Distortion pedals and overdrive effects usually have a bunch of lovely transistors or op-amps inside and lots of knobs and dials to tweak the sound to your personal taste. However, it’s possible to get some crunchiness in your audio signal without all that fuss, as [Simon Hutchinson] demonstrates with his $2 “analog saturation box”.
The effect is achieved quite simply by installing a pair of diodes in opposite orientations, connected from the signal path to ground. This configuration is also known as wiring diodes in “anti-parallel.” When the signal increases in amplitude beyond the diode’s forward voltage, the diode conducts and the signal’s peak is clipped off, which creates a distorted tone. Since there are two diodes, one in each orientation, both the tops and bottoms of the AC audio signal are clipped in this manner.
The amount of clipping is highly dependent on the diodes chosen and the strength of the signal you’re working with. Silicon diodes clip around 0.7 V, while germanium diodes clip at about 0.3 V, but that doesn’t give you much flexibility. You can work with this to some degree, though. You can up the minimum clipping level by stacking more diodes in series in each direction, or you can put in a potentiometer to vary your signal’s level before it hits the diodes. Really, though, this hard voltage limit is why more commonly, we use active distortion or overdrive effects that have more options for gain and level and such.
[Simon Hutchinson] does an able job of explaining the effect and demonstrates its use with some simple beats. As a passive device, it’s pretty one note—there’s no EQs to mess with the frequency response, and no ability to change anything else about the sound, either. Still, it’s interesting to hear the effect it does have on a signal, and you might just find this is all the distortion you need. If you’d rather go into full-fat distortion though, we’ve covered that too.
When considering signal dynamics, hard clippers (often utilizing anti-parallel diodes as in this example) can significantly limit the dynamic range. It might be wise to incorporate a low-frequency filter beforehand to help preserve higher-frequency content, ensuring that the nuances of your audio remain intact. The hard clipping can erase high frequency content that’s riding on the back of lower frequency content.
Mixing in the hard clipper with the original signal can help to reduce both of those too – It’s about finding what sounds most appealing for your art.
My video showing the difference in guitar sound between different diodes
https://youtu.be/jlSrWHdPxg0
Thanks!
You can also use different kinds of leds in place of diodes to change your flavor of distortion.
It might be possible to make the circuit adjustable using LEDs or photodiodes and shining light into them at different levels
I built a synth module around this once. I had an adjustable pre-amp and post-amp so I could adjust the clipping level, pots in series with the diodes so I could add more skew, a DC-blocking cap on the output to un-bias the output if the pots were unbalanced, and lastly it fed through an adjustable low-pass filter so I could optionally round off the corners of the clipping.
It was really nice effect for sampled sounds and vocals.