FUZZ FACE: Output Level Mods

One of the most common complaints about a Fuzz Face is the low output level. For such a famous circuit, the usual output tricks do not seem to be especially well documented. The good news is that none of them requires changes to a standard layout.

The key thing to understand is that the usual Fuzz Face output is not taken straight from the collector of Q2. Instead, the output cap is connected to the junction of the 470Ω and 8.2k resistors.

A simple way to think about this is like a volume pot. Q2 generates signal across the full collector load, but the output is taken from partway along it, not from the end.  So the circuit is effectively turning its own signal down before it even reaches the output cap.

In stock form, the tap is very close to one end of that “pot”, so you only get a small fraction of the available signal. That is why the standard Fuzz Face output can feel lower than you might expect.

So the basic idea behind these mods is very simple: move the tap, or change the ratio, and you get more signal out — without necessarily changing the character of the fuzz itself.

FUZZ FACE MATH

Because the output is taken from the junction of the two resistors, the available output level is set by the ratio of the top resistor to the total collector load.

So the basic equation is:

Tap fraction = top resistor / total resistance

This is an idealised, unloaded ratio, but it lines up very well with what shows up in simulation.

Stock Fuzz Face

Top resistor = 470Ω

Total resistance = 8,670Ω

470 / 8670 = 0.0542

So the stock output tap sees about:

5.4% of the available collector-load signal

With 470Ω over 8.2k, the output only sees about 5.4% of the signal developed across the full 8.67k collector load.

So if the resistors were a pot - it would be turned 95% of the way down.

Standard 1k mod

If you change the 470Ω resistor to 1k, and leave the 8.2k alone:

Total resistance becomes:

1000 + 8200 = 9200Ω

Now the tap fraction is:

1000 / 9200 = 0.1087

So the output tap sees about:

10.9% of the available collector-load signal

That is almost exactly double the stock tapped output:

10.9 / 5.4 ≈ 2.0

This is why the standard 1k mod works so well. It is not magic, it just gives the output tap roughly twice as much signal to work with.   It does change the bias a little, but hey….   

Resistors swapped

Top resistor = 8200Ω

Total resistance = 8670Ω

8200 / 8670 = 0.9458

So now the output tap sees about:

94.6% of the available collector-load signal

Compared to stock, that is an increase by a factor of:

94.6 / 5.4 ≈ 17.5

So swapping the 470Ω and 8.2k resistors gives about 17.5 times the stock tapped output.

That is why it gets dramatically louder - this will be super hot, likely too hot for most.

Equal values

If the two resistors are balanced, say 4.3k and 4.3k, then:

4300 / 8600 = 0.5

So the output tap sees:

50% of the available collector-load signal

Compared to stock, that is:

50 / 5.4 ≈ 9.2

So an equal split gives about 9.2 times the stock tapped output, while still being much more controllable than the fully swapped version.   It’s still going to be very hot, but it can be quite cool for running the guitar volume wound back for sparkling clean tones, but still with a lot of level.  

Straight from Q2 collector

Not recommended - you are now taking the full available collector signal.   It’s a massive signal.  

So that is effectively:

100%

Compared to the stock tap at 5.4%, that is:

100 / 5.4 ≈ 18.4

So taking the output straight from the collector gives roughly 18.4 times the available stock tapped output.

This is the nuclear option in terms of output level.   

STOCK FUZZ FACE OUTPUT

Probably should start with a stock version as a reference.  Everything is set to full, and there's a healthy output level.  Happy days...  but not all Fuzz Face stories have happy endings, so read on.

200mv peak to peak in, about 430mv out

Here's the frequency response with the fuzz swept, which is how I'll do the rest of the comparisons.

And here's the standard schematic that we probably all know by now - note the voltages for comparison later.

R2 & R3 SWAPPED

A simple swap of R2 & R3 will increase levels quite dramatically - note the voltages compared to the stock schematic.

They look the same right - yes they do, but note the difference in scale on the voltages.  Now the output at the junction is a tad over 7 volts.   

The frequency response looks the same as the stock version

R2 & R3 MATCHED

This time the R2 & R3 values have been balanced - again, note the voltages compared to the stock schematic. 

Looks familiar right?

Now the voltage at the junction is about 3.5 volts - still very large, but only half of the method above.  But with a bit of experimenting or the use of trimmers, you can fine-tune this to a place that you're happy with.

I always like to question how much output a pedal really needs, as it seems to be a thing for modern pedals to have more output on tap than anyone would ever use.  Is all that unused gain just additional noise and a poor gain structure overall?

STRAIGHT FROM Q2

This is the nuclear option - this compares the stock output to straight off the collector.   It's massive by comparison.

So in conclusion - if you have low output Fuzz Face but really like the sound (which means you probably like the bias), maybe try one of these tricks before adding a trimmer, which will change the bias to Q2, and subsequently, the sound of the Fuzz Face.

This does completely ignore Q1, but this post was never intended to cover every possibility of the Fuzz Face.