Starting a Fuzz Face

[Mcentee2]

In the new year I want to build my own "perfect" fuzz face, I am tired of buying full pedals from boutique builder that just don't have quite what I am looking for.

In may be cheaper to set up a bread board and just audition countless components.

Certainly more fun, anyway!

So, the question is:

Is there a "right" or more accepted approach to this, in terms of:

1) keep all components exactly as a traditional build (33k, 470, 8.2k, 100k, and caps) and audition transistors until chancing upon a great pair ?

Or

2) tweak all necessary resistors depending on what transistors behave like? If this, then how tweakable can these be before it's no longer a"fuzz face" ie bleeding into tonebender 1.5 territory or other?

Or

3) only tweak say the the 8.2k to get bias right.


I know either of the above is possible, but one may be a more common and accepted fuzz face process!


At the end of getting a great Fuzz face together, I may go through and add input cap blends, or output cap tweaks on top.

Answers to this will inform my shopping list shortly!

Thanks

[tubelectron]

Hi Mcentee2,

Here is what I did some years ago - built from a Cornell-Arbiter Fuzz-Face casing :






The schematic is below and "vintage-correct" as far as possible with the values - sorry, the comments are in French  :



A+!

[Mcentee2]

Great, looks like you stayed with the original component values and chose transistors that worked😀

That is very nicely laid out, drawn and written, almost a wp knof serving itself!

[shredgd]

If you want the "perfect" FF, and you're using a breadboard, that's certainly a good start!

As germanium transistors are both difficult to find in the right working conditions (low leakage, gain matching) and to work with (leakage increases and bias voltage changes even if you simply touch the transistor), I suggest you to choose silicon.
My other suggestions are:
- try a 1uF for the input cap (the AnalogMan value): it removes a bit of the low end so the mids will shine through better
- choose a BC108A for Q1 and a BC108B for Q2. The current production ones sound incredible and you'll probably come back to this thread and thank me once you'll hear them
- use a regular pot (10k linear) in series with a 3.3k resistor to bias the Q2 collector, and start from half the power supply voltage (4.5v usually). Make little variations from there to hear how it affects the tone. For example I prefer just a little higher than that.
- experiment with a 100pF cap from base to collector at Q2 (alla Fulltone 70), even though the difference is so minimal it is difficult to hear.
- *most importantly*: if you use a buffered pedal after it, add a 560pF cap from output (central lug of the 500kA volume pot) to ground, or make it switchable: this will simulate a 5m cable capacitance from pedal to amp forming a low-pass filter with the volume pot, and will avoid the harshness you get from the buffer (yes, fuzz faces sound bad not only with a buffer in front, but also after them, unless you do this trick)
- everything else can be left stock, but someone raves about having a series resistance at the input of the pedal (a 50k linear pot is usually used) to emulate a slight reduction of the guitar volume pot, without the need to always search for that sweet spot on the guitar.

Have fun!

Giulio

[Mcentee2]

If you want the "perfect" FF, and you're using a breadboard, that's certainly a good start!

As germanium transistors are both difficult to find in the right working conditions (low leakage, gain matching) and to work with (leakage increases and bias voltage changes even if you simply touch the transistor), I suggest you to choose silicon.
My other suggestions are:
- try a 1uF for the input cap (the AnalogMan value): it removes a bit of the low end so the mids will shine through better
- choose a BC108A for Q1 and a BC108B for Q2. The current production ones sound incredible and you'll probably come back to this thread and thank me once you'll hear them
- use a regular pot (10k linear) in series with a 3.3k resistor to bias the Q2 collector, and start from half the power supply voltage (4.5v usually). Make little variations from there to hear how it affects the tone. For example I prefer just a little higher than that.
- experiment with a 100pF cap from base to collector at Q2 (alla Fulltone 70), even though the difference is so minimal it is difficult to hear.
- *most importantly*: if you use a buffered pedal after it, add a 560pF cap from output (central lug of the 500kA volume pot) to ground, or make it switchable: this will simulate a 5m cable capacitance from pedal to amp forming a low-pass filter with the volume pot, and will avoid the harshness you get from the buffer (yes, fuzz faces sound bad not only with a buffer in front, but also after them, unless you do this trick)
- everything else can be left stock, but someone raves about having a series resistance at the input of the pedal (a 50k linear pot is usually used) to emulate a slight reduction of the guitar volume pot, without the need to always search for that sweet spot on the guitar.

Have fun!

Giulio

Thankyou great tips as well as the general approach to use stock values and really just tweak q2 collector resistor to bias and get the right transistors😀 that work for that.

Great advice, thanks again, it makes the breadboarding so much easier.

[Electric Warrior]

A Fuzz Face shouldn't require all that much tweaking. Transistors with a reasonable gain/leakage will bias alright. There is a wide range of voltages that will be good.

If the bias is off, you may simply tweak Q1's collector resistor as the voltages on both collectors depend mostly on Q1's leakage and gain. If you tweak this one, the relationship between the voltages on Q1 and Q2 should be correct for a Fuzz Face.

The rest is down to auditioning transistors and selecting a pair that works well for you. Buying a handful of transistors of the same type should give you a wide enough range of gains to work with.

The MK1.5 is biased only slightly hotter than the Fuzz Face. Some of the "colder" MK1.5s are biased just like a "hot" Fuzz Face.

[Mcentee2]

A Fuzz Face shouldn't require all that much tweaking. Transistors with a reasonable gain/leakage will bias alright. There is a wide range of voltages that will be good.

If the bias is off, you may simply tweak Q1's collector resistor as the voltages on both collectors depend mostly on Q1's leakage and gain. If you tweak this one, the relationship between the voltages on Q1 and Q2 should be correct for a Fuzz Face.

The rest is down to auditioning transistors and selecting a pair that works well for you. Buying a handful of transistors of the same type should give you a wide enough range of gains to work with.

The MK1.5 is biased only slightly hotter than the Fuzz Face. Some of the "colder" MK1.5s are biased just like a "hot" Fuzz Face.

Many thanks, I'm getting the consensus is to use stock values and audition transistors, even then most should be ok as long as hfe/leakage are correct, and only tweak slightly if required.

My idea is to audition a lot of "range"  and type of transistors and see what I get out aurally that might work for me.

Hard to explain what I want in words as everyone's set ups are different re guitar, amp, room, other pedals, style etc. All I know is that I will probably know it when I hear it!

I haven't read too many times that Q1 bias is "king" though, maybe I have e overlooked that. Nearly every build I see has a trimmer on Q2.

Is there a good description/analysis that goes into that Q1 bit a little deeper?

Thanks again.

[Electric Warrior]

I don't think much is written about it, but I know it's resistor that the makers of the Fuzz Face and Tone Bender tweaked back in the 60's.

When Arbiter cloned the MK1.5 Tone Bender, they swapped the 47k resistor for a 33k, biasing the Fuzz Face a little colder. Sola Sound tweaked the same resistor in the MKII when they started using low leakage OC81Ds instead of leaky OC75s. The second stage of a MKII is essentially a MK1.5...

I think trimmers on Q2 are overrated, as they will only bias Q2. Q2's specs hardly make any difference for its bias. It all depends on Q1. If Q2's voltage is off, so will be Q1's - unless your bias problem is caused by faulty or off-spec resistors or pots.

Also, tweaking the 8k2 may cause volume issues, requiring further modifications. I don't think this is much of a problem when setting the bias on Q1.

[Gus]

Mcentee2

Do a search of this forum and the web.
Read what electric warrior posted.
Myself and others have posted about biasing FF like circuits. Almost all the resistor values matter in a FF like circuit.

[pinkjimiphoton]

everything said, plus go to geofex.com and read rg's the technology of the fuzz face.
you can voice it slightly differently a lot of ways
breadboard reccomended
500k output pot will be a bit muddier than smaller pots. i tend to like 100k or 250k.
for input cap, try the fake variable input cap trick, works pretty good and will help let the ff work with a wah in front of it. 10k-50k pot, two caps. one say, 2.2n-4.7n, and the other the stock 2.2uF... one cap to one side of the pot, one cap to the other, tie their free ends together and input to the center/wiper.. the little bit of series resistance can help mellow out high frequency noise, and ya can kinda sweep between a very bright ff and a stock one... think thin-fat pot.
you can also mess with the gain, as well as the bias, of each transistor by adding a small resistance between e and ground with each resistor if needed. i forget the exact ration, but with q's around 220 hfe or so, maybe 470r on one and 100r got me in the ballpark for a few different variants.
you'll get a tighter fuzz with the smaller caps as mentioned.
you can make the 33k resistor a mid control, check out the 69 pedal by fulltone
i applaud the breadboard approach tho. its a great way to learn the sound of the different components. try small changes in values, but don't be afraid to try unusual combinations. you can really dial in a lot of variations, its a groovy circuit.
germanium sounds better. but its a pain in the ass to work with on multiple levels.
you don't HAVE to go ge tho to get a good sounding ff tho. shoot for low gain si, or like i said, lower the gain. the e to ground connection if made directly will let the transistor reach its full gain; different from biasing from c. adding an e resistor can limit the gain of the stage and float the q so ya can get a working bias out of almost anything.
check thru this forum, you'll find THOUSANDS of good posts on the subject.

welcome to the coolest addiction ya ever got down with

[Mcentee2]

Wow! More Great advice and tips from you all, many thanks!

I have already read and digested, sometimes even understood (!), countless posts on here and other places. RG's fuzz face technology is just a good start but still leaves a lot of things to be found elsewhere re theory Vs practice.

My first set up will be a breadboard with standard values, and a range of silicon transistors to get my head in the right place for testing.

I'll move on to ge when I can successfully and accurately test for leakage/gain, so I can work out what will fit with those standard values of resistors.


Info learned so far re approach:

There is a "finite" range of the/leakage across q1 and q2 that the standard component values work for. Find transistors that work with these, and use trimmers minimally to really fine tweak if necessary for tonal quality goals (caps too).

Any far out deviation from those finite transistor  specs just leads to people using wildly increased/decreased resistors, ie they want to get *their only pair* of transistors working. I have read threads with q1 resistors up to 100k or more, and really.low or high q2 resistors too!! I want to avoid this.

Even though my goal is to have one single fuzz,  I am wise enough to known I will like lots of them😀 however I am sure I will get a range of transistor pairs I like for different reasons and then maybe build them in a modular chassis and use as I want 😀 knowing me I will just keep the breadboard on the floor permanently!

[Electric Warrior]

I'll move on to ge when I can successfully and accurately test for leakage/gain, so I can work out what will fit with those standard values of resistors.

Info learned so far re approach:

There is a "finite" range of the/leakage across q1 and q2 that the standard component values work for. Find transistors that work with these, and use trimmers minimally to really fine tweak if necessary for tonal quality goals (caps too).

Any far out deviation from those finite transistor  specs just leads to people using wildly increased/decreased resistors, ie they want to get *their only pair* of transistors working. I have read threads with q1 resistors up to 100k or more, and really.low or high q2 resistors too!! I want to avoid this.

If you're going for silicon, Q1's hfe will be the biggest variable that you can work with. Low gain silicons will give you a high voltage on Q1C and a low voltage on Q2C. Dallas Arbiter used low gainers (BC183KA) only for a very limted amount of time, but they certainly can sound good. For more "conventional" voltages with a stock setup, higher gains are the way to go. They mostly used transistors from the "C" gain group such as BC108C and BC209C.

For germaniums, measuring can be helpful and can show you what you're doing, but you will probably be fine by reading the voltages and listening.

Vintage units with germaniums will have Q1C biased anywhere between 0.3V and 0.7V. MK1.5s can measure quite a bit lower than that, easily as low as 0.15V. This results in a huge range of voltages on Q2C. It's a broad target to aim for. If you're trying several types you should be able to easily find one that biases within vintage territory. Even if not, tweaking Q1C works really well. It will still sound like a Fuzz Face even with 100k there. I've had to do it before. My transistors just weren't leaky enough to bias well with a 33k.

I've found some more info on biasing on Q1, btw. This site mentions how Q1 is used to bias Q2 instead of a base resistor: https://sites.google.com/a/davidmorrin.com/www/home/trouble/troubleeffects/fuzz/fuzz-topologies/2-transistor-english

[Mcentee2]

I'll move on to ge when I can successfully and accurately test for leakage/gain, so I can work out what will fit with those standard values of resistors.

Info learned so far re approach:

There is a "finite" range of the/leakage across q1 and q2 that the standard component values work for. Find transistors that work with these, and use trimmers minimally to really fine tweak if necessary for tonal quality goals (caps too).

Any far out deviation from those finite transistor  specs just leads to people using wildly increased/decreased resistors, ie they want to get *their only pair* of transistors working. I have read threads with q1 resistors up to 100k or more, and really.low or high q2 resistors too!! I want to avoid this.

If you're going for silicon, Q1's hfe will be the biggest variable that you can work with. Low gain silicons will give you a high voltage on Q1C and a low voltage on Q2C. Dallas Arbiter used low gainers (BC183KA) only for a very limted amount of time, but they certainly can sound good. For more "conventional" voltages with a stock setup, higher gains are the way to go. They mostly used transistors from the "C" gain group such as BC108C and BC209C.

For germaniums, measuring can be helpful and can show you what you're doing, but you will probably be fine by reading the voltages and listening.

Vintage units with germaniums will have Q1C biased anywhere between 0.3V and 0.7V. MK1.5s can measure quite a bit lower than that, easily as low as 0.15V. This results in a huge range of voltages on Q2C. It's a broad target to aim for. If you're trying several types you should be able to easily find one that biases within vintage territory. Even if not, tweaking Q1C works really well. It will still sound like a Fuzz Face even with 100k there. I've had to do it before. My transistors just weren't leaky enough to bias well with a 33k.

I've found some more info on biasing on Q1, btw. This site mentions how Q1 is used to bias Q2 instead of a base resistor: https://sites.google.com/a/davidmorrin.com/www/home/trouble/troubleeffects/fuzz/fuzz-topologies/2-transistor-english

Many thanks again, very useful.

I found the electrosmash article as well for building a fuzz face, as well as the usual well known analysis page

Now to shop for a good breadboard kit, and source some carbon resistors, trimmers, caps etc