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Understanding Silicon and Germanium Clipping Diodes


by Andrew Tycksen

In the world of electric guitar tone where everything seems to be drowning in buzz words whose meanings are basically arbitrary—creamy, warm, snappy, wooly, and bright, just to name a few—it can seem nearly impossible to discern what actually differentiates the pedals we end up choosing to use from the ones we leave on the shelf.  One thing we get asked a lot here at Lunar is the difference between germanium and silicon clipping diodes (not to be confused with transistors).  I’m going to do my best to help clear the air surrounding this overwhelming question.

DISCLAIMER: I am not a chemist or an electronic engineer; I’m a guy who likes guitar pedals.  I’ll do my best to get this information correct, but you’ll have to forgive my exchange of guitar jargon for technical terms.

We can’t talk about clipping diodes without understanding what clipping is.  Essentially, a clipping diode in the circuit of a dirt pedal sends the top of the waveform to ground, “clipping” off the peaks and causing the sound that we perceive as a “distortion” of our guitar’s clean signal.  Hard clipping, famously in the likes of the DOD 250, MXR Distortion +, ProCo Rat, and even the elusive Klon Centaur, is when this happens in the output section of the circuit.  Soft clipping is when the clipping diode is placed in the feedback loop of a dual op-amp.  This allows some of your guitar’s signal to pass through to the output untouched, as in the Boss OD-1 and BD-2, AnalogMan King of Tone, Marshall Bluesbreaker, and the Ibanez Tube Screamer.

Germanium and silicon are both semiconducting metalloid elements, which basically means that they have to be combined with another element (called a dopant) and heated in order to allow current to flow through.  The primary difference between the two elements is how much voltage each one needs to start working—germanium and about 0.3 volts and silicon at about 0.7 volts.

In the world of tones and what you actually hear, a germanium clipping overdrive will tend to have more high harmonics, as the high frequencies will turn the diode on at its clip point before the low frequencies will.  Silicon clipping may sound like it clips a bit harder than germanium because it responds faster than germanium when it reaches the clipping voltage, both turning on and off faster than a germanium clipping diode.  Silicon will also tend to have a more linear frequency response, resulting in some more odd-order harmonics.  It’s important to note that since all of this has to do with when the clipping point of the diodes are tipped, differences will be more apparent at low gain, whereas at high gain the differences will be more in feel than overall tone.

As you start scanning the market for what you think might be the best option for your rig, keep some of these options in mind:

Silicon Clipping

IBANEZ TUBE SCREAMER

Love it or hate it, everybody knows it.  You may have even owned one or two or five in your time spent spinning around the sun.  There are so many circuit clones, copies, and “modified inspired-bys” on the market, you hardly have to put in any effort to run into one.  Some of our favorite modern takes at Lunar are the Walrus Audio Warhorn, Keeley Electronics Red Dirt, and the JHS Bonsai.

 

DOD 250

Much more of a cult classic as far as overdrives go, the DOD 250 is around more than you might realize.  This pedal is loved for its magical low-end characteristics, and it stands out from many other famous overdrives because of its flatter frequency response.  If this kind of thing interests you, check out the Pelican Noiseworks 50/50, Greer Amps Vintage O.D. 390 Preamp, and the Earthquaker Devices Gray Channel (fun experiment: the green side of the Gray Channel has both silicon and germanium clipping diodes you can switch between).


Germanium Clipping

KLON CENTAUR

We all know the hype, but sometimes hype is justified.  Most Centaur users really like to set theirs as a clean boost to push the front end of their amp and just leave them on, but many also claim that this germanium hard clipping beast sounds amazing at higher gain settings.  If you can afford one, we recommend that you pick one up and try it yourself.  If you can’t afford one, try one of these amazing modern takes: Klon KTR, Foxpedal Kingdom, Ceriatone Centura, Walrus Audio Voyager, Wampler Tumnus, and even the Electro Harmonix Soul Food.

 

When all is said and done, it’s important to remember not to get hung up on these little details because there are exceptions to everything.  Just try lots of things in your rig and hold on to what you like.  In the words of my favorite guitar gear nerd, Duke Ellington, “If it sounds good, it IS good.”