x0x, sounds!

I promised myself that once my x0xb0x is in a fully functional state, the first thing I’ll do with it will be a cover from a song that I consider to be _THE_ acid tune of all times. So finally, after a lot of trial and error with the x0x build process, here’s my rendition of  “Acid Tracks” by Phuture (1987 / Trax Records). Press play on the player below and read on!

Little Bitchard – Acid Trax

After getting rid of the unstable keyboard design, it turned out that the new (otherwise functional) MCU on the mainboard was not outputting data signals used to create the CV at all. Sequencer was running fine though. Given the completely ESD-safe environment that I work in, it baffles me to high heaven at which point this fault might’ve occurred. The MCU could’ve also been already damaged when I received it (improper handling at the shop/stock), but I find this highly unlikely. Anyway, whatever the reason, after I got the new MCU installed, proper CV on the output of the D/A converter. Yay, I guess.

With the electronics functional, I moved on the sub panel layout. At first I mounted the potentiometers directly to the mainboard by bending their soldering pins at a 90 degree angle, but this seemed to cause random contact problems inside the potentiometer when it was operated. Too much mechanical forces pulling the (cheap) part in different directions, I guess. But cables it shall be then!

First version of the sub panel.

If you compare the picture above with my first test assembly, you’ll see that the appearance has changed quite a bit. I wanted to incorporate the x0x mods in a way that the synth will look like it was designed to be that way (and not a fugly kludged PT-10 piece of shit), so the mod controls are placed on their own row above (and aligned with) the standard controls. Taking this approach also meant that not all mods could be included, so I chose a selection of mods I liked the best. In the current design I still have the bass boost mod installed, but I’m thinking of removing it. As the boost seems to make very little difference to the overall sound, I’d rather have a clean panel than clutter it with pointless controls.

Muffler distortion schematic. Image courtesy of x0x wiki.

The muffler distortion mod also came close to being tossed. At least on my x0x, the output from the synth (at negative pin of C38) is not at a level high enough (below 1Vpp) for the clipper LEDs to do anything. However, once I installed the VCF overdrive mod, the signal level boosted close to 5Vpp region and the diodes started working their magic. Distortion on distortion <3

Strangely enough, with the type of potentiometer I chose to use, a 1M log value (needed for env decay control) wasn’t available at all so I had to settle for a different type. This of course meant that the potentiometer didn’t fit to the sub panel with the rest of the pots. Luckily enough there was enough free space where the potentiometer should be installed (no traces routed under the part etc.), so I drilled a hole through the board and mounted the potentiometer there.

Envelope decay potentiometer mounted on the mainboard.

As a sidenote, having this kind of installation option for potentiometers might be a neat extra. This would eliminate the need of a sub panel altogether, but it’d also mean a complete board redesign. In such a case, I’d probably go for 1206 SMD resistors and decoupling capacitors too :)


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