Why you want silicon transistors
in your effect

The truth vs. the myth

Oh, no! Another crystal cult! Since germanium devices are obsolete and hard to find, a "germanium cult" has developed. For the unwary, germanium devices now assume a mythological aura of tonal majesty. ("Groovy! Like, crystals, man! Like power from the lost island of Germanis!") This fantasy has produced a demand for the inferior germanium parts.

The only good reason for using germanium parts is this: You want a museum-like reproduction of the original circuit. Before you start, though, consider this: At a premium price, you'll achieve a high-maintenance, unreliable effect. That's why even Dallas Arbiter, inventor of the Fuzz Face, switched to silicon. Besides, the stock of original parts is gone. Ever see an SFT363E transistor? Just imagine trying to find a replacement part while you're on tour.

Time to clear the air. Here's the truth. The only differences between silicon and germanium are these...

• Silicon devices turn on at 0.7 volt. Germanium devices require only 0.3 volt DC. So what? Either way, this is a fuzzbox. Give it enough signal to work with, and it clips.

• Give the box a little less signal, and it clips less. For some, clipping less is a more desirable effect. But to clip less, you don't need a germanium device. Instead, you need to adjust the controls (or the circuit). Our troubleshooting and mods section gives hints on how to adjust the circuit.

• Germanium devices often have less gain than silicon devices do. For small-signal devices, the gain difference can be three to 10 times. In a fuzzbox, more gain means more clipping. For this reason, some players think that a silicon device provides too much fuzz and sounds harsh. Guitar legend Jimi Hendrix, who used a silicon fuzzbox, disagreed. Anyway, the problem isn't the device type. The problem is the amount of gain. By hand-picking low-gain silicon transistors, we've solved the problem. Remember, our gain is "in the ballpark."

• Germanium devices are more prone to heat-based instability than silicon devices are. Sometimes germanium transistors shut down during a performance. (Here, "shutting down" probably means that Q1 turns on all the way and saturates. That event would cause Q2 to cut off.) Incidentally, shutting down isn't the only problem. In this old circuit, thermal runaway is a real possibility. Thermal runaway can destroy your transistors. Here, silicon devices have a slight advantage. Unfortunately even silicon bipolar devices are vulnerable to thermal runaway. Thermal runaway is a regenerative condition. As current flow increases, device gain or beta also increases. But as beta increases, so does current through the device. Runaway is one reason why conservative amplifier designs include negative feedback. If the prospect of runaway bothers you, switch to a JFET circuit.

• Germanium devices are much leakier than silicon devices are. Leakage alone can turn on a germanium device, causing a spurious signal. This signal isn't an "advantage." It's noise! Again, we're ahead with silicon, just as Jimi Hendrix was with his original, Dallas Arbiter fuzzbox.

• Low gain isn't always an advantage, even in a fuzzbox. Gain and sensitivity are related. Typical germanium devices are less sensitive than are typical silicon devices. The low sensitivity means that the device tends to load the input. To drive the effect, the input must produce extra power.

• Advantages

• Depend on silicon

• Parts

• Equivalent parts

• Where to find parts

• Low-gain transistors

• Assembly tips

• Build the circuit board

• Build the case

• Test the effect

• Troubleshooting & Mods

• For softer fuzz, add a stabilizer

• Why you want silicon transistors

• Schematic: Fuzzbox

• Schematic: Switch wiring

• Schematic: More bass

• Schematic: Reduced, sweeter fuzz

Copyright © 2009 by James T. Hawes. All rights reserved.

•URL: http://www.hawestv.com/amp_projects/fuzzbox/fuzz5.htm •Webmaster: James T. Hawes
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