#holyboxghost

Most people make them true bypass, then switch the diodes in them to something they favor, add a mid control, and/or make it more transparent. I usually want them to have a bit more gain and a mids control. I had a pretty cool TS9 for a while it was also painted black and had a yellow LED. I miss that. Bleh. 

Oh man, I love these kinds of questions. I’m actually writing a more in-depth article on diode-based pedals right now, so you’ve given me reason to finish it sooner. Anyway…

Circuits can be designed to “clip” off signal peaks, thus distorting the sound. The character of this distortion depends on the design of the circuit, namely, how suddenly the clip occurs and how soon different frequencies clip. Here’s a really bad picture depicting clipping from a pair of diodes:

Diodes are a circuit element with a number of interesting properties. Their defining characteristic is that they only allow current to flow in a single direction. This is due to the way current flows with a given voltage. We call this the I-V response. Resistors have a linear response to applied voltage (see Ohm’s Law), but for diodes the response looks like this:

By looking at this graph, you can see a few things. First, when a negative voltage is applied the diode is reverse biased, which means only a tiny amount of current can pass through (until it reaches breakdown, anyway). This gives the diode it’s one-way valve property. Second, you can see that the diode doesn’t do much until the voltage reaches Vf (the forward voltage), at which point the current blows up. This means that the signal is effectively clamped down at Vf when the diode is fully conducting. The forward voltage is the most important parameter to consider when you want to design a diode-clipping drive pedal, or swap diodes in an existing pedal. Higher voltage means more dynamic range before clipping, whereas a lower voltage will distort sooner. Vf can vary slightly with frequency too, lending different diodes their own tone. And every diode type has a slightly different “knee”, or the shape of the I-V curve near Vf, that determines how drastically the clipping can happen. 

Of course diodes aren’t the only way to achieve clipping—one could even argue that diode-based circuits were made to emulate “superior” forms of clipping. In a tube amp or in circuits with stacked transistors, we can get clipping by amplifying a signal beyond what the power supply is able to provide. For example, if you have a 1V signal entering a distortion pedal and want to amplify it by 20dB (100 times louder), the signal isn’t going to reach 100V. The pedal is powered at 9V, so any part of the signal that would go higher than that is clamped down. The resulting waveform is similar to what you get from diode clipping, where a pure sine wave has its top and bottom clipped off.

So why does this sound like distortion? When the amplitude of a waveform can’t go beyond a certain threshold, new frequencies are added which the human ear perceives as distortion. I can give a treatment of Fourier analysis but I think that’s a bit overkill. Basically all you need to know is that you can add higher order harmonics to a sine wave (red line) to produce a square wave (black line), as shown here:

So any waveform with a clipped off top like the diode clipping waveform is going to contain higher order harmonics because it’s similar to a square wave. The more clipping you get, the more it approaches a square wave and the more higher order harmonics you have, giving the distortion a buzzy, edgy tone. Less dramatic clipping gives you a smoother tone. 

We most often see two identical diodes back to back, which produces a symmetrical waveform. Symmetrical clipping produces more odd harmonics which have a harsher sound. But, if you swap a diode for one with a different Vf, then you’ll see an asymmetrical waveform. This asymmetrical waveform contains more even harmonics that sound more natural. (For what it’s worth, I like both). 

In the Longsword, I opted to use a pair of back-to-back LEDs. I like LEDs for clipping because their forward voltage is 1.7V, meaning you have more dynamic range before clipping. When they finally do clip it’s a more sudden onset which introduces makes them sound aggressive. In the Bastard Sword I used green LEDs (2.1V), a red LED paired with a 1n34a (germanium, 0.2-0.3V) for asymmetrical clipping, and a pair of D9Es which are weird Russian germanium diodes found in the Klon (purely for mojo fun). Although I should emphatically state that the op-amp itself is also clipping quite a bit and adds its own important character to the sound. 

16. Are you going out of town soon? NOPE I NEVER LEAVE!!!!!!! actually i’m going to rome but not until january. so still no.

D: a song that reminds me of a fictional character

Parents Just Don’t Understand (Leslie Knope)

F: a song that i’ve used as a ringtone at some point

submit a picture of dickbutt

Upstate blues by into it over it