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Mode Machines Xoxbox

Analogue Synthesizer
Published November 2010
By Paul Nagle

Everybody, as Fatboy Slim so wisely notes, needs a 303. However, with originals becoming ever more scarce and expensive, the dream of universal 303 ownership was starting to look unlikely — until now...

Mode Machines Xoxbox

Not to be confused with the Xbox, the Ladyada Xoxbox (pronounced 'zocks box') first appeared around five years ago, initially in kit form. The quest to clone the TB303 was not undertaken lightly and involved matching components as closely as possible to the originals or sourcing modern equivalents. Perhaps the most significant advance over previous 'rack clones' was the incorporation of that vital, yet often omitted, element, the sequencer.

As not everyone has the necessary time or skill to complete a project of this type, a cottage industry was born serving up Xoxboxes in a variety of styles and finishes. It is one of these, professionally constructed by Mode Machines of Germany, that will bleep and squelch for us today. Or, rather, two, since both a red-LED and a blue-LED version were delivered — lucky me!

Xox It To Me

The Mode Machines Xoxbox, at 20 x 28cm, is bulkier than the diminutive silver Bassline it strives to be, although its black sloping plastic case is surprisingly light. It's peppered with LEDs (40 in total) and populated with generously‑spaced knobs and clicky buttons — the invitation to play couldn't be clearer. It's not unreasonable to suppose that as the buttons are brand new, they'll respond more reliably than those of ageing originals.

Other than the colour of the LEDs and a couple of the buttons, there was no difference between the models supplied, so I turned to the blue version for the fresh splash of colour it brought to the studio. Usually I find blue LEDs too bright for comfortable long‑term use, especially when there's lots of them together, but these are pleasantly subdued and quite mesmerising when the Xoxbox is in full flow.

A study in panel ergonomics, the synth controls run along the top and sequencer‑related buttons, including the mini keyboard, span the lower half. A row of LEDs divides the sections neatly, while directly above it, a 16‑way Function knob dials up the desired operational mode. An adjacent knob, also with 16 options, selects Pattern Banks, Tracks and other parameters that require numerical selection.

Taking a prominent place next to the master Tune knob is the saw/square waveform selector — a far better choice than tucking it away on the rear, which was the switch's fate on the 303. Actually, the Xoxbox's rear is busy enough. It has a full complement of MIDI ports, plus DIN Sync and USB and CV and Gate outputs, both on 3.5mm jacks. In regular quarter-inch format, there's the main audio output, an input and a headphone socket — leaving just enough room for the 9V AC power adaptor and on/off switch. Hopefully, it was a temporary oversight that the adaptor supplied for the review was in euro format.

Some entries from that collection of 'ins and outs' deserve explanation. What possible use, you may ask, could a TB303 clone have for a USB port? Actually, this particular USB implementation differs from that found on most synthesizers, and since it's a bit geeky, let's return to it later. For now, I'd like to run through the 'normal' connectivity, starting with the audio input. This isn't an input to the filter (as per the FAT Freebass, for example) but instead, and true to its 303 heritage, the incoming signal is merged with the Xoxbox's own. You may feel that is generally unexciting — until the day you run out of mixer channels!

In another direct lift from the 303, the CV and Gate outputs will drive any Oct/Volt analogue synth. If you have no such synths, the sequencer will cheerfully control your MIDI gear instead. Finally, anyone lucky enough to have been hoarding old Roland drum machines can rejoice in DIN sync, with the Xoxbox equally happy as master or slave.

Xox Appeal

The Xoxbox's rear panel. From left to right: 9V external PSU input, headphone out, 3.5mm Gate and CV out sockets, USB port, main output, MIDI In, Out and Thru, audio input and, lastly, a DIN Sync port.The Xoxbox's rear panel. From left to right: 9V external PSU input, headphone out, 3.5mm Gate and CV out sockets, USB port, main output, MIDI In, Out and Thru, audio input and, lastly, a DIN Sync port.

There can't be many (any?) Sound On Sound readers who are unaware of Roland's 'Transistorised Bass' and its story. Hardly the epitome of success on its release, the TB303 was a slow burner that belatedly provided the backbone of countless house, acid and techno classics. I still periodically slap myself for failing to grasp its versatility when I owned a couple of them back in the day — but who would have thought this single-VCO analogue synth with the most basic of envelopes and a slightly awkward sequencer would spread across the dance world like a rash? I'm clearly not alone: Roland abandoned them after just two years production in 1984.

Sonically, the Xoxbox requires no introduction, because if you've heard a TB303 or one of its better clones, you already have a good idea what to expect. Although Ladyada, creator of the Xoxbox, claim an impressive 99 percent of the components chosen match the 303, there will still be those for whom only the real thing, warts and all, will do. After a while jamming with the limited controls — cutoff, resonance, envelope amount and decay — I was convinced that any differences between a Xoxbox and a real 303 are of no more significance than the differences between actual 303s. It squeals, it cries, it emits deep, warm bass and it gleefully spurts wet, acid tonality.

What sets the Xoxbox apart from most other MIDI‑controlled 303 clones is its sequencer. Here you may have expected the 303's sequencer to be copied as closely as the transistors, but Ladyada took the unusual — and brave — step of 'improving' it. I say 'brave' because a massive component of the 303 sound arises from the way its patterns are formed, in particular the way accents accumulate, but also there's the strange randomness that occurs when batteries go bad, or are temporarily removed. This random memory scrambling often yields better patterns than hours spent toiling over the sequencer, so it's a relief to know something similar can be replicated in the Xoxbox with a mere button press. This is just as well, since the new boy has no battery: its memory is an onboard EEPROM that stores a maximum of 128 patterns (double the capacity of the 303) and 64 tracks, which are sequences of patterns.

Func Soul Brother

Everything begins at the Function knob, a seemingly packed circle of choices. Very quickly you realise that the commonly used modes can be grouped into either pattern or track‑related, then subgrouped into master or slave roles for either MIDI or DIN Sync. With familiarity, any perceived complication dissipates — it's all there before your eyes. I should point out that although the Xoxbox is a hands‑on machine, every change of function stops the music.

With the knob at 12 o'clock, you encounter the delightfully misprinted 'Pattern Syng Out'. In this mode, you pick a pattern using the Bank Select control and one of the eight white keys of the mini keyboard. Select another pattern during playback and it smoothly takes over on completion of the first. This behaviour, plus a simple transpose (via the up and down keys and mini keyboard) would accommodate many 303 users' needs for their live sets.

Tempo is set using either tap tempo (via the 'Done' key) or a notched encoder with a range of 20‑200bpm, each notch acting as a 1bpm increment. Since the Xoxbox arrives with its pattern banks blissfully empty, we should attend to that first by turning the knob three clicks to the right and entering 'Pattern Edit'.

Pattern Edit

The Xoxbox is available in two versions: with red LEDs and buttons like this one, or with blue LEDs and buttons. They are otherwise functionally identical.The Xoxbox is available in two versions: with red LEDs and buttons like this one, or with blue LEDs and buttons. They are otherwise functionally identical.

There are two ways (actually three) to begin spawning 303 patterns. The first requires that the sequencer be stopped, and involves then pressing the Next and Prev buttons to navigate through the pattern, while playing the required notes on the keyboard. When in this mode, the LED row reflects the current position in the pattern. Thanks to the Up and Down keys, you need not be confined to the keyboard's single-octave span, while accents, rests and slides should be employed liberally to bring your creation to life. Somehow, by judicious use of this handful of techniques — plus plentiful synth manipulation — the Xoxbox serves up grooves that are as valid today as at the height of the 303's fame.

A pattern may be any length from one to 16 steps. When it's long enough, press Done (effectively 'save”) and it's complete. To hear your creation in all its glory, press the Run button.

The second method of note entry is more dynamic and interactive. This time you press Run at the outset and, as the chase LED scurries along, notes are entered via the keyboard. You might want to slow down the tempo to make this more controllable — or you might be equally happy to embrace the chaos and see what happens! When recording notes in this way, you're free to add rests, accents, ties and transposition as you go. Naturally, all notes are quantised exactly to the beat (this is a step sequencer after all), so nothing can go drastically wrong. I found this far easier than the 303's own sequencer, and so much fun that I wished the technique was accessible during any of the 'pattern play' modes. However, as the keyboard is used for pattern selection, that isn't on the cards.

There's one last slant on pattern creation, and it's arguably the fastest and most entertaining of all. It definitely requires the least effort! With the pattern running, simply hit 'Chain'. When you're in Pattern Edit, this translates to 'give me a random pattern please'. If you don't like the results, hit Chain again. And so on. Soon I'd assembled a decent collection of material, having tamed the wilder excesses of randomness with the previously‑described edit techniques.

Should you be inclined towards elaborate musical arrangements, Xoxbox patterns may be captured into an external sequencer. Helpfully, all notes, slides and accents are transmitted faithfully via the MIDI Out port. The internal sequencer is fast and uncomplicated, and therefore an ideal scratchpad for use with other modules. Alternatively, the internal analogue synth can be played from an external controller or sequencer by selecting the 'MIDI play' mode.

Making Tracks

Having made a pattern or 20, you might want to go beyond the 16-step limit and string a few together. In any of the pattern play modes, the chain button is used to assemble temporary chains of patterns. These loop round and round, very much like the equivalent TB303 function — although the patterns need not be adjacent to each other to be chained.

For a more formal song‑like structure, you can store sequences of patterns. In Xoxbox terminology, these are known as Tracks. There are 64 tracks in total, each with up to 16 patterns.

In Track Edit, the Next and Prev keys are used to enter patterns in the order required, a row LED representing the position of each within the track. The same pattern can be featured multiple times and may be transposed at each step if necessary. When the track is complete, select one of the 'Track Play' modes and hit Run. In a nice parallel with Pattern Play, selecting a new track while one is already playing cues it to play next. In this way, the Xoxbox can handle quite complex, prepared structures, leaving you free to concentrate on making the synth growl.

Further Functions

The remaining functions are pretty self‑explanatory and relate to how the Xoxbox syncs to external sources or acts as master clock for MIDI or Sync24 operation. Of the less‑used options, 'Random' simply generates an endless series of random notes and the aforementioned 'MIDI Play' allows remote control of the Xoxbox synth, the bank knob setting the channel. There's also 'Keyboard', in which the tiny keyboard becomes a basic generator of MIDI notes.

I haven't yet mentioned the three user options, A to C — but there's a good reason. They are provided for anyone who wishes to dig in and add their own features; as standard, they don't do anything at all. This leaves just two final functions, both computer‑related, for which we must turn to the USB port. The functions are 'Bootload' and 'Computer Control', and they require your computer to have a USB Serial driver present — a driver my PCs, both running Windows XP, hadn't heard of. I promptly headed to the Ladyada web site ( and located the driver, along with a pattern editor (called Control), and installed them. There then followed a period of 'nosing around' to determine which port the newly‑added driver resided on. This information is required by Control before it can communicate successfully with the Xoxbox. I have to confess that I only got everything working properly thanks to the patient assistance of users from the forum — but once up and running, Control was able to grab and edit patterns, take backups or upgrade the Xoxbox's firmware with alternative operating systems.

The Control software isn't currently available for Mac, and I'm afraid it won't win any awards for elegance either, but it is the only way to back up your patterns right now. There are instructions on how to perform firmware upgrades on a Mac but I totally wimped out of trying them. Let's just say there were rather more steps involved than I liked the look of, especially as I wanted to press on and explore the alternative firmware kicking around t'Interweb.

Alternate Firmware

As the Xoxbox is open source, there are a number of alternate operating systems for it. I would definitely advise seeking the wisdom of experienced Xoxboxers, because there are clearly pitfalls for the unwary (Unwary is my middle name). I opted to sample the 'SokkOS' firmware, because it has a number of enhancements over the OS supplied by Mode Machines. Plus it comes with a fatter manual.

Installation took a matter of seconds, after which the Xoxbox gained a range of new powers. Amongst these are the selection of patterns using MIDI patch changes and an improved 'save' process, making it easier to save patterns to alternate bank locations. This OS doesn't insist on stopping when you switch between playing and editing patterns — one of a range of tweaks that (I felt) gave it an edge over the supplied firmware.

I quickly homed in on a personal favourite SokkOS addition, 'loop mode'. This playback‑related feature involves the 'Done' key, and keys to set the start and end points of a 'mini loop'. Since setting this loop requires 16 buttons, the 13 note keys plus reset, accent and slide (often called the RAS keys) are drafted in. If you pick a loop start with a higher number than the end — say you press button seven then button two — the pattern plays between those points, but backwards. At any time during performance, you can restart a loop at the first step, or restore the original pattern length, all without stopping the music.

Other SokkOS performance enhancements include the skipping or repeating of steps during playback, or exactly halving the tempo of a pattern, or adding up to five levels of swing. You can temporarily accent every note or globally switch in slides or rests — all tricks that extend an already playable sequencer without bogging you down in unnecessary complexity.

The only missing feature, as far as I could tell, is support for triplets. Apparently there is firmware out there in cyberspace that does include triplets, but I resisted seeking it out in order to finish this review. It goes without saying that, if the extras I've mentioned don't appeal, there's no need to ever consider upgrading the OS.


I admit I was one of those who totally failed to 'get' the TB303 the first time around — but that hardly matters: the interest in this classic synth has remained steady over the years. When it eventually became clear that Roland wouldn't satisfy the demand, others stepped up to the mark.

It's easy to see why the Xoxbox is regarded so highly amongst the analogue community, with only a few purists bemoaning such liberties as the 'fixing' of the sequencer. For some, the Xoxbox has attained a Grail‑like status of 303 perfection when, in fact, there are frequently wide variations between real 303s, especially as their components — never exactly high‑end choices anyway — grow older. So the concept of one ultimate 303 is highly misleading.

The Xoxbox does show evidence of its home‑brewed nature, most notably when it comes to the Control software, USB serial driver and the whole firmware update process. Of course you don't have to update the firmware at all, but if you are feeling adventurous, the SokkOS alternative is a worthwhile step forward, its extra functions blending in seamlessly without disrupting the core of the instrument.

Mode Machines have done a creditable job; their version of the Xoxbox is priced well below an ageing second-hand TB303 and sounds as authentic as you could hope. What seals the deal for me is the sequencer, offering the right level of hands‑on interaction and a randomiser worth its weight in gold. In pattern edit mode, the light show of LEDs dancing over notes, accents and slides is dazzling — and I'm a sucker for being dazzled. The Xoxbox therefore comes highly recommended as a perfect solution for anyone still seeking a TB303 or contemplating retiring their original to the safety of the studio.  


There have been a large number of 303 clones over the years, including first class software emulations such as Rebirth, but for the complete hardware package of hands‑on synth plus sequencer, a well‑made Xoxbox takes some beating. Many established alternatives, such as the MAM MB33, the SynTechno Teebee and the Analogue Solutions Trans‑Bass‑Xpress are no longer in production, so your choices aren't as wide as they once were. However, there are other ready‑made Xoxboxes to consider, for example from Technology Transplant.

Quite Interesting

'Q: What kind of filter is in a TB303?'

'A: It's 18dB, isn't it?'

Cue flashing screens, general ridicule and Stephen Fry's kindly voice... No. The filter is a ‑24dB/octave filter built from a diode ladder. It can be thought of as four ‑6dB/octave stages connected one after another. However, the cascading action isn't text-book perfect. Unlike the transistor ladder-filter, each successive stage of the diode ladder loads the previous one, producing a rounding‑off of the initial filter slope. So the filter tends to a ‑24dB/octave roll-off but takes longer to get there than other designs. This gives the impression of a brighter-sounding filter than typical four-stage filters. Indeed, close to the cutoff frequency, it does shows a similar roll off to a three-stage, ‑18dB/octave filter.

What is perhaps stranger is that Roland chose to use not diodes in their ladder designs, but transistors wired as diodes. Early Roland diode ladders used five stages, perhaps to more closely replicate the initial roll-off of a four-stage transistor ladder — you can find these filters in the SH2000, System 100 and others. Even so, diode ladders do sound different to their true transistor variants.

Finally, for further reading, see Thanks to Tony Allgood of Oakley Modulars for the QI answer.

Published November 2010

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