x0xb0x SS#01: Adjustments & More Tests

Today I set some time aside to address some of the outstanding tasks that were left on my list.

- I removed the BA662A and tested out a BA6110 in its place
- I drilled the power switch hole into the back of x0x
- I cleaned up the knob heights and properly aligned the rotaries. The dremel work needed to be straightened.

What's left:
- Replace the tempo encoder. The shaft has loosened due to my dremel work
- Drop in the heat sink once and for all
- Paint the back, possibly the enclosure
- Wipe down the top panel so it looks fresh again

The BA6110 is a perfectly good alternative in my view. It's nice to have the BA662A in place for the sake of authenticity but frankly it doesn't sound any different. I've left the BA6110 in place for now to put it through several months of jamming.

x0xb0x SS#01: A/B Comparison

I finally got around to doing an A/B comparison of my x0x and a TB. The TB plays through the left channel; the x0x on the right.



I still need to finish up some of the cosmetic elements of the synth but the delay is largely in part to me preferring to jam with it :)

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:Testing & Tuning

All the parts were in place; I was soldering and building the x0x carefully; I certainly spent enough time on it. I couldn't figure out why the x0x wouldn't fire up. I compiled a list of all the tests and went through them once more as a matter of quality control. I completed a battery of tests and got support through the x0x forums and covered everything from my power supply to each IC in the digital section of the pcb. It turns out that my earlier envelope issue was still at the heart of the problem. It was still causing errors and wasn't sending the correct voltage to the amp. After about 2 hours of troubleshooting I was relieved to discover that 2SC536F in Q37 was faulty. I replaced it with another one and low and behold it was fully functional! LIGHTS AND SOUND! Relief & Joy. It wasn't my shoddy set of skills. It was a dead transistor.

Hours of jamming and more tests ensued. I had the x0x drive a TR-606 and vice versa, Ableton and ACID driving the x0x via MIDI, and even had a connection to the c0ntr0l software.

After a good week and a half or so of just enjoying the synth I finally sat down and tuned it as well. It's by no means a complicated step but it does require a bit of patience. The forums suggest setting the tempo to its lowest speed, setting up a low C and middle C, both with long slides and decays and using a tuner to match it all up. This method worked beautifully for me via Wavelab 6 and a free tuner VST.

I must say that I thought the x0x sounded amazing when I got it working but hearing it tuned properly really makes it sing. *Now* we have an instrument here!

x0xb0x SS#01:Sequencer Part 3

The LEDs.

If there's any advice I could give to anyone out there who's about to embark on this step it is the following:

- Install your standoffs, washers, etc., first.
- Set up and just drop in your LEDs onto the board. Do not solder them in yet.
- Set up your top panel so that the height has been correctly set.
- Place easy to remove tape on top of the overlay panel LED holes.
- Set up each LED into their respective holes. Lightly stick them to the tape.
- Solder away!
- Remove the tape.

I suppose if you have the kit's LEDs or your own rounded LEDs this step may be relatively easy. Using flat LEDs is a whole other matter though. It just takes some patience and in my case, a few mistakes to get this right.

Regarding the standoffs:
It seems obvious now but no one wrote it down before so I'll do it now. The two standoff heights you're likely buying are 10mm and 15mm. The 10mm standoffs are used on the four outer corners. The 15mm standoffs are used in the center holes of the board. This prevents the pcb from bowing and keeps the height consistent! Obvious, I know!

Once I had the LEDs locked in I fired it up and .... NOTHING.

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.

x0xb0x SS#01: I/O

This was an exciting stage actually. First of all, it's nice to see several of these 'external' components land into place on the I/O board. 1/4", MIDI / DINSync, and CV / gate jacks all make up the familiar territiory of any synth and gear owner. This makes the project feel like it's really starting to come together. Secondly, the MASSIVE leap forward was downloading the Serial <-> USB driver and plugging the I/O into the computer. JOY!! I nailed the USB chip on the first go. Looks like the beer helped after all ;) The computer recognized the card and installed the drivers. As far as WinXP is concerned, this x0x is 'ready to use'. I'm elated!

Of course the x0x is far from complete or running an OS but it sure is encouraging!

x0xb0x SS#01: USB Chip

This was the step I considered to be the 'hump' of the build. I didn't have the I/O card shipped with the USB chip pre-soldered so putting this in place was going to be my big challenge. The 32 points would be my smallest solder work to date. I took my time, about an hour in total (clean the surface, place and solder, and snap pics throughout), and hoped for the best. The beer I had just before doing this probably calmed my nerves but also made me aware that I may very brutalize the whole thing. The true test will occur once the I/O is in place so here's hoping!

x0xb0x SS#01: Headphone

This was another painless step in the process. There's nothing to really test just yet according the documentation. That will follow once the I/O is in place. It's also nice to see the volume pot in place.I couldn't resist snapping a better pic of the BA662 I have too. I'm looking forward to hearing this amplified. The LA4140 also looks ancient despite being new old stock. It just looks vintage alongside some of the other old ICs. Note that I'll also be building the wiring for the jumpers.

Q33's hFE: 200 mfm*

Total time on this: about 2 hours to sort parts, build it, snap pics, and write this.

* My Faulty Meter

x0xb0x SS#01: VCA

The VCA was a reasonably painless step. It was really nice to see the BA662 IC get dropped into place. Seeing it on the pcb starts to give one the sense that the project is taking shape (despite upcoming steps being rather large).

Q31's hFE: 198
(again - based on my faulty meter)

Testing this section gave me some odd results. I was able get a change in sound behaviour but I couldn't say that it sounded like a note. I tested the resistors and got some odd figures here:

r127 (47K) : 39.4 K
r128 (220K): 52.5 K
r129 (2.2K): 20.25 K

The folks on the boards suggest that it's not entirely out of the ordinary and suggested I carry on to the sequencer to trigger notes properly, then troubleshoot again. I'll follow their advice on this one.

The parts for the headphone / mixer are set aside already. I'm looking forward to starting that.

x0xb0x SS#01: Envelope

Today's boost in the VCF results left me with no choice but to drop everything else I was doing and get building. I tackled the envelope section.

It took a short while to get organized, pull the parts and get soldering but all in all the whole process was quite painless. I still socketed all the rare parts too. The two 2SA733P were pulled from my lower measured bags:

Q38: 197 hfe
Q39: 196 hfe

These values are all based on my faulty multimeter though. That's the value I'm getting at this time so I'm keeping it here. I'll document it again properly once I have accurate measurements.

The tests were mixed though. I need to look into that. The first test was successful: 12 volts when connected to D35. D36 does created a pulse but not at 12V so I need to test again more carefully. I suspect it's correct though.

Total time on the ENV today: 3.5 hours including the pics and this blog.

-

x0xb0x SS#01: VCF

Wow. What a frustrating stage this was. I hit a brick wall and the project languished as a result. No point in adding day numbers to my titles anymore!


I put the VCF together shortly after the last blog. I took my time just as I had with the other sections of the x0x and thought I has put it together successfully. Once I began testing it I couldn't get a signal to confirm it was working though. I didn't have scope so I tried to whip up the diy audio probe that's suggested on the x0x build page. I fudged my through it but never really got it working properly or to my satisfaction.

Because this section of the x0x has several rare parts, I started to wonder if one or many of them were faulty. So I spent tons of time checking resistor values, voltages, betas, and the like, all with mixed results. I was sure something was wrong. At the same time, I thought it was high time to get a scope but I couldn't justify hundreds or thousands of dollars on a new one, and frankly, I didn't want yet another 50 pound tool in my arsenal. My hope was to track down a proper soundcard probe and use free software. Between these two challenges it took 6 months. It was really discouraging.

The GOOD news is that I had success with both of these challenges. First things first: I found a probe at a great price by Virtins. $30 US, shipping included to Canada. Can't argue with that. Once I plugged it into my line input on one of my low end sound cards, I wired it all up to the x0x, got testing, and low and behold: the damn thing seems to be working just fine. I just couldn't measure it properly.

I can't begin to express how relieved and elated I am to have past this step. I feel like I can continue and know that I don't have to revisit a problem.

On a side note, the OTHER good news is that I managed to track down 2SA733-APs as well so I'm that much closer to making an authentic 303. The critical components are right in the VCF: Q8, Q9, & Q10. It turns out my hFE reader on my multimeter is also crap so the component log component log isn't accurate either. (I always thought they were unusually low.) I'm going to leave them in and revisit this later. I need time to find a better way to measure these too but this less important than starting to solder again!!

A real Sight for sore eyes:

The VCF test with the cutoff and resonance at 0%.



The VCF test with the cutoff at 100% and resonance at 0%.



The VCF test with the cutoff at 100% and resonance at 100%.