Tonebender MKIII clone (Aion Electronics Phobos)

Here is my last build: a Tonebender MKIII clone! The tonebender was initially a derivative of the Fuzz Face, a bit closer to an amp distorsion than a fuzz. (read my post about the different types of fuzz) It became quickly famous thanks to a lot of guitarists like Jimmy Page or Jeff Beck.

The MK2 version used two germanium transistors to get fuzzy tones. However, due to the nature of the circuit, the quality of the fuzz was very dependent on the transistor's gain and characteristics, just like in the Fuzz Face. In order to avoid the selection of transistors, the Mk3 version used 3 transistors, so that the quality of the sound is less dependent on the germanium transistors used. Here is my version:

I used a small sticker that I bought in London representing a small power trio :) I used the same knobs used on the original MKIII, and the blue of the Park Fuzz

And of course, my laser-engraved logo :)

If you are interested, I am selling it for 165 euros (free shipping, unique piece)

 Buy

Inside, I used a Aion Electronic Phobos PCB. It is a very nice PCB (like most of the Aion Electronics PCBs!), with many options to turn it to a Baldwin-Burns Buzzaround, a Vox Tonebender MKIII, Park Fuzz Sound, or the Prescription Electronics Yard Box. Red and blue wiring to fit the color scheme.

I used 3 Telefunken AC116 germanium transistors. Their gain is perfect for this kind of build, and thay are slightly cheaper than AC128 transistors that are used for Fuzz Face guitar pedals. They also have quite a cool package, made to cool them easily.

How does it sound?

I made a quick video (not so good, sorry....)

Like Fuzz Faces, it sounds really good on an overdriven amp, and has a warm, bassy fuzz feeling. It also reacts well to the guitar volume knob.

If you are interested, I am selling it for 165 euros (free shipping, unique piece)

 Buy

How does it work?

Well, it is finally quite close to a Fuzz Face: a first stage amplifies the signal, which in returns makes the last transistor saturates: here is the fuzz! The main difference is that contrary to the Fuzz Face, the first stage is a 2 transistors amplification stage, and it amplifies the signal enough so you do not need a feedback loop to make it bigger.
Lets see that in details.

Here is the schematic of the Tonebender:

And as usual, the schematic divided in functional parts:

So, the first stage amplifies the signal, which then makes the Q3 transistor saturates. Then, there is the tone control stage to remove of bit of trebles and fizziness, and finally a volume output stage. Notice that the circuit is in reverse polarity because germanium PNP transistors are used here.
Lets analyse each par one by one!

The amplification stage

The signal goes through a first C1 coupling capacitor, to avoid any parasitic DC current to go in the circuit. R1 and R2 form a voltage divider to bias the first Q1 transistor.

You can notice that Q1 and Q2 are placed one after the other. This configuration is called the Darlington configuration, and it allows the signal to be amplified twice! Q1 amplifies it one time, and then Q2 re-amplifies the signal. Thus, you can get very high amount of amplification, and still use low gain germanium transistors! This avoids the very painful job of finding high gain germanium transistors like with the Fuzz Face. A hfe of 60 is enough for each of these transistor, which is a easy-to-find value for germanium transistors.

After this amplification stage, there is again a coupling capacitor (C2), and the Fuzz potentiometer allow to reduce the signal. When you turn the knob, the resistance of the potentiometer will increase and the signal will be "less amplified", and thus, you will get less saturation out of it.

The saturation stage

Now that the signal has been amplified a lot, it will hit the Q3 transistor and make it saturates, creating a beautiful fuzzy distortion that we love.

The germanium diode is used to prevent issues with rising temperatures. As you may now, germanium is temperature sensitive. When the temperature changes, the characteristics of the diodes change the same way the characteristics of the Q3 transistor, and avoid biasing problem by flowing the excessive current to ground. I am not sure of how it works precisely though so if you have more insights, I would be glad to hear it in the comment section!

Tone section

The tone section helps to remove a bit of the trebles of the Fuzz, and avoid it to sound too gritty. It is a very nice addition that give the fuzz a bit more versatility!

The tone section is composed of two low pass filter. One cuts all the frequencies below 7kHz (max trebles), and the other at 159Hz. The tone knob mixes these 2 filters. The more you go on the right, the more the 159Hz will be important and your sound will have less trebles.
It is a very simple layout that works quite well!

Output stage

Simple layout that we have already seen in the Fuzz Face circuit analysis.

A first resistor reduces the signal, and a 100kB pot sends more or less signal to ground, adjusting the final volume of the fuzz!


There it is! I hope that you liked it.
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To go further:

• History of Tonebenders by D*A*M stompboxes
• Tonebender timeline on the Big Muff page: very detailed historic of the Tonebender pedals
• Aion Electornics Phobos project page
• Fuzz central post about the Tonebender MK3