ElectroSmash Archive Pedals › You Can Build the Perfect Germanium Fuzz

You Can Build the Perfect Germanium Fuzz

The 1966 Dallas Arbitrer Fuzz Face has become the holy grail of Fuzz tones. It enjoys the most enduring reputation probably due to Jimi Hendrix use and abuse of this pedal. But not all the Fuzz Faces sound the same, in the old days, players sorted through dozens of pedals at a time to find the best sounding fuzz of the store. Why is that? 

In this project, we are going to build the perfect Fuzz with all the knowledge and experience that we have nowadays while keeping the tweaks and old character that make this vintage pedal to sound warm, round, and harmonically pleasant.

The FF circuit is rather simple: 4 resistors, 3 caps, and 2 transistors. Seems like pretty simple stuff, and in principle it is, but there is plenty of black magic and mystery associated with a good sounding Fuzz circuit, and it takes a lot of effort to get the things sounding just right.

The gain (Hfe) and leakage current inconsistency of the germanium transistors (the sound signature of this pedal) and the lack of ability/will to use the right components could make a huge impact on the tonal heart. The circuit layout in a pedal with a huge gain like this is critical and the component selection will leave its footprint on the sound.

The ElectroSmash Germanium Fuzz Pedal:

Compiling all the knowledge and experience that we have nowadays about the Fuzz Face, we have designed this project that tries to bring the good old classic fuzz tone using modern and controlled technologies:

germanium fuzz by electrosmash

Specifications:

The circuit schematic and Bill of Materials are available and open to modifications.

The Circuit:

The circuit follows the original Fuzz Face (positive ground) signal path design:

Germanium Fuzz Face Schematic

The pedal uses a double PNP transistor stage and a feedback network. The only two differences with the original circuit are:

We ensure that the signal path is the same as in the 1966 FF vintage pedal. All the other features (true bypass, LED, quality components, polarity protection, turrets, power supply capacitor, etc) will not change the sound of it and enhance the quality and performance of the pedal.

If you want to know all the details about the circuit, have a look at the Fuzz Face Analysis.

germanium fuzz face

Measurements:

The Germanium Fuzz total voltage gain is around 48dB matching the simulation. The pedal response has a low-frequency roll-off around 50Hz due to the two high-pass filters created by C1 and the Input Impedance and the combination of C3&RV2. There isn't any low pass filter in the circuit: in the treble side of the frequency response, the line extends flat to the limits of the measuring system. Not attenuating the high-freqs makes this pedal so rich harmonically, in the left image you can see all this harmonics when the pedal clips.   

germanium fuzz clipping

Time Response:

In the image below you can check how the Germanium Fuzz reacts to a sinusoidal input signal. It's interesting to see how the asymmetrical happens hapens first to the positive semicycle of the signal and how extremely distorted can get the fuzz output signal.  

germanium fuzz time response

note: In the beginning is difficult to apreciate the change in the input signal because the level is so low that the oscilloscope cannot capture the amplitude change.

The Documentation:

We have created simple manuals to build this project:

We also have a YouTube video that guides you during the whole building process:

Buying the Germanium Fuzz Pedal online:

You can use our online shop to get:

The Design Details:

Note: The original fuzz uses carbon-zinc battery (not modern alkaline) and it is claimed to give a better sound performance.

However, in order to reduce any excess of unwanted noise, two optional 100pF Miller capacitors (Cx) from base-to-collector on both transistors could be placed. This caps will limit the high-frequency response of the pedal and keep under control the hissing noise.

 jimi hendrix fuzz face

Germanium Transistor Selection - Biasing the Fuzz Face:

It is crucial to select the right transistors in order to archive the best sounding box. Germanium transistors tend to have high leakage current and an inconsistent gain value (Hfe). After years of experimentation and listening, it is agreed that the best match uses a low gain in the first stage (Hfe=80 approx.) and a high gain in the second stage (Hfe=120 approx.). Why is this? well if you use this values, the circuit bias points will look like this:

fuzz face bias

On the left image, the most important bias points are VC1=-0.5 to -0.7v and VC2=-4.5V, these values make the effect to sound fantastic. Using a Q1 and Q2 with the gains specified on the left image, the circuit will be biased to that points.

As we mentioned before, theses perfect AC128 120/80 Hfe transistors were long time discontinued. There is no source for them anymore and the only solution for builders is to pay astronomical prices for NOS, to buy big batches of similar transistors and try to find if it any left that meets the requirements, and try to avoid the re-labeled, fakes in that journey.

Instead of using the perfect and difficult-to-find transistors to get the circuit biased right, we can use almost any high-gain germanium PNP transistor (Hfe>50) and with the help of 2 trimmer resistors get the circuit perfect biased (right image). By doing this, we will create the same conditions for the transistors as if they were the perfect ones. Dunlop discovers this fact later on and includes a trimmer on VC2 in order to adjust it to -4.5V.

The Fuzz Face Transistors:

The first FF's manufactured in the UK used the AC128, a 45-165 Hfe European germanium PNP transistor, cheap/common at that time (later on replaced by the Newmarket NKT275). After this early germanium years, the production switched to the modern, temperature independent, and more stable silicon transistors like the BC108C, BC109C, and BC209C.

russian germanium transistors

The classic 60's/70's soft distortion Fuzz Face pedals (the ones used by Jimi Hendrix) used germanium transistors, but all the parts mentioned above (AC128, NKT275, SFT363E) were a long time ago discontinued. There is no official source of transistors for this pedal anymore, the only way to obtain this parts is using specific online suppliers (Smallbear, etc), eBay, Amazon, repair shops, and surplus outlets.

Russian Germanium Transistors: For this project, we are going to use Germanium PNP transistors. They were manufactured back in the old USSR Soviet days, they are under military specifications that make them good, with a consistent gain and not leaky in current.

Other 1966 Original Electronic Components Peculiarities: 

The parts used back in the 60s keep part of the character of the pedal, these are the most important facts: 

original fuzz face pcb

 Thanks for reading, all feedback is appreciated This email address is being protected from spambots. You need JavaScript enabled to view it.