~Sebatrons~  newest offering, THORAX valve channel strip

THORAX valve channel strip, from Sebatron is based upon their successful vmp (valve mic pre) series mic pre. Already in wide use in Australia, Sebatrons vmp’s are quickly gaining a solid reputation internationally as affordable, reliable and most importantly, as sounding really good. High quality, Class A, all discreet and transformer balanced, Sebatrons have found their way into home, project and pro studios all over the planet.

A mic pre, equalizer and electro optical compressor “all in one” package, THORAX’s transformer balanced tube mic pre is an expansion of the vmp series. The EQ is a two band switchable passive type with a “colour” selector and an electro optically driven tube compressor employs a Sebatron custom designed gain reduction circuit that providing fast, tight control over signal dynamics without audible side effects.

THORAX'S PRE and EQ sections

 















The chassis, constructed from solid steel, is powder coated black with white silk screen legends. On the front panel there’s a latching XLR mic level input and ¼” direct instrument / line level input, followed by a two way pad, switchable to -10dB or -20dB, switches for phase and phantom power and pre amp output level control. A “colour” rotary switch controls tube drive, offering five settings ranging from -12dB, to +12 in 6dB increments and a final 12dB boost to +24dB, followed by the EQ in / out switch. The equalizer is a passive high and low frequency shelving type, consisting of six “Air” presets labeled cut, classic, flat, open, air 1, air 2 and “Deep” presets labeled gaunt, cut, flat, warm, deep 1 and deep 2.

THORAX'S Compressor Section

The compressor features fully variable controls for threshold, ratio, attack and release. A switch labeled “A/R factor” extends the range of the attack and release controls and a “Drive” switch changes the gain and tube color of the compressors make up gain stage. Finally, there is a green backlit VU meter, which may be switched to monitor the mic preamp, main output or the compressor gain reduction, followed by a low profile rocker type power switch.

Located on the rear panel is the fuse holder and mains voltage selector switch which selects 110-120V or 220-240V operation and a standard IEC mains receptacle. There is a second XLR for microphone input to accommodate those who don’t care for mic cables running into the front of their racks. The balanced mic pre output is provided as both a XLR and a ¼” trs jack and bypasses the compressor stage. Input to the compressor is provided on a standard unbalanced ¼” trs send / receive socket and acts as an insert point between the mic pre and compressor, allowing the mic pre / EQ section and compressor to be used as separates. The send may be used as an unbalanced output for the mic pre while the return serves as input for the compressor. A XLR and ¼” balanced trs jack serve as the compressor output. There is a ¼” trs sidechain jack, accessing the compressors detector for ducking, de essing and frequency dependent compression applications.

THORAX excelled with bass instruments. Selecting “Deep 1”, both Korean Dano Longhorn and a ’54 MIJ Fender reissue Precision bass displayed nice detail and depth. The EQ, despite its preset nature provides settings that are just right to control highs, mids and lows. It’s not hard to grasp the approach followed especially when you consider Sebatrons old school fanaticism in regards to phase anomalies caused by EQ’s. Their answer is to use switchable passive eq presets. THORAX’s presets in use, while limited, are recallable, well thought out, useful and a good compromise between affordable, effective and high end tweaky.


I have been a user of the vmp mic pre for some time. With mics like 421’s, SM7a’s or SM 57 / 58’s, they shine. Engaging “AIR 1” on THORAX, the vmp pre adds attack on percussive sounds or presence and sheen for vocals. Nevertheless where I’ve found the vmp really shines is with my U87ai, making this newer Neumann sound fabulous. With the U87ai aimed at the 12th fret and about four inches off a Martin D 28 with the Hi EQ set to “Open”, the sound is full, robust, with just the right amount of “jangle”. The THORAX, with its preamps added gain, can now accommodate low level sources.

In the “Cool” setting, the compressor effectively controls dynamics while remaining unobtrusive and transparent, adding a slight thickness to the signal much likes a LA2a or EL OP type. Switching to “Warm”, the harmonics begin to increase, bringing up a squishy “silk” that is often sought especially for that classic “Nashville” acoustic guitar sound. “Hot”, brings up a radically “distressed” signature, reminiscent of modern designs that attempt to replicate vintage tube or FET sounds by boosting low end content and distortion. I found the compressor section of THORAX very flexible. The compressor sections of two THORAX’s may be linked to provide true stereo operation or for mastering applications.

Each of the THORAX’S sections could stand on their own. The expanded vmp mic pre is stellar, the EQ, while limited by its preset nature, can be very effective if applied appropriately. The compressor is a chameleon, capable of delivering many different sonic signatures, depending on the settings chosen via the “A/R Factor” and “Drive” controls. In terms of flexibility, THORAX is well suited to all types of “Pop” production, from Urban to Country. The fit, finish and build quality of the review unit was more than excellent, it was perfect. Moderate pricing allows the studio owner on a budget to now consider a pair for mastering and stereo applications when they may have been thinking about being able to afford only a single high quality channel strip for tracking vocals and individual instruments. Sebatron has come up with a winner with the THORAX, combining a world class tube mic pre, an easy to use but effective passive equalizer and a versatile compressor in an affordable all in one package.

THORAX lists for $2000 U.S.D.

Find ~ Sebatron ~ on the Web at: www.sebatron.com


©Kurt Foster 2005
(p) Kurt Foster 2005

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