Crazy Tube Circuits Phi V2

The Phi V2 is a compressor pedal from Greek maker Crazy Tube Circuits, first released in October 2021. What sets it apart from most compressor pedals is that it holds three separate, all-analog compression circuits, FET, OTA and optical, and you choose between them at a toggle switch¹². Each circuit is totally independent, with its own voice and different compression characteristics, range and response of controls³².

The pedal covers a wide range of compression ratios, from 1:1 to 20:1, and its Blend knob lets you mix compressed and clean signal for parallel compression, a studio technique Crazy Tube Circuits says brings "clarity and precision only found in studio recordings"¹. MusicRadar's Jonathan Horsley reported that the V2 "uses parallel compression for studio-quality sounds, has a low noise floor"⁴.

Three analog compressors in one pedal

Most compressor pedals build one gain-reduction circuit and shape everything around it. The Phi V2 instead gives you three, and the differences between them are the heart of the pedal. Gearnews described it as "a studio-grade compressor in a compact stompbox format"⁸, and Guitar World called it "a three-circuit, all-analog unit"⁹.

Because each circuit is independent, switching between them changes more than a voicing preset: the range and response of the knobs themselves differ from mode to mode³². Pedal of the Day's reviewer put it simply: "The three modes present in the φ (Phi) Golden Ratio v2 each have their own compressed voice"⁶.

FET, OTA and Opto: how the three circuits differ

The FET mode is the colored one: Crazy Tube Circuits says it "adds a distinctive color to the signal and can be set for super-fast response, but it may also introduce a bit of musical distortion"¹. If you want a compressor that also imparts character, that is where it lives.

The OTA mode is the tightest. Its feed-forward detector circuit can "squeeze" things harder, which the maker says makes it ideal for catching fast transients and limiting, and it is "the most controllable circuit with punchy and direct sound"¹. Guitar World noted the OTA "takes inspiration from mainstream guitar compressor technology"⁹, the family of chip-based compressors many players already know.

The OPTO mode is the smoothest. It is built around a hand-selected photocell combined with a feed-back detector circuit, which gearnews reported gives "a very studio quality-like smooth attack and release"⁸. Optical compression, the type found in classic studio compressors, is often chosen for its gentle, transparent action.

The controls and the blend

The V2 carries six knobs plus the circuit toggle⁹⁵:

• Volume: sets the output level⁴
• Blend: mixes dry and wet signal, from the clean original to fully compressed⁵³
• Ratio: 1:1 to 20:1¹
• Attack and Release: separate knobs that Delicious Audio says "allow for precise control over the dynamics"³
• Threshold: sets where compression kicks in⁸
• Type toggle: FET / OTA / OPTO⁵

The Blend knob is the parallel-compression control. Delicious Audio explains that "the always useful Blend knob lets you reintroduce some of the clean signal to achieve what's commonly referred to as 'parallel compression'"³. Keeping some uncompressed signal in the mix preserves pick attack and transient detail while the compressed side evens out sustain and level, which is why the technique is a studio standard.

Power: 9V in, 18V inside

The Phi V2 runs from a standard 9V DC power supply. Inside, a switch selects between 9V and 18V operation, with the higher voltage produced by an internal voltage multiplier, so no special 18V supply is needed¹. Crazy Tube Circuits' guidance is direct: "Use the 18V setting for increased headroom and enhanced compression characteristics"¹.

From the original Phi to the V2

The Phi V2 is a revision of the original Golden Ratio Phi, which Crazy Tube Circuits announced in August 2016. That first pedal combined two studio-grade compressors, optical and FET, in a single stompbox¹⁰¹¹, and its internal circuitry boosted a 9V power input up to 25V for additional headroom¹¹.

The V2, released October 8, 2021, made two big changes: it added a third circuit, OTA, for a total of three selectable modes, and it shrank the pedal into a compact case⁸³. MusicRadar's Jonathan Horsley described the update as adding "a trio of all-analogue compression circuits to the mix"⁴.

At launch the V2 was priced at €229⁴⁸, with Guitar World listing it at $249⁴⁸¹. Guitar Pedal X's Stefan Karlsson, reviewing it in October 2026, still listed it at €229 / $249 and called it "a fantastic 3-in-1 Compressor with 3 different circuits onboard"⁵.

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