx. 2 lb (about 900g)
  • Supports 9V DC center-negative or battery power (screwdriver required for battery replacement)
  • Buffered bypass design

Impressions After Trying It Out (Sound)

● Rate (Speed)

Dialing it to around 10 o’clock already gives you a fast, swirling motion. Below that, you get a vintage, Magnatone-style rotary-like modulation.

● Depth (Intensity)

At lower settings, it delivers a subtle phase effect. At higher settings, it produces a unique, paper-like swirling texture.

● Feedback (Resonance)

It enhances that classic '70s vibe. With low speed and high feedback, you get a Leslie-like sound. At higher speeds, it shifts into a metallic, humming-like tone.

● Overall Sound Impression

• From swirly/dreamy to psychedelic/funky, the tonal range is broad. It’s highly musical, with a deep, rich resonance.
• While it’s great for guitar, it particularly shines when paired with synthesizers and keyboards.

Usability & Handling

• The vertically aligned knob layout is intuitive and easy to operate. The controls are highly responsive, making it ideal for precise fine-tuning.
• Be mindful of space when mounting it on a pedalboard, as battery replacement requires a screwdriver and the unit is fairly large (approx. 7 cm × 17 cm).
• The buffered bypass helps prevent signal degradation.

Comparison with Other Models

• Original Mu-Tron Phasor II:The design stays very faithful to the original, with modern conveniences like battery operation thoughtfully included.
• Electro-Harmonix Small Stone / MXR Phase 90: Compared to these, the Mutation offers a more musical and wider-range phasing experience that’s capable of experimental, non-traditional modulation. It goes beyond typical phase effects to provide a deeper phaser experience.
• Versus Aguilar Grape Phaser (for bass): The Mutation delivers a smoother, more refined low-end response.

Who Is This For?

• Those looking for a psychedelic or dreamy-style phaser
• Players who want deep modulation for synths or keyboards
• Anyone who’s interested in a phaser with experimental qualities and rich resonant tones
• On the other hand, it might not be the best fit for those who prefer compact, lightweight pedals or prioritize simple operation.

Overall Summary

The Mutation Phasor II lets you experience the rich, swirly phasing sound of the classic 1970s Mu-Tron style with modern build quality.
It combines musicality, psychedelic character, and experimental spirit; all at an attractive price point.
I highly recommend it for those looking to master spatial modulation effects or add lush movement to synth textures.

Video

For this Mutation Phasor II demo, I recorded with both a Rhodes and a Clavinet.

Mutation Phasor II+RHODES

Mutation Phasor II+CLAVINET

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