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Thermionic Culture Phoenix Mastering Plus

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Dual Mono/Stereo Mastering Tube Compressor. A modern classic!

-All valve signal path and side chain, point to point hand wired in England.

-Subtle control with 'soft knee' compression more compression effects when pushed hard.

-Stereo link for mix buss compression.

-Side chain filters to enable compression of all frequencies except bass.

-Flat frequency response over full audio range and beyond.

-Very low phase shift and harmonic distortion (unless pushed hard).

-Push-pull design gives a natural warm sound with high output level.

-Output trim controls for fine adjustment or lower level operation.

-Balanced ins and outs with custom made Sowter transformers.

-Bypass switch on each channel removes all electronics.




-Elma switches for gain and threshold controls.

-Alpha switches for attack and release controls.

-All Mullard and Siemens NOS valves.

-Easy recall- ability.

-Zero adjustment on front.


This is the latest development in the evolution of the classic Phoenix compressor, first introduced in 1998. After requests from mastering engineers the Master Phoenix was introduced in October 2006. This was more recall-able with indented pots and slightly different power supply and metering circuit, in which trimming the meter alters the current through the compression valve so compensating for valve ageing.

The compression curve of the mastering Phoenix is slightly gentler than that of the standard one, but it does have a more "positive" effect. This earlier version has 6dB lower gain compared to the standard Phoenix.

The Master Phoenix is in use in many studios and mastering suites around the world, and we do know that one of its users, Ray Staff of AIR London Studios won the MPG award for Best Mastering Engineer in 2009.

The new Mastering Plus is a much upgraded version employing precision Elma switches for the Gain and Threshold and Alpha switches for Attack and Release. Omeg indented pots are used for the Output Level for fine control.

Side Chain Bass Cut switches, which have become an essential mastering tool have been retained. In stereo mastering, with the link switch in, there are effectively 5 frequency options as the compressor side chain will work at the average of the switch positions.

A Standby switch is introduced to prolong valve and component life and this has had an unexpected effect, see. *

Mullard and Siemens NOS valves are used exclusively for lower noise and long life stability.

The Gain is now identical to that of the standard Phoenix so that extreme compression effects are possible .

Easy adjustment of Meter Zeros, especially important in stereo mastering, is now enabled by front panel access to the trim controls, situated between the 2 meters.


*some users have found that analogue tape type distortion is created when the unit is operated with Standby on.This was unintentional but some people may find it interesting.

Max. o/p level (MOL):

+19dB into 600Ω

+24dB into 10kΩ

Max gain: 36dB
THD (at no compression): better than 0.06 % @ 100Hz & 1kHz
Noise, IEC weighted: better than 100dB below MOL
Input impedance: 15kΩ
Frequency response: less  than 1dB variation over range of 12Hz to 56kHz
Attack time: 0.004s to 0.12s
Release time: 0.04s to 2.4s
Output impedance: 600Ω


Distortion will increase with compression, typically 0.2% & 0.25% at 1kHz & 100Hz with 8dB compression.

Attack and release controls are somewhat interdependent, for instance a change of attack setting may affect the release time slightly. Therefore, no times are given on the front panel.



-Input/Compression: PCC85 (equiv. 9AQ8)

-Output: ECC81 (equiv. 12AT7, CV4024)

-Side chain detector: EB91 (equiv. 6AL5, CV4025).




You buy a Thermionic Culture Phoenix for what it does to the sound, plain and simple: this is a compressor in the classic vintage mould, with lots of character and sonic warming, and the almost uncanny ability to help mixes gel in a smooth and flattering way.

Unlike some variable-mu designs I've heard, the Phoenix always sounds expensive, cultured and in control, never unnatural or artificial in any way. It always enhances the sound in a musically satisfying way, and controls transients and programme dynamics sympathetically and with effortless ease.

Sound On Sound

Read the complete review here



On delicate source material the Phoenix is superb, providing a lovely cohesiveness in an open, transparent manner. On complex, bass-heavy mixes its versatile features enable you to add the final touch that makes the difference between an OK-sounding mix and a radio-ready recording.

Music Tech

Read the complete review here


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