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Tonelux V8 Roadster

Modular Outboard Processors By Hugh Robjohns
Published January 2009

Modular processing systems are growing in popularity. This contender from American makers Tonelux puts the emphasis firmly on quality.

Three XLR connectors for each module are fixed to the rear panel, and above these there's a slot to allow access to another connector that's found on some of the modules themselves. The 25‑pin D‑sub sockets allow for easier multi-channel connection in the studio.Three XLR connectors for each module are fixed to the rear panel, and above these there's a slot to allow access to another connector that's found on some of the modules themselves. The 25‑pin D‑sub sockets allow for easier multi-channel connection in the studio.

Modular audio processing racks don't suit everyone's requirements, but it is certainly a very flexible way to build up some great quality and varied outboard in easy incremental stages. The Tonelux modules reviewed here, designed by Paul Wolff, may appear superficially similar to the widely supported API 'Lunch Box' module format, but they aren't actually a compatible variant: you can only use them in Tonelux's own 16‑slot V‑rack chassis, or the smaller, eight‑slot V8 Roadster case. However, this bespoke system has the advantage that any module can be placed anywhere you like in either rack, and the range currently comprises a nice mic pre, a flexible equaliser, a stunning compressor, various stereo and surround mixing and aux modules, master output modules, a monitoring section, and even fader panels. As a result, you can build anything from a basic channel strip, multi‑channel mic preamp or summing amp through to a fully functional and very comprehensive surround‑capable console. What's more, at the time of writing, the Tonelux web site had an announcement that Little Labs' IBP and SPL's Transient Designer are now being made for this format.

For this review, I was supplied with two MP1 mic preamp modules, an EQ4P equaliser and a TXC compressor, all of which came pre‑installed in the compact V8 Roadster chassis. Sadly, there was no manual supplied with any of this — Tonelux apparently don't 'do' manuals — and there are only minimal and patchy details on line, so a degree of guesswork and experimentation has been required on my part.

Module Overview

Starting with the V8 chassis, this is very solidly built, with a convenient carrying handle on the top, and rubber feet on the working and carrying bases. Unlike the larger V‑rack chassis (which uses an external power unit), the V8 rack contains its own internal universal mains power supply, and a recessed multi-pole socket can provide DC power to feed a separate V‑rack if required (the appropriate cable is supplied with the V8). The mains power inlet is via an IEC socket with an integral switch and fuse, and it accepts 95‑250VAC.

The rear chassis panel carries three fixed XLR connectors for each module slot — two inputs and an output — and a recessed space above allows access to a fourth connector on the module itself, although not all modules use this facility. There are also six 25‑pin D‑sub sockets, mostly arranged along the bottom of the back panel, which provide multi-channel access to the stereo‑ and surround‑mix buses, insert sends, PFL/Solo and switching logic buses, the module balanced inputs, balanced insert return/side‑chain inputs and balanced outputs.

MP1 Preamp

The MP1 preamp has recently been upgraded to the MP1A version, and there is also a remote‑controllable version, but the review system was fitted with the original MP1. This is a very neat little preamp, with a transformer input and discrete gain circuits plus the Tonelux TX260 discrete op‑amp module driving the output transformer.

The front panel carries an input gain knob, five illuminated push‑buttons, a simple tilt equaliser (I'll come back to that...) and a 'combi' jack/XLR socket that accepts either a microphone input or provides a high‑impedance DI guitar input. A second XLR mic input is provided on the rear panel, wired in parallel with both the front-panel socket and the rack's input XLR and D‑sub sockets. The quarter‑inch DI input in the 'combi' socket is unbalanced, and presents an input impedance of 250kΩ. The output is presented on the Direct Out XLR and D‑sub sockets on the rack, as well as on the internal rack mix buses.

The input gain knob provides 35dB of control range, although extra gain can be specified as a special option. The only difference between the new MP1A module and the one reviewed here is that the new version has a dual‑concentric gain knob: the larger outer ring sets the input gain, while the upper knob serves as an output level fader — a useful additional facility, but not essential. Distortion is a commendable 0.02 percent at 800Hz, but rises to 10 times that at 20Hz, thanks to the transformers. The output clips at a very generous +29dBu.

The push buttons provide polarity reversal and a 20dB attenuator, switch on the 48V phantom power, select the DI input instead of the mic input, and provide PFL monitoring (via the rack's PFL output bus connector, or a suitable master module if installed). Running down the side of these push buttons is an eight-step LED VU meter calibrated from ‑20 to +14dBu in 4dB increments (zero equates to +4dBu), although the top LED is actually a fast‑acting peak indicator.

The EQ Tilt control at the top of the strip has its own hardware bypass on/off switch, and provides up to 6dB of treble boost and bass cut (or vice versa) on the output signal. This equaliser stage is effectively a pair of cross‑coupled shelf equalisers, and it is designed to have little effect on the critical 400‑1500Hz mid‑range region. Although this may seem a very simple idea, it is surprisingly useful and usable — and I was often able to shape a source using it rather than a traditional EQ.

Obviously, the 'insert return/side‑chain' input socket on the rack panel for this module is superfluous, so Tonleux have reallocated it to serve as a high‑impedance mic‑level split for those live recording situations where a proper mic splitter isn't available.

The use of transformers at both ends of the signal path gives this preamp a slightly rich and generous‑sounding bottom end, but it's not overdone, and the open and airy top end balances it very well. The overall effect is of that slightly larger‑than‑life character than is common to all the best preamps, and it certainly sounds very musical, clean, fast and competent.

EQ4P Equaliser

Tonelux V8 Roadster

The EQ4P equaliser module again features the TX260 discrete output stage and transformer, and all of the I/O interfacing is via the rack — there are no connectors on the module itself. The main rack input and output XLRs operate with nominal +4dBu signals, while the insert return/side‑chain input socket is padded down by a further 6dB to accommodate 'hot' signal levels from DAWs or professional D‑A converters.

This is a four‑band EQ, all four being bell filters with adjustable gain and frequency. The gain is set with the outer/lower silver knobs, while the frequency is tuned with the inner/upper black knobs. The top band can also be switched to a shelf response, while the other three can be configured to have a constant 1/3‑octave bandwidth. In normal use, the bandwidth of each filter stage varies depending on the gain setting — a scheme called 'proportional Q' or 'constant energy' equalisation. More gain provides a narrower bandwidth, so that small boosts or cuts are wide and gentle, while aggressive equalisation is narrow and precise. It's an arrangement used on a lot of classic equalisers, and works very well.

The four bands all have very generous overlaps. The lowest band can be tuned between 16Hz and 1kHz, while the lower mid covers 50Hz to 3kHz. The two upper bands both cover the same 500Hz to 21kHz range, but that's no hardship. An overall bypass button is provided, but there are no individual section bypasses — although the gain controls all have centre unity‑gain detents. When bypassed, the filter circuitry is omitted from the signal path, but the input buffers and output transformer are still in circuit, and provide a mildly rich character.

TXC Compressor

This compressor module is the latest addition to the Tonelux range, and it is a particularly interesting and versatile design, able to apply 'parallel compression' and over‑compression, and to select either feed‑forward or feedback topologies (or both at the same time!). Once again, the TX260 discrete gain stage is in evidence, along with the same output transformer as the other modules, supplemented with a TX240 discrete op‑gain circuit. The actual dynamic gain control appears to be performed by several of the ubiquitous THAT chips — there are separate sections for the feedback and feed-forward control paths.

The front panel is rather more complicated than on most compressors, and the small amount of real estate for labels makes it tricky to find your way around at first, but given the flexibility of this unit that's hardly surprising. And without a manual, finding your way around is a challenge — although the web site does have some useful information to ease the learning curve slightly, and to help you understand what the three dual‑concentric controls, a couple of single knobs and four illuminated push‑buttons all do.

Starting at the top, the first dual‑concentric knobs set the ratio (inner) and threshold (outer). The threshold control spans a useful ‑20 to +20dBu range with a centre detent at the zero level position. The first half of the ratio control's rotation provides the normal ratio progression from 1.5:1 up to 20:1, after which it goes into the over‑compression mode — although this is all a bit vague because the ratio markings don't necessarily tie in with what's actually happening. The actual ratios depend on the feedback/feed‑forward mode in use at the time. In practice, though, you adjust these controls according to what your ears are telling you, rather than your eyes, so this isn't as big an issue as it might seem at first. There's no manual make‑up gain control — that is taken care of automatically, so that as you increase the ratio or adjust the threshold, the output level stays the same and the sound gets more dense.

The next concentric-knob pair adjusts the attack and release time constants. The attack range is marked from 0.05 to 30, while the release control goes from 0.2 to 3 (I presume these figures are seconds and it certainly sounds that way, but there are no published specs to confirm that assumption). An illuminated push‑button is labelled 'Att x5', and this speeds up the attack time constants to super fast microsecond‑timescales. The release circuit is apparently a three‑stage design that applies a faster decay for loud HF signals than LF signals. It certainly sounds very transparent and natural in use.

The EQ4P four‑band EQ module features dual‑concentric knobs. It has been designed to give plenty of overlap between the bands, each of whose bandwidth (in normal use) varies according to the gain setting.The EQ4P four‑band EQ module features dual‑concentric knobs. It has been designed to give plenty of overlap between the bands, each of whose bandwidth (in normal use) varies according to the gain setting.The next dual‑concentric control determines the side‑chain type — feedback or feed‑forward on the inner knob — and the amount of external influence from the side chain or stereo Link signal, which is set as a percentage on the outer knob (from 50 to 100 percent). In feedback mode, the compression ratio barely exceeds 5:1 at the maximum setting, regardless of what the control knob says. The circuit design also means that very brief transient peaks tend to slip through regardless of the attack time setting — and this is quite common for this type of compressor topology, because of the way the feedback control signal works in a closed loop that can only react once the signal has passed. As a result, feedback topologies are usually relatively gentle, and most production compressors were feedback types up until the 1980s and 1990s. So in feedback mode the TXC tends to sound fairly 'vintage.'

The feed‑forward topology is far more aggressive and tends to be used more where absolute level control is required, such as in transmission‑chain devices. It only really became popular in studio compressors in the late 1980s and early 1990s. In this mode, the ratio control does exactly what it says on the panel label, from 1.5:1 up to 20:1, and then the over‑compression or 'reverse ratio' effect comes in. If you have a normal ratio such as, say, 10:1, the input has to rise 10dB above the threshold to make the output rise by 1dB. In the over‑compression mode the ratio is more like 10:‑2, so that if the input rises 10dB, the output actually falls by 2dB. In other words, as the signal exceeds the threshold its output level gets turned down even more — and the TXC provides reverse ratios up to about 10:‑8.

This is an odd but quite interesting effect, and there are suggestions on the web site as to how it can be used to increase the perceived dynamic range of a percussive signal that has already been compressed too heavily. If you set a slowish attack time to let the transient through, a reverse‑ratio setting will then lower the level of the following decay, thus increasing the overall dynamic range and undoing some of the effects of a previous compression or limiting process. It does work, too, although it is a little fiddly to do.

But you're not restricted to just feedback or feed‑forward topologies in the TXC. Both systems are working all the time, and you can blend their outputs together to create even more interesting tonal characters. In general, a blend of the two provides a softer knee through the transition region around the threshold level, but the stronger feed‑forward mode tends to dominate if the blend control is above about 30 percent.

The next control brings us back to the Tilt equaliser that I described for the mic preamp module, only this time it is placed in the compressor's side‑chain circuit so that the compressor's sensitivity to LF or HF signals can be reduced or increased. This is extremely useful if you are working with a very bass‑heavy track, for example, since a high level of bass would normally dominate the compressor's side-chain and usually result in pumping. If you adjust the tilt control so that the side‑chain favours the higher end more and the bass end less, the compressor can be persuaded to control the level of the signal based more on the mid and upper ranges, instead of just the bass, giving smoother results.

Running down the side of the tilt control is a gain‑reduction meter of six LEDs, showing up to 25dB of reduction, and the final, bottom knob determines the output‑signal blend of direct and compressed signals. This allows very easy creation of 'parallel compression' which is a very gentle and natural‑sounding form of compression that's used regularly in classical and mastering applications. It is very handy to have the option here, and it completes an extraordinarily comprehensive and capable compressor.

In Use

This is a very well-built and well-specified modular system, extremely versatile, with plenty of interesting and useful features and facilities. The rack itself is well designed: installing and removing modules is very straightforward and the I/O interfacing is well thought-out, permitting easy access to individual channels as well as neat multi‑channel cabling options in a permanent installation.

The mic preamp sounds very musical and has a solid bass end, coupled with a nice open, high‑end sheen and a slightly larger‑than‑life character. The Tilt control is a very useful addition which I used a lot to gently shape or control the spectrum in creative ways, often helping to compensate for less than ideal mic positioning or choice without having to resort to a full equaliser.

The EQ module, although rather fiddly to use because of the density of controls and proximity of other modules alongside, is capable of very subtle, gentle tonal‑shaping, as well as powerful corrective tweaking. The band overlaps ensure that every part of the spectrum can be accessed and tweaked without problems, and the progressive Q function is so much easier than having to adjust a separate bandwidth control (and takes up less panel space too).

The compressor module is the hardest to get to grips with, partly because of the dense array of controls and difficulty in reading the control labels, but also because it has some very unfamiliar functions. However, perseverance is certainly rewarded: this is a really interesting and creative compressor that can do pretty much anything you want. Very gentle, uplifting parallel compression is but a twist of a knob away. Normal compression can be configured for everything from slow and gentle levelling, through hard‑rock vocal dynamic control and absolute peak limiting, to some really weird and interesting effects, and on to possible dynamic-range restoration in some situations. It almost seems able to act as a time‑machine too, through the variable feedback/forward topology blend. Whichever way you look at it, this is an extremely impressive tool.

Overall, this Tonelux system is a serious kit of parts that is up there with the big boys — though it doesn't enjoy the universality of API's 'Lunchbox' system. Starting off with any modular system like this isn't cheap, but the fiscal benefits come as you add more modules, and the ability to mix and match modules to suit your own needs is a significant advantage over traditional outboard hardware. The Tonelux modules give the impression that cost isn't the limiting factor here — they're designed to be right, and to provide a really useful set of tools. I'd love to hear a console built out of these modules!


The obvious alternatives are the numerous 'Lunchbox'-style systems made by a variety of manufacturers and working to an interchangeable module format, and similar bespoke, closed systems, such as the SSL X‑rack and Audient Black Series.


  • Superb range of modules providing immense system flexibility.
  • Innovative features abound, and they're all very functional.
  • TXC compressor, in particular, is a stunningly versatile module.
  • Built‑in universal power supply in the portable V8 chassis.


  • Small module sizes result in cramped panels and hard-to-read legends.


A very versatile high‑end modular outboard system that can be used to build channel strips, multi-channel mic preamps, and even complete mixing consoles.


V8 Roadster rack unit £652; MP1A mic module £578; EQ4P EQ module £737; TXC compressor module £737. Prices include VAT.

Unity Audio +44 (0)1440 785843.

V8 Roadster rack unit $799; MP1A mic module $759; EQ4P EQ module $969; TXC compressor module $969.

Vintage King +1 248 591 9276.