This is one of the hundreds of pedals built around the JRC4558 operational amp chip and its variants. It has been built from 1977 to 1985. There are 2 controls: “Level” and “Over Drive”. Moreover, there are at least 5 versions of the circuit board: the first versions probably didn’t even use the JRC4558. This pedal isn’t particularly rare, even considering that has been out of production for more than 20 years, however it has a lot of fans. It has a pretty good sound when used to crank up a Marshall tube head, however may not sound so good with other amps. Building quality is standard Boss, which means they are built like a small tank. This was one of the first pedals to use FET switching instead of “True Bypass” switching: however I’m not sure if this can be considered as an improvement 
. The fact that 30 years later some pedals are still made in this kind of box means that the overall design was really good (compact size, easy battery access, anti-skid panels on top and bottom).
Specifications:
- Input Impedance: 220 kOhm
- Output Impedance: Over 600 Ohm
- Signal/Noise Ratio: 80 dB
- Current Draw: 3.5 mA
Samples coming real soon
Resources:
OD-1 schematics and nice images – on fffworks site (text is in Japanese language)
OD-1 Schematics at Schematic Heaven: OD-1 schematics
Short description on Boss USA site
And some videos from YouTube: