Solder Kong DIY Analog Synth and Guitar Electronics

From Big Cheese to Great Cheddar to Queso Blanco

Introduction

This year I relapsed, giving in to the fuzz pedal fetish that I had successfully shaved (dooh) after years of TV and video game therapy. It was an accident. For the past couple of years my wife and I have been minimizing our possessions and organizing the things we wish to preserve. I cut open a box that has been closed and stored for a couple of moves. Capacitors, transistors, switches, jacks, oh my. Many of these parts were ordered several years ago for a GEOFx project syndicated on the General Guitar Gadgets website: The Great Cheddar (any similarity to the Lovetone Big Cheese is not my problem)

Since I shaved my pedal fetish I have built a few more ambitious electronics projects, so I proceeded with arrogance - like Rocky Balboa in his first bout with Clubber Lang. Everything turned out okay (after too many hours), and I have documented the beating I took on my way back to my DIY electronics throne - i.e. the broken office chair in the garage.

Rebooting an Old Project

The first time I started this project I got a head start on screwing it up as I incorrectly scaled the PCB image on my toner transfer paper printout. The tone mode switch solders directly to the circuit board, and since I could not re-scale the pinouts on the 3P4T switch, I printed the PCB and re-etched the board.

Figure 1: Initial PCB

Even after filling in some of the poorly transferred trace images with a permanent marker, I ended up with a few bad traces that I bridged when I soldered. I forgot to use masking tape to secure the toner transfer paper to the circuit board when I "ironed it on." I also forgot to use appropriate heat settings and press down firmly. Finally, I forgot how I used to do such a good job of fabricating circuit boards.

Figure 2: PCB closeup detailing broken trace

Next I had to sort through all of the Mouser and Small Bear Electronics parts bags that were in my box of old parts.

Figure 3: Part sorting

I realized that back in the day I ordered the wrong value capacitors - all of by a factor of 10.

After a few humbling mistakes I was ready to proceed with the PCB.

PCB Soldering

Parts soldering is my favorite part of the process and I ran into no substantial issues there. I did, however, bring forward mistakes in the PCB that were corrected while the parts were already soldered - not a great idea for several reasons.

Figure 4: Mostly complete PCB

As illustrated in Figure 4, there is too much unused space on the edges of the circuit board. I was too bashful when I cut this board and had assumed there would be enough room in the Sovtek 1790NS enclosure I selected - though this was an invalid assumption as I added a battery drawer. So, I broke in my new dremel tool by grinding the edges.

Figure 5: Finally getting to use my new Dremel

Figure 6: PCB after grinding the edges

I do not like the idea of securing the PCB with only the switch, so I added holes on each side of the circuit board to accommodate PCB standoffs - later I ended up eliminating one of them by grinding its side down to the edge of the PCB trace.

All things considered, the PCB didn't turn out too bad. Grinding a circuit board with parts attached is careless though. That switch collected all sorts of dust that luckily was cleaned out by my air compressor and some contact cleaner. I'm lucky that I didn't damage some of the other parts. One thing that I did do right - and something I habitually do - is using transistor sockets and PCB sockets. Those are both critical components in these stompboxes and it's nice to have the option to swap components or replace bad components. It's also a great way to avoid applying heat to the transistors and ICs as they are installed after everything else is soldered. Having the transistor sockets was especially useful in this project as is discussed in the Testing Section.

The Enclosure

I selected a in the Sovtek 1790NS enclosure from Small Bear Electronics. I had originally wanted a larger slanted box (like the Lovetone or the Moogerfooger enclosures), but decided to go with a less expensive option. I decided to try installing a battery door for the first time - another excuse to use my new Dremel. My initial cut was very sloppy.

Figure 7: Botched battery drawer hole cut

I cut such a wide hole that there was no space left to drill holes for the battery drawer. I remedied this by attaching some small PCB board pieces to the interior enclosure with epoxy.

Figure 8: Fixing the battery door whole (too wide)

This solution worked surprisingly well and renewed my faith in the spiritual healing powers of superior adhesives. Next I had to remove more traces of my botched cut job with some bondo.

Figure 9: Bondo mess

Figure 10: Bondo mess

I had also screwed up a top hole that was originally going to be for a screw for the PCB standoffs - I decided to use my newfound epoxy idol to fasten the PCB standoff.

Figure 11: Bondo mess

If you've never worked with Bondo before and want to give it a try, pick a day to do it that you have a patient disposition and may be amused by fantastic messes. This stuff dries very fast so be ready to apply as soon as you mix it with water and do not mix too much at a time. Finally, after lots of sanding I had a pretty good fix to my drilling/cutting issues and some very dirty hands.

Figure 12: Bondo after sanding (that stuff is magic)

Figure 13: Bondo after sanding (top hole fix)

Figure 14: What happens when you don't wear gloves while you sand

Paint

Next I primed the enclosure and prepared to paint.

Figure 15: The first ill-fated primer coat

This is also where more craptastic botching occured as I decided to do some trimming around the driveway, forgetting that I had wet primer drying. Unfortunately I was too angry to snap photos of the terrifying mess that occurred when I removed the primer with steel wool and acetone - think my fuzz face is meeeelllting. The bondo absorbed some of the moisture and this caused some cosmetic issues in later painting stages. I also made the mistake of spraying too close to the box and perhaps not shaking the can enough. It took quite a lot of sanding and re-coating to get a satisfactory finish.

Millennium Bypass 2

I decided to give RG Keen's (GEOFX) Millennium Bypass 2 a try as I'm usually too cheap to buy the 3PDT switches for LED + true bypass. Keen's instructions and circuit analysis are detailed and insightful. I free-handed the PCB design and etched a very small circuit board.

Figure 16: Sketch of Millennium 2 board traces

Figure 17: Millennium 2 Board (left) after etching. Compressor board for another project (right)

Though the parts are soldered on the copper side of the Millennium board, I carefully drilled shallow holes for the component leads using a peck chuck on my drill press.

Figure 18: Drill press with peck chuck

As RG Keen suggested, I used the collector-base junction of a 2N3904 transistor as my "low leakage diode." It turned out very nice and will be illustrated later in the article.

Decal Design

I dubbed my Great Cheddar clone, The Queso Blanco. I bought only one sheet of decal paper and worked hard to get this part right. I started by scanning the face of my drilled enclosure on a flatbed scanner. Then I used Photoshop to make an approximate placement of my graphics. To preview my placement I printed the design on transparency paper (overhead transparency paper) and cut some holes.

Figure 19: Testing decal placement with transparency paper

Getting the placement of the switch labels (Dice, Slice, Melt, Shred) was tricky, but I got it just right after one round of revisions.

Figure 20: Applied decal

You can see a spot in the top right corner where the decal stock tore and the coloration is slightly different. This was the first time I had tried applying the whole face as one decal and the result was better than past projects where I cut each graphic/label separately. Decal paper stretches and tears very easily so you must be very patient and careful during this process.

Figure 21: Decals applied to the bottom enclosure plate

You can also see what a difference it makes with regards to blending if you compare these individual decals on the bottom vs the whole face on the top. I suspect that this would have been less apparent given a darker color, but hey, it's the Queso Blanco, it's gotta be blanco. I wish I had left the peppers and maybe even the cheese icon off, but I'm still pretty happy with the design.

Assembly

Figure 22: Gut shot

The guts fit comfortably in the enclosure with room to spare for managing wires. The PCB standoff provided a substantial improvement to stability and reduces the possibility of board jitter in the case that the switch nut is loose. The battery drawer is also a very cool addition though the plastic seems pretty fragile. In the future I'll opt for a battery door instead.

Figure 23: Finished (back)

Figure 24: Finished (top)

I will probably replace the radio shack knobs later (I think they're too big), but they're okay for now.

Testing

After a false start (bad solder bridge) I sampled some Queso. It produced a mild overdrive that was rather disappointing. I carefully inspected the PCB and touched up a few solder joints, but was still not getting any fuzzy cheese. I reviewed the parts list and noticed the transistor options listed: BC549 or 2N3904. I replaced the installed BC549 transistors with 2N3904 and wow, what a difference that made. I'm not 100% convinced that the BC549 transistors I installed were the correct parts - maybe there was something I neglected. Anyway, after the transistor switch I was a happy boy and accepted the circuit as is.

How does it sound?

Versatile. The 3P4T switch provides options: tone bypass, mid scoop, mid boost, and crazy mis-biasing (for octave-ish fuzz sounds). I tried it through twangy single coils (SRV strat pickups and Jazzmaster pickups), hot humbuckers (EMGs), bass pickups (70s PBass and baritone guitar) with great results. It's like putting a different facial hair disguise on each guitar. It gives you the awesome fuzz tones you want while enhancing the tone personality of the guitar. The crazy mis-biasing setting (far right) is loads of fun and I made a good gated sort of fuzz bass recording with it. If I were still gigging it would be tough for me to decide whether I wanted the Queso or the Foxx Tone Machine.

I'll post some audio video recordings in a future update.

Conclusions

I made several mistakes on this project and suspect that my subconscious planted errors to prolong the project/fun. I promptly planned the three next stompbox projects and am enjoying those too. When I'm too cheap to buy more parts I can always mess up something that I already finished and try to fix it, spill my organized parts boxes and re-organize them, or take a nap.

Acknowledgement

Thanks to RG Keen (GEOFx) and JD Sleep (General Guitar Gadgets) for generously sharing their knowledge with the DIY community. Both sites are highly recommended resources for anyone interested in building stompboxes.