The Boss DS-1 is a relatively easy distortion pedal to mod if you have moderate electronics ability. The pedal is cheap to buy and has a 
simple circuit that produces a decent quality distortion. Although the mass-produced Boss DS-1 is one of the most popular distortion pedals on the market, the circuit has many options for modding to make it sound even better. By simply swapping out some or all of the capacitors, resisters and diodes, you can make this distortion pedal have much more distortion and volume. You can pick up compatible replacement components online or at local electronics supply stores. You can even salvage a lot of great working components from old electronics that are no longer used such as computer speaker systems, old stereo equipment, etc. You’d be surprised how many working switches, knobs, capacitors, transistors, resistors and much more are being sent to the landfill everyday.
Another great option to get a kit which supplies all of the necessary components along with instructions on how to perform the mod. One popular DS-1 mod kid is the Fromel Boss DS-1 Distortion Supreme Mod Kit for DS1 which comes with enough components to give your old DS-1 completely new characteristics. The kit comes with vintage 1n34A germanium diodes along with high quality replacement capacitors. 
This kit gives the pedal a smooth and more intense distortion than the original. The following picture shows all the replacement parts that this kit comes with:
In order to perform the mod, you’ll need to have a working Boss DS-1 (the kit does not come with the pedal itself), a soldering iron, a screwdriver, side cutters and some type desolder (braid or vacuum type). The kit comes with step-by-step instructions. The basic idea is to dismantle the pedal and then work your way around the circuit board de-soldering old components and soldering in new components. This will probably take you anywhere from an hour to an entire afternoon depending on your experience level. Overall, it’s a great project for learning how to mod and build your own distortion pedals.
The kit is rather extreme in that it replaces almost all of the electronics components on the Boss DS-1’s circuit board. If you don’t want to replace all of the components, or just want to experiment with different mods, you can find replacement components and use them to mod your DS-1. If you don’t want to go the kit route, and decide to just gather up some replacement parts, Premier Guitar magazine has an excellent article on DS-1 Mods that has a great listing of potential replacement components. My favorite on the list is the Marshall JCM style mod which simply replaces 4 capacitors, 2 resistors and 2 diodes. Another good one from the same page is the vintage distortion mod which only requires replacement of four components but results in a much richer distorted tone. The components are commonly found online or at electronics supply stores such as Radio Shack. All four components should be in stock at most radio shacks for less than $10 total. This is a great project for a beginner pedal modder that wants to get a great sound out of a cheap pedal.
The Boss DS-1 is a great, cheap pedal that is easy to mod. You can purchase a kit such as the Boss DS-1 Distortion Supreme Mod Kit for DS1 which comes with all the necessary components along with easy-to-understand instructions or you can follow online guides such as Premier Guitar’s DS-1 Mod guide. Either way, modding the DS-1 has many options for different sounds, especially extra gain and volume, true bypass switching, led’s, extra controls and much more. Try doing something in stereo output for fun. You can introduce a second circuit for the right signal and leave the original DS-1 sound in the left for an almost double tracked sound. The possibilities for modding this pedal are endless and I am positive I will return to the subject of Boss DS-1 Mods on this website in the very near future.