The Golden Ratio Phi V2 is a multi-mode compressor pedal from Greek maker Crazy Tube Circuits, released in October 2021 as an update to the company's flagship compressor, the Golden Ratio Phi. Where the original carried two compressor circuits, the V2 puts three separate, all-analog circuits in one compact pedal, selected at a toggle switch: FET, OTA and optical12.
Each circuit is totally independent and has its own voice, with different compression characteristics and different ranges and responses from the controls2. The pedal covers a wide compression ratio range of 1:1 to 20:12, and its Blend knob allows parallel compression, mixing the compressed signal back with the clean, uncompressed one3.
Three compressor circuits in one pedal
The three modes are the heart of the pedal, and each suits a different job:
- FET uses a FET transistor for gain reduction. It adds distinctive color to the signal and can be extremely fast in its attack and release response, though it can add some unwanted saturation3. Gearnews describes it as adding "a fairly distinctive colour to your guitar signal" and possibly some "nice musical distortion"5.
- OTA is a very common technology in guitar compressors. It squeezes the signal more heavily, and with its feed-forward detector circuit it is ideal for catching and limiting fast transients, with a punchy, direct sound. Delicious Audio calls it "perfect for a funky rhythm guitar"3; Guitar World notes the circuit "takes inspiration from mainstream guitar compressor technology"6.
- OPTO is an optical compressor based on a hand-selected photocell combined with a feedback detector circuit. Like some classic studio units, it offers a musical but slower attack and release and sounds natural even at extreme settings35.
MusicRadar's Jonathan Horsley summed up the spread: the OTA "is able to put a serious squeeze on your sound for taming fast transients and limiting," while the optical side gives the smoother, studio-style response4.
The controls
The control panel carries six knobs plus the mode toggle5:
| Control | What it does |
|---|---|
| Volume | Sets the output level6 |
| Blend | Mixes the clean signal back in for parallel compression3 |
| Ratio | Compression ratio from 1:1 (no compression) to 20:1, where peaks above the Threshold level get squashed by 20 times3 |
| Threshold | Sets the level at which compression kicks in5 |
| Attack | Response speed; 1 ms to 30 ms range on the FET and OTA circuits8 |
| Release | Recovery time; 50 ms to 4 s range on the FET and OTA circuits8 |
| Mode toggle | Selects FET, OTA or OPTO circuit1 |
The separate Attack and Release knobs allow precise control over the dynamics3. Delicious Audio's take on the parallel compression technique: "With the parallel compression technique of blending the compressed signal with the original, uncompressed signal, you will experience clarity and precision only found in studio recordings"3.
MusicRadar also reports that the V2 has a low noise floor4.
Power: 9V or 18V from a standard supply
An internal switch selects between 9V and 18V DC operation, and the pedal runs from a standard 9V DC power supply in either position, using an internal voltage multiplier to reach 18V1. The maker recommends the 18V setting for increased headroom and enhanced compression characteristics1.
The 9V/18V selection is an internal switch, so changing it means opening the case. There is no battery option mentioned; the pedal is powered from a 9V DC supply1.
Where it came from
The original Golden Ratio Phi was announced in August 2016 as a stompbox combining two studio-grade compressors, optical and FET, priced at €250 and shipping at the end of August 2016910. MusicRadar noted at the time that its internal circuitry boosted a 9V power input up to 25V for additional headroom, and that it offered parallel compression via a blend knob9.
The V2 arrived in October 2021, shrinking the design into a compact case and adding a third compression mode, the OTA circuit, for a total of three34. It launched at €22945, with Guitar World listing it at $249457.
What reviewers said
Pedal of the Day reviewed the V2 in November 2021 and noted that "the three modes present in the φ (Phi) Golden Ratio v2 each have their own compressed voice"8. Guitar Pedal X's Stefan Karlsson, writing in October 2026, called it "a fantastic 3-in-1 Compressor with 3 different circuits onboard" and "super smart," while noting he would have liked a tone control overall7.
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Questions
What is the difference between the FET, OTA and Opto modes on the Phi V2?
Each mode is a separate analog compressor circuit. FET uses a transistor for gain reduction, adds distinctive color and can be extremely fast in its attack and release response. OTA squeezes the signal more heavily and is ideal for catching fast transients and limiting. Opto is based on a photocell with a feedback detector circuit, giving a slower, more musical and natural-sounding attack and release.
Does the Golden Ratio Phi V2 have a blend knob for parallel compression?
Yes. The Blend knob lets you reintroduce some of the clean, uncompressed signal alongside the compressed signal, a technique commonly referred to as parallel compression. Delicious Audio describes the result as a clarity and precision only found in studio recordings.
How do you switch the Phi V2 to 18V?
An internal switch selects between 9V and 18V DC operation, and the pedal still runs from a standard 9V DC power supply thanks to an internal voltage multiplier. You open the case and move the switch; the maker recommends the 18V setting for increased headroom and enhanced compression characteristics.
Is the Crazy Tube Circuits Phi V2 analog?
Yes. The Phi V2 is an all-analog design, and each of its three compressor circuits, FET, OTA and optical, is totally independent with its own voice, compression characteristics and control ranges.
What changed from the original Golden Ratio to the V2?
The original Golden Ratio Phi, released in 2016, carried two compressor circuits, optical and FET. The V2, released in October 2021, adds a third OTA circuit for a total of three selectable modes and shrinks the pedal into a more compact case.
Sources (10)
- Phi V2 - Crazy Tube Circuits, Crazy Tube Circuits
- Golden Ratio Phi v2 by Crazy Tube Circuits, RockBoard PedalPedia, 2026
- Crazy Tube Circuit Golden Ratio Phi V2 Multi-Mode Compressor, Delicious Audio, 2022-01-03
- Crazy Tubes Circuits upgrades its Golden Ratio compressor and packs three separate circuits in one pedal, MusicRadar, 2021-10-08
- New from Crazy Tube Circuits: Golden Ratio φ Phi V2 multi-compression pedal, gearnews.com, 2021-10-08
- Crazy Tube Circuits introduces new-and-improved, ultra-versatile Golden Ratio compressor pedal, Guitar World, 2021-10-11
- Guitar Pedal X, Guitar Pedal X
- Crazy Tube Circuits φ (Phi) Golden Ratio Compressor, Pedal of the Day, 2021-11-20
- Crazy Tube Circuits combines optical and FET compressors with Golden Ratio (Phi) pedal, MusicRadar, 2016-08-08
- Crazy Tube Circuits Releases the Golden Ratio Phi, Guitar Interactive Magazine, 2016-08-01
