The Comet Distortion project is a clone of the classic orange BOSS DS-1 Distortion, in continuous production since 1978. It’s got a few things going on in the circuit—the pregain and tone sections are very similar to the Big Muff, while the diode-to-ground hard clipping is similar to circuits like the Distortion+.
The DS-1 had a major circuit revision in 1994 that dropped the original single op-amp in favor of a dual, along with some other changes to accommodate. The original “Made in Japan” version is very well-regarded, while the revised “post-1994” version is not as much. However, it is one of the most frequently-modified pedals out there, with great mods available from Keeley, Analogman and Monte Allums. The circuit itself is a good one—it just suffers from cheap components.
The Comet Distortion will allow you to build either the pre- or post-1994 versions of the circuit, as well as incorporating most of the popular modifications.
The classic orange DS-1 Distortion has been in continuous production since 1978. It was part of BOSS’s second release of compact guitar pedals, after the OD-1 OverDrive, SP-1 Spectrum and PH-1 Phaser which first hit shelves in 1977. The other pedals in this second release include the CS-1 Compressor, GE-6 Graphic Equalizer and TW-1 Touch Wah. As a point of trivia, of all the BOSS pedals released in the 1970s, the DS-1 is the only one still in production. The next one to survive is the SD-1 Super Overdrive from 1981.
The circuit remained unchanged until 1994, when it was modified to use the new PSA adapter instead of the old ACA. In the process, the op-amp was changed from a single to a dual—still the SIL (single-in-line) form factor, but the circuit was also revised to take advantage of this newly-available op amp, and a unity-gain buffer was placed in front of the adjustable gain stage. They also made a few more component changes at this time as well, though they were extremely minor (see the Comet build doc for the particulars).
The post-’94 version is universally considered inferior to the original. This is BOSS’s cheapest pedal on the market at a typical price of USD $40, and so they have continually reduced the quality of the components (especially the op-amp) in order to maintain this price point. The original TA7136P op-amp sounds great in this circuit, while all of the ones they used after 1994 (BA728N, M5223AL, and NJM2904AL) are garbage. With the Comet project, you can use a modern DIP8 op-amp such as a JRC4558D or OPA2134, and these sound fantastic. So the poor reputation of the current-production DS-1 is largely a factor of the op-amp.
One more point to make in this section—often the original version is referred to as “MIJ” or Made in Japan, while the modern version is called “MIT” or Made in Taiwan. This is roughly true, but BOSS switched production to Taiwan in 1988 and the DS-1 was unchanged until 1994, so there are six years’ worth of Taiwanese versions that would still be considered the “good ones”. The country of production is not an accurate way of deciding whether it’s good or bad—it’s more accurate to call them “pre-1994” and “post-1994”.