Originally it was simply the fact that their guitarist (then only) Roehrenverstaerker extremely wide turning up and thus overloaded. This gives the Overdrive tone depending on the severity of a singing, screaming or screeching sound brutal, but has used the match quite an interesting dimension.
Electrically usually pretty easy to build, there are a number of possibilities to create this effect. Here are some links with schematics
Here you will find Schematic Circuit Diagram for DIY and further information on Distortion
|Distortion with Operationsverstaerker unf diodes||www.rabbathrecordings.com/Distortion.html|
|Various collection Fuzz / Overdrive / Distortion schematics||hem.passagen.se/robin2/effects.htm|
|Various distortion approaches||users.chariot.net.au/~gmarts/ampovdrv.htm|