Crazy Tube Circuits Golden Ratio Phi

The Golden Ratio Phi is a compressor pedal from Crazy Tube Circuits, a builder MusicRadar called "Greece's premier pedal builder"¹. Released in August 2016, the original Phi put two studio-grade compression circuits, optical and FET, in a single stompbox, an approach MusicRadar described as "a compressor that crams optical and FET circuits into one stompbox"¹. Guitar Interactive Magazine reported that it would "fatten up your tone even with no compression added"².

In October 2021 the company revised the pedal as the Phi V2, shrinking it into a compact case and adding a third compression circuit, OTA, for a total of three selectable all-analog compressors³. The V2 also brings a Blend knob for parallel compression, the studio technique of mixing the compressed signal with the untouched original. Delicious Audio reports that with this blend "you will experience clarity and precision only found in studio recordings"⁴.

What the Golden Ratio does: parallel compression in one pedal

A compressor evens out a player's dynamics by turning down the loudest peaks, which raises sustain and keeps a part sitting consistently in a mix. The Golden Ratio's distinguishing idea is that it offers several different compressor "voices" in one box rather than one fixed circuit, with FET, OTA and Optical circuits onboard, and, in the V2, a Blend knob that lets the player reintroduce some of the clean signal for what's commonly referred to as parallel compression⁹⁴.

That blend is what players call parallel compression. 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'"⁴. MusicRadar notes the V2 "uses parallel compression for studio-quality sounds" and "has a low noise floor"⁷. The maker says the Phi V2 offers "superb low-noise floor performance and full frequency response making it ideal for guitar, bass and virtually every instrument" on stage or in the studio¹⁰.

The controls

The V2 carries six knobs and a mode toggle. Gearnews lists the control set as "Volume, Blend, Ratio, Release, Attack, and Threshold"⁶, and Pedal of the Day explains what each does⁸:

Delicious Audio notes that "separate knobs for Attack and Release allow for precise control over the dynamics"⁴. The Ratio knob applies compression from 1:1 (no compression) to 20:1, where the peaks above the Threshold level get squashed by 20 times¹. In OPTO mode the ratio range is 1.5:1 to 15:1, with attack times of 1 ms to 30 ms in the FET and OTA circuits and release times of 80 ms to 4 s in the OPTO circuit⁸.

There is no tone control. A Guitar Pedal X reviewer called the pedal "super smart!" and said it delivers everything essential, though he would have liked a tone control overall⁹.

FET, OTA and Opto: the three circuits in the V2

Each of the V2's three circuits is a fully independent analog design with its own character, selected at a toggle switch⁴. RockBoard's PedalPedia describes them as "each all-analog circuit is totally independent and has its own voice with different compression characteristics"¹¹.

• FET: A feed-back detector and control circuit that relies on a FET transistor for gain reduction⁸. MusicRadar says it "uses a FET transistor for taming spikes in your gain and tightening things up" and may add tube amp-style warmth and a little distortion⁷. Guitar World describes it as suitable for "super-fast response and subtle musical distortion"³.
• OTA: A feed-forward detector circuit that Pedal of the Day says can "squeeze" things harder; Guitar World calls it "a circuit that takes inspiration from mainstream guitar compressor technology"³. GuitarPlayer's reviewer noted that "OTA recalled the circuit type used in many pedal compressors"⁵. Pedal of the Day calls it "the most controllable circuit with punchy and direct sound," ideal for catching fast transients and limiting⁸.
• OPTO: Built around a hand-selected photocell combined with a feed-back detector circuit⁸. Delicious Audio says it offers "smooth attack and release characteristics" and can be set very neutral⁴; Pedal of the Day found it delivers "very musical and organic compression even on extreme settings"⁸.

From the original Phi to the V2

The original Golden Ratio Phi launched in August 2016 at EUR 250, combining its two circuits in one box¹. Guitar Interactive described the optical side as offering "very gentle and musical compression which is generally not found in typical solid state or tube designs," and the FET side as "a highly tweakable compressor with separate controls for attack and release" that "can be tweaked to sound very clean or colored," coloring the tone "in the most musical way" at extreme settings, like studio classic FET compressors². That original ran its internal circuitry at 25V DC of clean headroom from a standard 9V supply².

The V2, announced in October 2021, "updates the Greek company's flagship compressor by shrinking it into a compact case and adding an extra compression mode"⁴. Guitar World reported it was "available now for $249"³; MusicRadar and Gearnews both listed it at EUR 229⁷⁶. The V2 runs at 9V or 18V, selected by an internal switch that works from a standard 9V DC supply via an internal voltage multiplier⁸. Delicious Audio advises players to "use the 18V setting for increased headroom and enhanced compression characteristics"⁴. The maker's store also lists a B-Stock Phi V2 offered at a reduced price¹².

What reviewers said

Published reviewers were positive about both versions. GuitarPlayer's review of the Golden Ratio called it "extremely versatile" overall⁵. Pedal of the Day, reviewing the V2, wrote:

Guitar Pedal X's Stefan Karlsson called the V2 "a fantastic 3-in-1 Compressor with 3 different circuits onboard" and "super smart!"⁹.

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