The Fuzz Face was released in the 1960s, but it is remains iconic. What is it in the fuzz pedal schematic that makes it unique?
It is basically a two transistor circuit, but a close look at the design reveals why it is very effective.
The Fuzz Face Circuit Layout
The Fuzz Face has two controls, three capacitors, four resistors and two transistors. The first transistor input goes in a DC capacitor.
It moves to the base, a single collector resistor and grounded emitter. The second transistor base is the driven load and is coupled directly.
The secondary transistor works as an emitter follower. The voltage emitter follows the collector of the first transistor.
This means that for the first transistor, the emitter transistor serves as feedback. It passes a current proportional to the voltage of the primary transistor on the base.
The Voltage Feedback
The voltage feedback (VF) comes with the properties necessary to get the best gain possible for the transistor. This is essential for a distortion device, and its impedance is low input.
Unlike other transistor hookups, it cannot do any hard saturation. If you drive this with a sizable signal, the voltage goes into the emitter.
What happens is the bias voltage is reduced via the biasing resistor. This reduces some of the input signal and you get mushy saturation, also essential for fuzz pedals.
Fuzz Faces have a bias for the first transistor’s collector, providing plenty of room. The input stage is going to strike the signal polarity.
Another notable thing is we have to note is the Fuzz Face has asymmetrical clipping.
The Second Transistor
The second transistor base is hooked onto the first transistor collector. The bias current is determined by the emitter resistor’s value, and with the classic Fuzz Face it is 1K pot.
The pot makes the static current go into the device. The end result is the static needs to be equivalent to the voltage of the first collector.
This computation however, subtracts the second transistor’s voltage at the base emitter. The figure is then divided by the current (1K).
The current goes into the collector resistance. The two collector resistors have voltage going through them.
The voltage is equivalent to the static current times of both. Since the first transistor biases near the ground, there is space for the second transistor for the emitter collector voltage.
The AC Collector Load
You can figure out the second stage gain by the AC load ratio within the collector. This is then measured relative to the AC emitter load.
The AC load collector is the totality of the collector resistors.
The AC emitter load is the part of the 1K pot that isn’t ground shorted via a capacitor.
What this means is the gain varies from low to high, from 8 up to the point when the pot is at the maximum setting.
Fuzz Face Models
The oldest Fuzz Face models were in dark or light grey and red. The logo was in black or white, and the text indicating the age of the pedal.
Arbiter-England is the oldest one and Dallas-Arbiter followed. Today, Dunlop makes several types of Fuzz Faces with different transistors.
The transistors make up the most sensitive components of the Fuzz Face. There are two types used:
- Silicon Transistors: high gain with a rather harsh sound
- Germanium Transistors: have a smoother, warmer sound
Germanium transistors have a more classic sound, closer to Hendrix than the silicon. The drawback is germanium transistors are not consistent, plus they are more sensitive to temperature.
Germanium transistors function similarly, but the sound they produce will vary. Some fuzz pedals use the AC128, while others rely on the NKT275 transistor.
Because the old germanium transistors are sensitive to temperature, manufacturers have opted for silicon transistors. Silicon transistors are more stable, and among the most popular are the BC239C, BC209C, BC183KA, BC183L etc.
If you’re going to buy a germanium transistor, make sure that it is of the highest quality. The type of transistor you choose will affect the performance.
Some germanium transistors’ gain value is inconsistent, and leakage current is possible.
The Fuzz Face circuit is a basic 2 stage amplifier. This is divided into the feedback network, the output stage and the input stage.
The feedback network has a direct effect on the other elements such as the frequency response, the output impedance, input impedance and voltage gain.
The Fuzz Face design was inspired by the Sola Sound ToneBender and the Maestro Fuzz Tone, but the Fuzz Face circuit is simpler with just a couple of transistors.
It isn’t clear just when the two transistor layout showed up however.
Layout and Design Notes
The classic Fuzz Face utilizes a single layer PCB. The board’s right side comes with pads where the cables are connected to the DPDT foot-switch, the potentiometers, jacks and battery clip.
A Common Emitter (Collector Follower) PNP amplifier is the input stage of the Fuzz Face. This gives it a low input impedance and high voltage gain.
You also get high output impedance. This is not the most ideal configuration, but it is simple and effective.
The Fuzz Face has a 2.2uF input capacitor, which gets rid of humming and safeguards the guitar and pedal against currents.
The 33KΩ R1 resistor on the other hand, configures the parameters, the collector current, bias points and the voltage gain.
The input impedance of the Fuzz Face is low, but this can be modified with a potentiometer. Also keep in mind the low impedance handles guitar pickup loads, and this is why they don’t respond if you set them following other pedals.
Given this fact, it is better to set the Fuzz Face first before the others in the chain.
The relatively simple layout and schematics of the Fuzz Face only goes to show that a fuzz pedal doesn’t need to be complicated to be effective.
Even with the simple arrangement, you will get optimum results when you play.
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