Fuzz Face, Tone Bender MK1.5, Magic 66 and the most germanium Fuzz circuit (ever)
- pppcfuzz
- Nov 3
- 4 min read
Today I will write about the origin of the Magic 66, which is based on one of the most famous circuits in the fuzz realm (rivaled only by the Big Muff). Many legendary guitarists became famous for using this type of circuit — people like Jimi Hendrix, Eric Johnson, David Gilmour, and Syd Barrett, just to name a few.
Origins and Story of the Tone Bender MK1.5 & Fuzz Face
The exact origin is still unclear. The designer could have been Dick Denney (who seems the most likely creator) or Gary Hurst (the designer and builder of the Tone Bender MKI).
What we do know for sure is that the Tone Bender MK1.5 first appeared in 1965 and remained on the market until at least May 1966.
Later in 1966, while Sola Sound was upgrading the circuit to the Tone Bender MKII, Arbiter began producing and selling the Fuzz Face.
The Fuzz Face became available in shops around November of that same year. It quickly turned into a best-seller, partly due to its round and distinctive enclosure, the option to buy it in different colors (the first models came in red, black, and silver hammered paint), and its affordability and wide availability — it could be found in almost any music shop in the UK and abroad. Many early units have resurfaced in places like Sweden and the United States.
Around 1968–1969, the circuit was slightly modified to accommodate NPN silicon transistors (initially BC183LA or BC183K, and later BC108C, BC130C, BC239C, and BC209C).
Production continued — with various mergers between Arbiter and other companies such as Dallas — until around 1974–1975, when manufacturing in the UK ceased. Production later moved to the United States, where the pedal is still built and sold today by Dunlop.
The Circuit: Similarities and differences.
Both circuits are essentially negative-feedback amplifier circuits with two transistors. In these two cases, they are almost identical — but in such a finicky circuit, even small changes can make a big difference in sound.
With this schematic, you’ll be able to spot the differences between both circuits:
As you can see, the Fuzz Face essentially runs a 33K resistor from the -9V supply to the collector of the first transistor, while the Tone Bender MK1.5 uses a 47K resistor. One effect of this change is that the collector of the second transistor in the MK1.5 sits at a higher voltage, while it is lower in the Fuzz Face.
I think the MK1.5’s short production run was due to this reason. The OC75 transistors used in the MK1.5 are, by nature, very leaky, and when this characteristic is combined with the hot collector of the second transistor, it causes the MK1.5 to become a gated mess at temperatures above 25ºC (77ºF). Not a pleasant gated mess like the MKI, but an almost completely silent gated mess.
The Fuzz Face, running a little cooler — even when using the NKT275, which is a medium-leakage transistor — performed much better during the summer months than the MK1.5.
Another change that affects the sound was the value of the volume potentiometer. The 470k potentiometer in the Fuzz Face allows much more bass frequencies to pass through the circuit than the 100k potentiometer in the MK1.5 (remember, the early MK1.5 units were built with the same 470k as the Fuzz Face).
This makes the Fuzz Face a great match for single-coil pickups, but not as well-suited for humbuckers, while the MK1.5 offers a tighter and less woolly fuzz.
And… the Magic 66?
Nice question! Well, the Magic 66 is my take on this classic circuit, allowing you to choose the voice you prefer between these two iconic fuzz pedals.
Obviously, after all these years of these circuits being built, rebuilt, analyzed, and discussed, I’ve added some modifications to make them more usable for modern players.
One is the Hotness knob, a bias control that lets you keep the fuzz working just the way you like it, even with significant temperature changes. The other is a Fuzz control that expands the fuzz range. Unlike the two vintage pedals, in the Magic 66 this isn’t an all-or-nothing control — it makes it easy to dial in the exact amount of fuzz you want.
A new change we added in the latest builds is an improved volume control. In this circuit, you can usually hear the treble concentrated in the last 10% of the potentiometer’s range (similar to the Fuzz control). I made some changes to the volume pot’s taper to expand this range.
Well… now you know more about this marvelous and beautiful circuit. But are there other fuzz pedals inspired by it? Yes — the Vox Tone Bender V828 (the Italian Tone Bender), the Schaller Fuzz, the Zonk II… but we’ll talk about those another day.
Resources: fuzzboxes.org
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