Z0XB / Z0-XB


When experimenting with different music setups I started to realize that at I needed an analogue bassline. I was tempted by Doefpers Dark Energy, I was looking for Access Virus in a decent price (ok, I know its not an analog but it would do) but in the end I found myself unable to resist a classical TB303 sound. Roland Transistor Basline and a drum machine was all you needed to make techno in the90's (downloadPropellerheads ReBirth to be able to experience that ability again).
The problem with TB303s is that they get ridiculously expensive theese days, even versions that dont have MIDI IN retrofit (tb303 was one of the lase machines of the pre MIDI era).
There are countless machines out there that try to emulate that classic 303 sound (hardware: Future Retro Revolution, Acidlab Basline, software: Audiorealism Bassline, D16 Phoscyon) and many many others) . In theory it shouldnt be too complicated. Two waveform monosynth (square, saw) with a single envelope generator controling a 18dB/oct lowpass filter. Add accent and slide and a 16 step sequencer and you,ve pretty much covered all the featured of the original. The problem is they dont sound exactly the same. Many get close, some even extend the sonic possibilities, but for many enthusiasts similar is not good enough.

Introducing x0xb0x

Thats why a adafruit team, lead by ladyada, a charismatic female geek from MIT, have spent signifficant amount of time reverse engineering the original Roland synth transistor by transistor and re-designing it to allow construction using elements that are still possible to get (the production of many of the original parts has stopped some twenty years ago). Adafruit has prepared and sold somewhere around a thousand of DIY kits, but as their whole project was Open Source from day zero, there are other entities out there producing PCB boards, front panels, and complete devices. The x0xb0x is well documented with active community and considerable knowledge base including wiki pages where you can find mods and people discusing theories on how does a specific section of the unit work (which is not always obvious as we are dealing with voltages and currents pasing through hundreds discrete elements, not code).


z0xb0x is a pet name of my x0xb0x. It's actually three devices combined: x0xb0x,Boss OS-2 Distortion/overdrive pedal and DMF-2 a low pass high pass filter.

Overdrive seemed like an obvious addition, most people run their 303 through some overdrive distortion pedal anyways, but I didnt like the fact that distortion always adds higher harmonics, so I added the DMF-2 to serve as aditional low-pass cuttof knob. Everything is contained in one unit (pictured above), and although I did not manage to work out a way to power all three using only one power supply (it uses two power supplies for full operation) it is still a signifficant cut on cabling noodles and desk space (z0xb0x is a signle box that needs two power supplies and a signal cable to the mixer - with all thre devices seperate it would be three boxes, three power supplies and three cables to think about each time I set up). As a bonus I got a highpass filter too which has proven useful to cut the low base when playing alongside a DJ- when the track is already full of bass it is not always a good idea to mix in more low frequencies, whereas more often than not you can squeze in some more overdriven acidic bites. When playing with a dj its good to have some sort of audio-to-midi-clock converter, I use SoundBite Micro from Red Sound but there's plenty of other options.
I must admit, I wanted to save myself some time and effort by skipping the build of my x0xb0 (which can take anything from a couple of days to a couple of months depending of how comfortable with soldering iron you are, and how likely are you to keep focused enough not to confuse any resistor values or diode polarities all the way throughout the build (and there quite a few discrete elements to solder in).
That's why I got a used, ready made x0x off ebay. I hoped to skip the messingbaround part, it wasn't long after I got it I discovered that something wasn't quite right. The resonance knob was only having effect in less thab 1/3 of its twist range and Decay knob had no effect at all. The seller stopped responding to my emails so here I was, searching the forum for answers. Out there I found a suggestion that both Decay and Reso potentiometers had the same physical form factor but radically different values (50k vs 1000k). Unsoldering them took a couple of hours, but was truly worth it - I bacame an owner of a true 303 emulator. As I had it open with a heated up soldering iron, so I was bound to do some more experiments while there.
At this point I have to thank al the people who spent their time documenting the process. I would recommend loking at Subatomic glue for his x0xb0x Mod guide, as he got a lot of good info compiled in there, without it I don't know if I would be bothered modding mine


Absolutelty first thing you have to do after buying a x0xb0x is loading SokkOS instead of default firmware. SokkOS has nothing missing and few great features like: selective looping, reverse, copying presets between banks, shuffle or half-speed mode.
One of the simple and obvious hardware mods I made was adding the ability to change the Env Mod down to zero, while at you can play with increasing the env mod range if you want to.

A lot of peope recommend a mod called Reso Boost, but I personally had some mixed results. Theres a range of resistors that efect the resonance and while you can change the amount by just changing one, that wil affect the tone character too. Thats why its critical to use a toggle switch with the mods to be able to go back to stock, 303 parameters. After some tests I discovered that I like the stock resonance the most so I ended up not doing leaving reso mod.

Very popular bass increase mod is popular for a reason. It makes the sound thicker, but affects the high resonance of the filter and interacts heavily with distortion mods so switch is a must.
Another good mods are amp envelope and accent envelope controls. I've added a dual switch to be able to go back to stock values, but I find the ability to shorten the notes to be the most creativity unleashing mod. The two knobs offer control over accenter and non-accented notes seperately, and with the shortest decay the notes are practically silent, so you can crossfade between two different melodies (if they have no overlapping notes).
Related to amp env mod is the filter atack mod. Not terribly expressive, allows smoothening the beggining of notes.
So called devilfish distortion mod is offers quite pleasing distortion (gets into interaction with bass mod). I didn't pay too much attention to values here, not nessesarily wanting it to be pure devil's ratio.
I have mixed feeling about filter modulation mod. It seems to sound far better when the xox is set to saw wavefoem, giving a bubbling quality to the sound, much less prenounced when applied to the aquare wave.
Ive added a switch connecting two random points on the board. Well, not exactly random but found ina circuit bending manner as a most interesting pair of points to short circuit.
Finally, as in my hardware only setup xox is used as a master clock, I've added a quick edit mod - a swich which purpoe is to jup in and out patter edit mode when xox is in sync out mode.