I was playing around in LT Spice Model of the famous Fuzz Face pedal circuit.
The circuit is brilliant in its simplicity. The first transistor in the signal path is biased as a high gain amplifier that feeds the base of a second transitor which provides a voltage feedback to the base of the first transistor. Note that the transistor model I used is suppose to be similar to those old germanium ones used back in the day. I can’t really vouch for these models though. I found them somewhere on a forum so the origin of the models are somewhat nebulous.
This is a pretty easy circuit to start with if you interested in putting together your own pedals. You can built this circuit youself in a few minutes with some old parts you may have laying around. If you don’t have these sort of parts laying around you will soon be able to buy them in the Electric Chili store.
Take a look at the output waveformbelow. It almost looks like I just generated a square wave. It has a solid pattern which is good musically. We don’t want anything that’s a hot mess because it’ll sound like crap.
Check out the FFT below. The blue sinewave is the simulated input. You can see that the input isn’t modeled as a perfect sinewave but that’s OK. We’re unlikely to get a perfect sinewave out of guitar. In face, if we did, we would hate the sound. It would be pretty darn annoying. The Blue wave is the output of the circuit. You can see that it sustains many of the high frequency signals. This makes sense because of the hard edges on the waveform.
The model is set up so we can see different pot settings can be evaluated at the same time. Pretty slick eh? Here’s a copy of the model itself so you can play around with it yourself. Change the resistor and cap values and take a look at how it affects the output. Throw a diode in a strange place to see how if affects the signal. A tool like this is a great way to learn about how analog circuits work so if you haven’t downloaded LT SPice, you should Google and get it!