Vintage Boss Distortion - In More Ways Than One!

The Boss DS-1 Distortion pedal has a very mixed reputation. While it wasn't one of the first three small form-factor effects pedals released by Boss like the Spectrum I posted a couple of days ago, it's almost as old - dating to 1978. The major difference is that the DS-1 distortion pedal has been in continuous production since then. So why clone a pedal that's in production and can be had for low price of $59 at Sweetwater? In 1994, the pedal underwent a major revision necessitated by the discontinuation of the TA7136P IC pre-amp chip (that wasn't even actually an op-amp). The re-designed and re-voiced pedal is regarded as, in AionFX's words, "a poor quality beginner's pedal." For that reason, most modern clones are designed to capture the pre-1994 version of the pedal, which does generally go for over $200-300 on reverb, or one of the myriad of modifications that have been made to the pedal over the years, or both!

For this particular build, I ended up going "legacy" in more ways than one. This is the AionFX Comet project, but it is the legacy PCB. The PCB is stand alone, and does not include the bypass PCB characteristic of the more recent projects. However, while there is an updated version of the project with that, there are a few features unique to the legacy PCB that I wanted to take advantage of in this build. First, as you can see in the center of the board, the legacy PCB allows use of a TA7136P IC. I found one on Build Your Own Clone's website, and thought I'd give it a try. I'm not sure it's even genuine, but the whole point of this build was to experiment. Second, the legacy PCB provides the option of using more electrolytic capacitors, which can contribute to a more vintage sound.

The legacy Comet project is listed as an "Intermediate" build - just like many of the other more-recent Boss pedals (the updated version is an "Easy"). Incorporation of the diodes is a bit tricky as they have to be put on end. The default configuration is to have two diodes in series to provide the correct clipping threshold as the original 1S2473 diodes are hard to find. I ended up using BA282 diodes which were closer to the originals and didn't need a second diode in series. Based on my resistance measurements on the board with my DMM, that seemed to indicate I'd need jumpers in the other positions, though the instructions didn't call for it. I put them in anyway, which based on how the pedal works appears to have been the right call.

There is a clipping switch that lets you change from the conventional stacking diodes to an alternate configuration like LEDs. I went ahead and added them as well (as you can see in the bottom corner of the PCB), but at this point I'm not hearing a lot of difference between the no diode mode (switch in off) and the LED mode. That may mean that the effect is subtle, or it may mean they're not working properly.

As you can see above, there is a lot of blank space on the PCB as well. IC2 is for a more modern op-amp version and its associated resistors and diodes. The CX and DX locations are for adding a Big Muff Pi clipping stage ahead of the op amp. As I wanted this build to be as close to the original as possible, I left those slots open.

For the enclosure, again I've gone with something that looks a lot like the original. It's a bit different than the other AionFX builds because of the alternate placement of the LED. Of course, this is where I actually ran into the biggest problem on this build. The drilling template for some reason was a bit off when I ran it through Photoshop and took measurements, so I had to lock the PCB on the SPDT switch and then rotate the potentiometers (and bend the legs) to line up with the PCB holes. That wasn't a huge deal, but then I realized that since the original drilling template was set up for side input/output, there wasn't a heck of a lot of space to include top mounted in/out. In fact, if you look at the PCB, you'll realize that there is a gigantic electrolytic capacitor and transistor uncomfortably close to where the input jack needs to live. Fortunately with a little judicious work, I was able to get the jack situated to where I still have 1-2mm of clearance around the components. I should have taken a picture of the inside, but it is a bit frightening! 

With all of this work to get a vintage sound, I was really keen to try it out. Of course, as I went through the parts BOM, I found I was missing a couple of components. I didn't have any 250pF film capacitors, but I had a few 270pF, so I used them. I didn't have a 150pF film capacitor, so I had to use an MLCC. I'd hoped to use electrolytics everywhere I could, but was short one 47n electrolytic capacitor. When I hooked everything up to my tester, the light came on, and everything was looking promising. Then I tried it with the guitar and got nothing. I thought I may have a grounding issue (since there were two ground wires going into the alligator clip) - so I reset the ground and boom! Lovely, lovely distortion - especially in what should be the conventional stacking diode mode! 

This was an unexpectedly challenging build for a lot of reasons - the unfamiliar layout, the older style board and instructions, lack of a few components, and my general lack of foresight on getting the enclosure set up and drilled properly, but somehow it came out sounding great! I do plan on building some of the updated PCB versions of this pedal in the near future, as I really want to understand the difference in tone.