Yet Another Fuzz Face
Do we need another fuzz face derivative? The answer is a resounding NO unless there is something new to be offered that gives this tired old device some new life.
One of the problems with the fuzzface circuit is that the best sound comes from germanium transistors, which are difficult to find, often leaky and vary in character with temperature changes. No doubt that the sweetest sound comes from Ge devices but these limitations can be difficult to overcome, especially for a bginning builder. A simple solution is to use silicon transistors but there is unanimous belief that Si devices make for a much harsher sound.
The Fuxx Face was my original attempt to produce a fuzzface clone with silicon transistors that had a solid but more flexible tone, and it has served well in that capacity. In the 6 or 7 years since I published that design I've come up with a variation that is closer to the original fuzz but has smooth distortion charactersistics.
One problem with silicon transistors is that the gain is typically much too high for the best sound in a fuzzface. I measured a bag full of 2N3904 transistors and the minimum hfe was 250. Other silicon NPN transistors that I had on hand measured even higher. Gain of 85 to 120 is thought to produce the best sound in this circuit.
A quick search of my sources turned up the MPS2369, which has a minimum hfe specification of 85. I bought a dozen from radioshack.com and they measured in the range of 110 to 120 for gain - perfect for fuzzface use. The MPS2369 is sometimes called a 2N2369 or PN2369. Merely substituting this transistor instead of the usual 2N3904, 2N5088 or BC108 will make an big improvement in tone. There are numerous other silicon transistors with similar gain specification that will be suitable for this circuit.
I decided to take the idea one step further for the YAFF, and changed the basic circuit slightly to add a couple of resistors, R7 and R8. The 100 ohm R7 resistor induces some local feedback into Q1 which reduces the gain. R8 has the same effect of Q2. By using a small amount of degenerative feedback, the gain is lowered and the response of the circuit is more useful for milder distortion effects.
Note that the value of R3 has been changed from the original fuzzface to set the bias at the collector of Q2 at 4.5v. It may be necessary to tweak the value of this resistor slightly to get the bias perfect, though any voltage on the collector from 4v to 5v will be acceptable. On the first prototype, R3 was reduced to 5.9k to get exactly 4.5 of the Q2 collector for testing purposes.
What does it sound like? I had a shootout with an original 1972 Fuzzface that contains BC108 transistors and the YAFF clearly was the better sounding effect. Its only drawback was that gain and fuzz was not as extreme at the max setting of the Fuzz pot. The YAFF was smoother with a tone more like a Ge version and with a good range of settings available. Build "Yet Another Fuzz Face" and give a whole new sound to your clone tone.
The parts layout and pcb have now been added. The capacitor C4 is not on the schematic and was included to provide extra filtering if an external power supply is used. Any value from 22uF to 470uF is fine. On the input, pads are provided for a 1M pull-down resistor to prevent pops when the footswitch is toggled. The pads labeled A and B are merely an alternate output to the volume control.
If jumpers are used for R7 amd R8, this board can be used to make a standard fuzzface.
Download the YAFF PCB and Parts Layout
©2002 Jack Orman This page last modified on Sunday, 14-May-2006 06:52:50 PDT
45676 hits since May 18, 2006
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©2002 Jack Orman
This page last modified on Sunday, 14-May-2006 06:52:50 PDT
45676 hits since May 18, 2006