I don’t normally give modules names as I think it’s kind of confusing, but while working on this module, a fitting name popped into my head and there it stuck. And from that moment on this module shall be called ‘the leech’.
The whole idea for this module came from a question on Reddit, or was it Facebook, don’t recall, doesn’t matter either. It was a question about a passive way to convert a gate to a trigger, not that the actual question has something to do with this module, but it sparked an idea in me to see how far I could push the concept of a passive module. What could one come up with if you couldn’t use a power supply. Silly, I know, but somehow the thought connected with the concept of a bridge rectifier and guitarists using almost empty batteries to power distortion pedals. These things formed a rough concept for a module I just had to try and build.
The idea was to use the incoming audio signal to power a fuzz effect by running it through a diode bridge. Since, at modular levels, audio signals are around 5V it should be possible to derive a usable voltage. A bridge rectifier will give me somewhere a voltage drop of, theoretically 1.2V to 1.4V as it passes through 2 diodes. Leaving me somewhere around 3.8V to work with. If the fuzz can be made to clip as near to its maximum voltage rail as possible I shouldn’t loose too much of the signal level. I’m guessing that at a 10vpp input signal I’m left with 6vPP on the output. Seems doable.
Now a fuzz is basically just 2 transistors boosting the signal to the point of clipping, in essence, a bad amplifier. The fuzz schematics you can find on the internet, like the fuzz-face, need some tweaking as they’re build for guitar level signals but circuit topography is pretty much the same. I didn’t use any fancy transistors, like is so often the case in a fuzz pedal. You can put in germanium transistors, which will certainly score you some hipster points, or solder some pin headers in instead of the transistors and try out a bunch of different combinations. Let me know if you find anything that’s particularly interesting.
The “fun” starts when the input signal isn’t a nice and constant waveform. The voltage generated by the bridge rectifier will change depending on the input level (and to a certain extend its frequency), which means the voltage powering the fuzz will be highly unstable. As a result, things will start to break down when the incoming signal starts to drop, cause all kind of havoc on the passing signal. But on the upside, it’s quiet when there is no signal coming through.
Needless to say, this module kind of really destroys everything that goes through it and isn’t that suitable for a ‘subtle’ crunch or saturation effect. But that might just be what you need on some occasions. It’s only 4HP.
Control wise, there is little to it. A single pot that allows you to control the effect of the capacitor that’s used to stabilise the generated voltage of the bridge rectifier (wow, that’s a whole mounth-full). It affects the way the bridge rectifier works, if turned left, the capacitor will smooth things out removing ripple from the signal, on the other side, well, it won’t. I use a 10uF for this, but you could put in a bigger or smaller one and see what that does. That’s pretty much it. There’s also a led, because it’s fancy. Turning the led on or off does change the characteristic of the fuzz a little bit, but not by much. If I do a second run of the module I will omit the switch as it is of little use.
- All diodes are 1N4148
- Switch common pins need to be 2 and 5