Tag Archive | TB-303 clone

x0x, testing testing

In order to complete calibration and initial testing, I decided to make a temporary mounting solution for the x0x modifications. I chose to go with the following mods:

  • VCO: Slide time adjust
  • VCF: Resonance boost, VCO modulation, overdrive
  • Env: Variable decays, env. mod. amount, increase accent range, accent sweep speed
  • VCA: Bass boost, muffler distortion

Some other mods like ‘gate / env. on forever’ can be added at a later stage. At this point I was only interested with mods that affect the sound in some way. Need to hear whether I like a particular mod enough to incorporate controls for it to my enclosure design. The Pac-Tec cases with mods added on both sides of the top panel are f-u-g-l-y (so steer clear from that shit :P).

The modification controls on a temporary mounting solution :)

Calibration in progress..

Following the instructions from the x0x wiki, calibrating the analog side was a snap. The digital side.. well, crap. The buttons and whatnot behaved like the microcontroller (MCU) is on Valium..  No wonder why; a bit of poking around with the oscilloscope revealed that it’s running at a wrong clock rate! Nothing else visible that might cause the problem, so I’m guessing the internal setup options (aka ‘fuses’) for the MCU are not right.

Looking around the Ladyada forums revealed nada, the topics there seemed to mostly revolve around basic “Hi I’m a n00b” type of stuff. So, where to get the proper setup options??

Looks like I have a bit of testing to do..


x0x, test assembly #1

With the button cabling sorted out, I focused immediately to assembling the keyboard and making a test assembly. This is good for testing the buttons/LEDs and their cabling for functionality. I also get to verify some mechanical clearances to base further decicions about the enclosure on.

Test assembly #1.

For the panel, I simply printed the basic x0xb0x panel layout to paper and transferred this to a scrap piece of clear acrylic. This is a quick way to get the drill holes roughly to appropriate spots, perfect for mockups and such. Once potentiometers are wired this test assembly should also be good for testing / calibrating the mainboard.

Sideview of test assembly #1

Another sideview of test assembly #1

Of course, I had to do a bit of testing with the LEDs as well :).

This is what a green LED looks like..

..and a orange LED.

Above, you can see how the LEDs are installed on top of the switch. A button is fastened to the top panel and a clip-on mounting flange is attached to it. Finally, the keyboard PCBs is fastened to the flanges with screws, leaving the LEDs inside the hollow button shaft. In case you’re wondering “what flanges?”, they’re the beige ones slightly visible under a button. The first side view picture on this post shows them slightly better.

Also, on the picture above, the button lenses are not yet installed (hence the recess on the surface). A decal can be inserted under the lens, so I’m thinking of printing graphics on a overhead projector slide. This way, the step buttons will have numbers on them etc.

x0x, keyboard stuff

Time for some photos with this project! I didn’t bother documenting the PCB assembly, as there really isn’t anything worthwhile there. Just place the components and solder away.

For the the keyboard buttons, I chose to go with recycled ones from Series 92 by EAO. These are industrial grade buttons, so despite being used they’re still very good for home use and will certainly last a long time. As I happen to have plenty of used buttons of this type in black and white (and with PCBs for switches), I figured I could do a black and white “piano” keyboard with them. Maybe even paint the top panel in a similar fashion :).

With these buttons, it’s also possible to install 3mm LEDs inside the button shaft, thus making the top panel appear less crowded. For these, extra through holes had to be drilled to the PCB..

Extra holes (the countersunk ones) for the button LEDs on one of the keyboard PCBs.

To avoid making short-circuits to the bottom layer (GND) of the PCB with the LEDs, I widened the through-holes from the surface of the PCB with a countersunk drill bit.

As the keyboard switches have to be installed to a separate PCB, I decided to make the keyboard and x0x PCBs detachable. This was implemented with recycled floppy ribbon cables that I cut roughly to match the button spacing on the x0x PCB.

Floppy cables cut to varying length.

.. weird looking cables, but once installed:

Cables installed to the x0x mainboard.

Once completed, the connectors on the keyboard side should align horizontally (hopefully lower overall profile) with the connectors on the mainboard.

x0x, on with the build

Finally! Received the x0x PCBs in the mail last week!

The whole order came close to being cancelled and the plant also shipped faulty boards.  Luckily they were quick to replace the faulty ones.

The rare parts turned out not too difficult to source; I’ve been all set on that end for some months now and just waiting for the boards to arrive. Even got a bit lucky dumpster-diving and came across some working transistors that are used in the original TB-303. So now, it’s on with the build!

Huge thanks to Sasha for organizing the whole thing and pulling through!


Spotted a group order for x0xb0x PCBs at the Midibox forum some days ago, looks like I’ll soon have yet another incomplete project on my to-do list \:D/.

Image courtesy of ladyada.net

Whilst waiting for the boards to arrive, I reckon I’ll get started with sourcing the rare parts..