As a cash strapped electric guitar playing teenager, one of my hobbies was making effects pedals. Many of them were made from plans in those cheap paperbacks that you could buy in the high street electronics shop Maplin. In the age of buying almost everything online, it seems almost absurd now that there were such shops, but I digress. Anyway the paperbacks in question (invariably penned by the prolific R.A. Penfold) contained all sorts of weird and wonderful gizmos, many of which I took a crack at, but the only device that I really needed and have hung on to, is this distortion pedal.
I genuinely can’t remember where I got the design for this one, it could well have been one of the aforementioned books, or on the other hand it might have been one of the many reverse engineered schematics available on a nascent internet. I reckon such reverse engineering was fair game to an extent given the markup on the things. Anyway, it doesn’t really matter, they all basically operate under the same principle, that being to configure an op-amp with a large gain in order to make it clip, but in the feedback loop put two reverse biased diodes that have the effect of reducing the strength of the clipping, mimicking the effects of over-driven tube amplifiers. My pedal had modifications so that three different types of diode could be switched into the feedback loop, each giving a slightly different characteristic to the distortion.
