Thermionic Culture The Phoenix SB

Vari-Mu Tube Stereo Compressor

• Vari-Mu-type dual-channel stereo compressor with all-tube circuitry
• No integrated circuits in the signal path
• From transparent, natural compression to extreme punch and tube saturation
• Continuous controls for gain, attack, release, threshold, and output on each channel
• Stereo link for working on groups and full mixes
• Side-chain filter with cut-off frequencies at 75 Hz and 150 Hz
• Standby mode that cuts tube current in half to extend tube life
• Front-panel trims for meter calibration

The Thermionic Culture The Phoenix SB is a vari-mu-type tube stereo compressor, built by the British brand with an all-tube design and no integrated circuits. This SB version retains the features of the previous Phoenix Side Chain—including the dedicated side-chain filter—and adds a Standby function and trims for adjusting the meters. It can deliver gentle, natural compression or, at higher ratios, a decisive punch and the warmth of tube saturation: a go-to choice for vocals, instruments, and especially the mix bus.

All-tube vari-mu compression

In the vari-mu circuit, the gain of the tubes varies in response to the signal, and the compression ratio increases progressively as the level rises. The result is smooth, musical compression that holds the material together without flattening it. The signal path is entirely tube-based and free of integrated circuits, with an extremely linear frequency response and excellent phase coherence.

From Transparency to Punch

At light settings, the Phoenix SB operates transparently, adding cohesion and a touch of warmth. By increasing the gain and the amount of compression, however, you’ll achieve pronounced punch and tube saturation that adds character to drums, bass, and vocals. Gain, attack, release, threshold, and output are continuous controls, allowing you to precisely adjust the behavior for each source.

Tube Compressor for the Stereo Bus and Mix

The two channels can operate in stereo-link mode to process groups or entire mixes while maintaining a stable stereo image. When inserted as a compressor on a mix bus in a DAW, the Phoenix SB delivers all the warmth of a true tube processor—a feature that makes it particularly popular in hybrid studios.

75 Hz and 150 Hz side-chain filter

The side-chain filter, with selectable cutoffs at 75 Hz and 150 Hz, reduces the influence of low frequencies on detection. Kick and bass no longer drag the entire mix into compression, and you can work on the bus with more aggressive settings while preserving the body of the low frequencies.

Standby Mode and Meter Trim

The Standby function reduces the current flowing through the tubes by 50%, preserving the tubes and capacitors during breaks without having to turn off the unit and wait for it to warm up again. The Phoenix SB thus remains ready for use throughout the session, with longer component life.

Quick Meter Calibration

Two trims on the front panel allow you to adjust the meters quickly and precisely, so you can check and align the readings of the two channels without opening the unit.

Technical Specifications

• Brand: Thermionic Culture
• Model: The Phoenix SB
• Type: dual-channel vari-mu tube stereo compressor
• Circuitry: All-tube, no integrated circuits
• Controls: gain, attack, release, threshold, output (continuously variable)
• Modes: dual mono or stereo link
• Side-chain filter: 75 Hz and 150 Hz
• Standby: 50% reduction in tube current
• Meter: adjustment trim on the front panel
• Maximum output level: +19 dB into 600 ohms, +24 dB into 10 kOhms
• Maximum gain: 30 dB
• Total harmonic distortion: less than 0.09% at 1 kHz (without compression), 0.11% at 100 Hz
• Noise: 95 dB below maximum output level
• Frequency response: 0 / -1 dB from 12 Hz to 60 kHz
• Attack time: 0.004 s to 0.12 s
• Release time: 0.06 s to 2.2 s
• Input impedance: 15 kOhm
• Output impedance: 600 ohms