Review: Thermionic Culture Phoenix

The Phoenix is built to offer the best in hand-made vintage-style compression. And not to be consumed by flames after its useful life.


18 October 2006

Review: Adam McElnea

Thermionic Culture is a small UK-based boutique audio company that specialises in professional hand-built valve audio gear. Founded by the valve guru himself, Mr Vic Keary, whose extensive studio experience dates way back to the ’50s, Thermionic Culture evolved from good ol’ British know-how, with a sound that ‘glows’.


Do we really need another valve compressor, and quite an expensive one at that? Well, in short, if it looks and sounds as good as this one… then, yes, we do. Housed in a substantial 3U high chassis, the Phoenix’s appearance is striking. My immediate impression was that if this unit sounds as good as it looks, it will be hard for the Phoenix and me to ever part company.

The Phoenix is a dual-mono (stereo linkable) delta-mu valve compressor that’s ‘loosely’ based on the vintage Altec 436 design, with considerable updates for improved noise and distortion specs. A key ingredient in Thermionic Culture’s sound is its aversion to anything solid-state. In fact, the only place where you’ll find any solid-state circuitry in the Phoenix is in its power supply; the audio signal path is completely valve. Unlike opto-, VCA- or FET-style compressors, delta-mu or vari-mu designs utilise a tube for the gain control mechanism and inherently offer extremely smooth soft-knee operation. The formidable Fairchild 670 and compressors made by Manley Labs and Pendulum Audio are among the few designs that utilise a vari-mu approach.


There’s no ratio control on The Phoenix as such; the harder you drive the unit the higher the ratio. Ranging from 1.2:1 to 5.1 at 15dB of compression, the Phoenix offers both subtle and heavier processing. Unlike other ‘mu’ designs, however, this unit doesn’t offer a limit function.

The beautifully finished gloss black front panel sports continuously variable individual channel controls for Gain, Attack, Release, Threshold and Output. A pair of huge (non-backlit) white mechanical VU meters set the unit apart from anything else you might have in your rack. These VUs are quickly becoming Thermionic Culture’s calling card. Lastly, a Link control is provided for stereo operation, as are toggle bypass switches, and a smart-looking bright green power light. Quirky, arbitrary markings from 1 to 11 are used to gauge time and level constants – not particularly informative, I’d prefer some form of conventional scale markings. The manual specifies the attack times as ranging from 4ms to 120ms, while release times vary from 60ms to 2.2 seconds.

The unit definitely oozes hand-crafted individuality. No corners have been cut, with point-to-point hand soldering and wiring, and no PCBs in sight. The unit is well ventilated and most major components are clearly visible through the upper casing. Notably, these comprise a pair of massive Sowter transformers, an oversized power supply and three valves per channel. The exotic valve selection consists of one PCC85, one 12AT7 and one 6AL5 per channel, however, earlier units used a 6BQ7A in lieu of the PCC85s.

On the downside, however, the unit doesn’t include a sidechain facility or a high-pass filter option, which, I’ve no doubt, will confound quite a few people reading this. The manual does specify a workaround option for performing ducking or frequency-conscious compression, however, it involves using one channel in conjunction with the other and therefore restricts the unit to single channel (mono) operation only.

Overall, the design has a great retro feel and the attention to detail and ‘boutique’ individuality is something that’s rarely seen in today’s market.


With all connections made and the unit powered up it was time to put the Phoenix through its paces. First up, I should mention that if you’re looking for a new compressor to add so-called ‘warmth’ to your mixes as well as your studio, look no further, as the Phoenix dissipates heat like a gas radiator!

As soon I passed audio through the Phoenix I immediately knew I was listening to something extra special. Mu-style compressors are well known for their ‘glue’ and smooth operation, and this unit is definitely no exception. I started testing the unit on stereo sources, from minimal acoustic sessions through to R’n’B, dance and rock… and many styles in between. The results were nothing short of spectacular. The Phoenix really does sound as good as it looks. ‘Glue’, ‘cream’, ‘vibe’, ‘mojo’, ‘expensive’ were all words that quickly came to mind. This is one of those devices that just makes everything sound better, and it seems to do it better than most of those others that seem to make everything sound better… if that makes sense! The secret to getting a great sound out of a Mu compressor is the ‘Drive’ facility. That is, the harder you drive the input the larger the passed signal becomes thanks to the addition of valve harmonics. However, if size and depth are not what you’re after but transparency is, then back off the drive and turn up the output instead and, voila, you’ve got pristine compression at the twist of a knob.

When compared to my long-time companion, the Vari-Mu, I found the Phoenix just took that wonderful creamy Manley sound to the next level. It sounded more ‘natural’ with an increased level of realism and immediacy, while the Manley always sounded slightly ‘artifical’ and ‘tubey’. The Phoenix adds an expensive richness to all sources that extends from its deep bottom-end right up to its subtly smooth silky tops. For taming transients, the Phoenix performed flawlessly. With its Fairchild-esque smooth attack and release settings it was easy to round-off material or add a bit of punch and excitement if needs be.

As a dual-mono compressor for tracking, the Phoenix performed at the highest level. On vocal stems the Phoenix added an expensive forwardness that I had rarely experienced with any other compressor. Definitely larger and more dense sounding, the vox remained detailed with superb low/mid purity and excellent articulation. On guitar and bass the unit added expensive character as well as resolved detail, while retaining a true sense of realism and speed. Driving the unit a little harder resulted in the rounding or smoothing of resonant harsh frequencies with minimal artifacts. Turning to the drums had the Phoenix in its element. Whether you’re looking for a rounder, thick sound or a tight punchy vibe the Phoenix had all bases covered. The unit’s tight deep bottom-end works magic on all drums, while its versatile controls provide a healthy variety of sound sculpting possibilities. Percussion is smooth and natural sounding.

The Phoenix is a very musical-sounding unit and just what the doctor ordered if you’re dealing with digital sterility or ‘second division’ plug-ins. In fact, just running signal through this box imparts its own lush sonic signature and breathes new life into two-dimensional material.


The Phoenix is remarkably quiet for an all-valve unit. Boasting noise figures as low as 95dB below MOL (IEC rated) and an effectively flat frequency response over the entire audio range and beyond, the Phoenix excels where others leave off. This is a truly stellar-sounding box that gives a gentle mystical glow to anything that passes through it.

Aside from its ‘pro price’ and the fact it doesn’t have sidechain or filter options, the Phoenix has plenty to love, including its simplicity, hand made personality, funky retro looks and most importantly, ‘that sound’. Suited equally well to tracking and mix-bus applications, the Phoenix valve compressor, like its flaming namesake, is destined for immortality among the vari-mu greats. Yes, it’s out of the price range of most, but I’d suggest the Phoenix still represents value for money – best components, hand crafted… it hardly gets more ‘boutique’ than the Phoenix. Highly recommended!


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