PHOBOS GERMANIUM FUZZ 1

PROJECT NAME

PHOBOS

BASED ON

EFFECT TYPE

PROJECT SUMMARY

DOCUMENT VERSION

Tone Bender Mk. III (3-knob)

A reproduction of the third version of the Tone Bender germanium fuzz sold by Macaris in London in the

late 1960s.

BUILD DIFFICULTY

IMPORTANT NOTE

PHOBOS GERMANIUM FUZZ 2

1 Project Overview 8 Drill Template

2 Introduction & Usage 9 Enclosure Layout

3-4 Parts List 10 Wiring Diagram

5-6 Build Notes 11 Licensing

7 Schematic 11 Document Revisions

The Phobos Germanium Fuzz is a clone of the Colorsound / Sola Sound Tone Bender Mk III. While the

first version was essentially the same topology as a Fuzz Face, and the second version added a gain stage

contemporary clone. The Elka Dizzytone and the Prescription Electronics Yard Box were two others.

Aside from the Buzzaround, all of the rest of these variations can be build on this PCB.

A note about the name: the original Colorsound / Sola Sound unit was not called the “Mark III”, but the

Vox-licensed version was. As a result, this circuit is commonly called both the “Mark III” and the “three-

knob” Tone Bender. This project will refer to it as the Mk III to differentiate it from the Mk II, which is

available as another project called the Deimos.

The Phobos project has a voltage inverter which allows you to power the effect with a standard center-

negative adapter while maintaining the positive-ground operation of the original. The PCB also includes

biasing trim pots so you can dial in a perfect bias without having to swap out resistors.

PHOBOS GERMANIUM FUZZ 3

This parts list is also available in a spreadsheet format which can be imported directly into Mouser for

easy parts ordering. Mouser doesn’t carry all the parts—notably potentiometers—so the second tab lists

all the non-Mouser parts as well as sources for each.

View parts list spreadsheet →

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PHOBOS GERMANIUM FUZZ 5

For this circuit, as with many other vintage fuzzes, it’s not so much the part number of the germanium

transistor as it is the properties—specifically, gain (hFE) and leakage.

The Tone Bender Mk III is less finicky about transistors than the Mk II, but still moreso than other

germanium circuits like the Fuzz Face or Rangemaster. You can save a lot of time by just buying a

• Q2: hFE 50-100, low leakage (<100μA)

• Q3: hFE 90-120, medium leakage (100-300μA)

The characteristics of Q1 and Q2 are less important than Q3 due to their Darlington configuration. In

fact, many people have even used low-gain silicons for Q1/2 with no reported change in tone, since this

stage just boosts the signal and all the actual fuzz comes from overloading Q3.

Biasing

As a starting point, set the two bias trimmers to around 9:00 (approximately 10k total resistance when

combined with R3 and R7). Then, with a multimeter, touch the black and red leads to the pads marked

“Q1/2 TEST”, which is the shared collector of Q1/2. Rotate the trimmer until the multimeter reads -3.5V.

This voltage may be positive if the test leads are reversed, but what’s important is the absolute value.

best when the bass is cut back slightly.

Then, with the black lead touching ground, touch each leg of each of the transistors and see how they

line up with these target voltages.

• Q1: Collector -3.5V, Base -1.5V, Emitter -1.4V

• Q2: Collector -3.5V, Base -1.5V, Emitter -1.4V

• Q3: Collector -2V to -4V, Base -0.05V, Emitter 0V

The collector voltages are just a baseline. For Q1/2, anything from 3V to 7V will work fine and will sound

roughly the same. For Q3, the EQ does change a bit depending on the bias, but as long as the transistors

have the right characteristics, the overall character of the fuzz will be the same across the range.

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There were a number of other variants of Mk III that each had minor changes. Start with the original

This is also identical to the Park Fuzz Sound (3-knob version), except the Park uses 2n2 for C6.

Park Fuzz Sound (2-knob)

• R1: 100k

• R2: 680k

• R10: 470k

• C2: 200pF

• C4: 25uF (nearest standard value today is 22uF)

The 2-knob version omits the Fuzz control and hardwires it full-on all the time. If you’re building this

variant, it’s recommended to keep the Fuzz control in place. If it’s turned all the way up, the unit is stock,

but this way you still have the option to turn it down.

volume mod in the next section.

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Cut out this drill template, fold the edges and tape it to the enclosure. Before drilling, it’s recommended

to first use a center punch for each of the holes to help guide the drill bit.

Ensure that this template is printed at 100% or “Actual Size”. You can double-check this by measuring

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Enclosure is shown without jacks. See next page for jack layout and wiring.