x0xi0 #330-133.5 : Custom I/O Full

Finally back in the game. A solid draft of the documentation finally made its way to the ten of us using these PCBs so some of us are getting a head start while the manual is being finalized.

This build approach is different since one drops each component in by type first. I'll need to do testing later because the boards are really only populated fully in the in the end rather than being able to test sections incrementally. This concerns me a little bit because it may complicate troubleshooting. The documentation may eventually include test procedures in phases but we'll see.

Note that my own sourced parts, namely the resistors, are also 1/4W instead of 1/8W. I purchased all my parts before getting the mod kit. I hope I don't kick myself later for replacing them with the smaller ones. It appears I have clearance in the I/O but it's also quite obvious that the through holes and spacing on the PCB were design for 1/8W.

x0xb0x SS#01:Tweaking

One of the things I noticed with my x0x was that it wasn't *quite* a 100% match to the 303 sound I knew. The resonance wasn't quite there and it had a slightly harsher sound to it. The forums cover this in great detail so I won't repeat it all here but I'll touch on a few points that affected my x0x.

The biggest, most immediate change I noticed was swapping Q11 from a 2SC536F to a 2SC945. This noticeably muffled the sound but warmed it up. The harshness everyone describes can be eliminated right away via this transistor. The muffling effect it produced could also be adjusted via TM3, the VCF trimpot, so the range could match an original 303 with the 945s in them. I trimmed this pot after the swap and was able to match it to the real 303.

Secondly, the resonance level needs to match. This is such a signature to the 303 that's it's a must have feature. If the betas are too low in Q8, Q9, and Q10 it doesn't "scream" enough. I have to admit that I found it lacking in mine too. I started by swapping out my 2SA733Ps to 2SA733APs. The APs are found in all original 303s. Unfortunately it didn't have any audible impact for my x0x. As such I dropped the Ps back in and left them. What *did* work was adjusting the resistance in r97. The stock version calls for 10K. I found the sweet spot on this unit at 9.2K. This produced a perfect match with resonance at about 90% and left 10% more for me that exceeded what my original 303 had here. Some people add an extra pot to make this variable but I don't see the need. This produced what I wanted and still kept my 733Ps in use without using "fancy" APs.

During this tweaking I ran A / B comparisons the whole time with matching patterns and I can say that it is SO close to a match now that it's scary. For most ears it's an inaudible difference and in real world use it won't be noticeable. I can hear very, very small differences but it doesn't affect the overall performance and cloning ability of the x0x. This unit is without a doubt a near perfect match to the real TB-303 on my desk here.

So, to round up, it's at least three key steps:

• Q11: swap the transistor from a 2SC536F to a 2SC945
• R97: Reduce the resistor value from 10K to 9.2K (though subsequent units, or your unit, may be a different value)
• Adjust TM3 to match the cutoff setting to your preference. In my case my preference was the TB-303 I had here.

x0xb0x SS#01:Sequencer Part 2

I finally got my hands on the missing 16 pin DIP sockets and wrapped up everything in the x0x except the LEDs. Tack on another $3.45 in parts (6 x $0.50 plus Tax) which is not the end of the world but is thievery compared to the $0.07 / unit price from Futurlec. Lesson learned!

The manual isn't kidding about this being a long process and things getting tight in spots. I would have preferred to do all the resistors first (like they always say!), then caps, then dips and switches. It would have made life much easier. In any case the job got finished. Now the only task left is getting the LEDs set up and building the jump wires before we get to start closing this thing up!

As mentioned in my previous post, I opted for these nice flat LEDs I picked up. I diffused a set of them with a dremel for comparison but I'm finding that the clear glass look with really high resistor values is creating a very slick, low blinkyness factor that I rather like. I may regret it because if it doesn't really work visually, I'll be ripping out and replacing 40 resistors. I really hope I don't have to do that. The x0x's LED size is quite large, 5mm, but with this set up the LEDs appear recessed and about 2-3mm in size. It's rather unique looking. We'll see how it goes. The resistors are in so it's too late right now!

These are really high MCD valued LEDs so the resistor values I found that worked for this set up were as follows:

Purple UV - 2000 mcd: 10K
Blue - 5000 mcd: 47K
White - 8000 mcd: 68K

Blue is being used for Tempo and the tools on the left and right side of the panel. White is being used for all the notes and Sequencer steps: 1, 5, 9, and 12. Purple UV is being used for the remaining sequencer steps.

These are pretty high values but it looks elegant. I *think* it'll work. Next up: jump wires and then those LEDs!

x0xb0x SS#01:Sequencer Part 1

Ah, the sequencer. This is where things start to get more creative (in some respects) as opposed to functional. Aside from going through a soldering frenzy - heaps of parts, all pretty much the same - this is the stage where we get to introduce blinky lights. I haven't decided on a final configuration, but I have three flat LEDs on hand: blue, purple UV, and white. I'm considering a combination of all three but it hinges on the enclosure style I implement. In any case, this first phase is simply to get the stock parts out of the way. That means soldering sockets for all the ICs, diodes, caps, and a good handful of resistors.

> Note: I discovered that I didn't order a full set of 16 pin dip sockets. I'm missing six. That's a pain. They were a bargain at $0.07 a pop from Futurlec. Now I have to pick them up locally at probably around $0.25 plus my time and fuel, an inconvenience more than anything. Ebay's certainly an option but with a lengthy delivery time. Either way this is a minor, albeit annoying, setback. It would be nice to see all the ICs in place.

A working x0x is on the horizon! Fingers crossed that the sequencer works! I would love to hear some real sound come out of this.