Since I started using only small (5 to 15 eatts) tube heads I relied only to simple boosters for dirt sounds: when the amp is always on the verge of breakup, and the amp and guitar combination is right, you don't need much more.
But recently, out of lazyness, I started going to rehearsals with just the guitar and a small pedalboard. At that point I felt the need to control a little bit the gain range and the tone because, in rentend rehearsals room, you have to adapt you tone to the random amps (mostly solid state, so forget tube crunch) you may find.
I don't have a rat right now (what a fool), I had a riot clone (nice!) but sold it since I didn't need it back then.... tried my old SD1 (C6 mod), but it was too middy, I did not bother diggin out the tube screamer (an old friend, but almost the same as the SD1); then had a cuople of old dod distortion boxes (the american metal is not too bad), but the AC jack annoys me.... The only pedal I had that I liked was an old boss DS2 turbo distortion (boost off).
Since I am a diyer I thought I could do something similar and proudly put it on my pedalboard.
Yes, it's a very generic overdive/distortion. But we always need something like this sooner or later.
I did it with just two transistors, some diodes, and little selection of components values; I succeeded avoiding the fuzz effect (always a risk wit bjt jobs) by using a very small input cap. The tone control is the wonderfully stupid tone control from Mark Hammer (tune it for you needs and thank Mark: great simple thing). The gain goes from cruncy and dynamic to distorted in a ds1 sort of way, with good bass response, and no mid bump; the tone range is really good from dark, but not muffled, to bright, but not too annoying.
The output of this small thing is surprisingly good: you always get a nice volume boost, if needed, even with the gain and the tone controls both at the lowes settings.
Note that the leds and diodes arrangement may seem strange but: a) it sounds very symmetrical to me, even if it looks very asymmetrical
b) they just give the right final touch to the sound: you will get distortion even without them, but it will be very edgy and a little bit fuzzy. c) if you don't experiment at least a little with clipping diodes you are not a true diyer 
but give at least a try to my idea.The transistors are BC549C, but anything with a hfe between 500 and 600 will work.
On the layout I added a reverse polarity protection diode that is not present on the schematic.