A Different Blues Driver Mod!

I've previously built a few versions of the Galaxie mod of the Boss Blues Drive BD-2 pedal. The most common of which is the version I'd sold as a part of Steggo's ongoing support of Ukraine's defense. There are other versions of the circuit out there, and I'd at one point (in the sadly far too distant past) gotten a request for the Keeley modded version of the pedal. A quick search of the internet showed that one of my favorite sources of all information pedal, the Tone Geek, had a write-up detailing his version of the Keeley mod (as it was used by John Mayer). I thought this was a great start, but decided to see if I could take things just one or two steps further. So here's Steggo's take on the Tone Geek's take on the Keeley mod of the Blues Driver. 

For this build I'm using the amazingly efficient PedalPCB Cobalt Drive PCB. Based on the product code, this is likely one of the earlier (early-ish?) boards laid out, but it still has all of the hallmarks of a PedalPCB board - that is to say it is extremely well laid out and makes the most use of all available space! It is also a bit unusual in that it is set up for 3.2mm 1/8 Watt resistors. I'm paranoid, so I went with 3.4mm 1/6 Watt resistors in my build. All of the resistor values are stock, the changes come when you get to the capacitors and diodes.

Most of the film capacitors are unchanged apart from C14. The Tone Geek's version includes the "fat" mod which gives the pedal a bit more bass. He incorporated a 33nF and 68nF capacitor in an offboard SPDT switch in place of the stock 18nF. As there are some versions of the "fat" mod that go as high as 100nF, I decided to go one further, my switch incorporates three capacitors (two 33nF and one 68nF) which gives me 33nF, 66nF, and 101nF in the three positions. In the future I may experiment with other values to include a stock 18nF in the mix. The modification also uses silver mica caps in place of the standard MLCC caps - though they were a bit of a tight fit. There is also one bipolar electrolytic capacitor used in place of the normal polarized one (C20). 

The clipping diodes are also modified in this version of the pedal. One of the 1N914 diodes is removed entirely with a jumper - visible in the upper left hand corner of the PCB. Two of the 1N914 diodes are replaced with 1N4002 diodes as well. Given how tight the board was, I had to mount these at an angle into the PCB, but they fit! The rest of the parts are unchanged from the original BOM. There are a total of seven transistors in the circuit: four J201, two 2N3906, and one 2N3904. There is also one TL071 which is socketed. 

Because I located the SPDT switch for the "fat" mod where the LED would normally fall for this enclosure, I moved the LED to the bottom of the enclosure and used one of my 3PDT daughter boards. Per my normal practice, the main PCB and daughter board are connected with ribbon cable while the jacks are connected with aviation grade wiring. All of the jack connections are insulated with heat shrink tubing. 

I had to come up with a fun enclosure for this design, and I decided I hadn't featured the T-rex enough on Steggo pedals (though Rexie has been a good sport about it). So for this pedal I went with the "Jurassic Drive" using some licensed stock art to create a feel of the movie without running afoul of copyright!

No sudden but inevitable betrayal here - just great tone!

The pedal sounds very good overall, the drive comes on strong fairly early and you can easily get above unity volume. The bass response is also very strong owing to the fat mod. However, you still get good treble coming through if you get the knob above noon.