Help me understand which components do what in a fuzz circuit!

[Frizz]

I want to understand the concept behind a basic fuzz circuit. Logic tells me to start at the input and work my way to the output. Please correct my errors.

The output from a guitar pickup is AC. Fuzz circuits usually have a capacitor as the first component and a transistor as the second. I think the capacitor blocks DC and allows AC to pass. If the signal coming from your pickup is an alternating current why is this needed? Capacitors can also be used to temporarily store electricity. What effect does a capacitor have when placed between a pedal's input and the base of a transistor?

The transistor's emitter is usually connected to ground, sometimes through a resistor, sometimes not. What effect does a resistor have when placed between a transistor's emitter and ground?

A transistor can amplify the original signal. The transistor's collector is connected to the power supply through a resistor and subsequently to ground. What purpose does this resistor serve?

The transistor's collector is also connected to the output through a capacitor and subsequently to ground. What purpose does this capacitor serve?

I"m also having trouble understanding which component or combination of components set the threshold. I don't even know if that makes sense. I think the waveform from my guitar's pickup is free to be a "perfect" waveform unless affected by an outside force. I think that something in my fuzz pedal is clipping off the top and bottom of my guitar's "perfect" waveform.


Random observations I've made:

Every pin on the transistor is connected to ground. Is this a necessity?

Some resistors are variable, for example a potentiometer or a rheostat.

[bwanasonic]

I'd spend some time pondering this article. It will help with some of your questions:

http://www.geofex.com/article_folders/fuzzface/fffram.htm

A lot of basic electronics books will cover most of your other questions (whats  that resistor doing at the collector, etc). This is the one that got me started:

http://www.amazon.com/Electronics-Wiley-Self-Teaching-Guides-Kybett/dp/0471009164/ref=sr_1_3?s=books&ie=UTF8&qid=1389766582&sr=1-3

[MaxPower]

I was going to post the same link.

I would recommend the book Transistor Circuit Approximations by Malvino. Can be had quite cheaply. It covers the various transistor biasing methods. It also covers frequency response (the significance of coupling and bypass capacitors).

If you want to learn about electronics in general (about transistors, op amps, capacitors, etc.) I would recommend Electronic Principles by Malvino. You don't need the latest edition(s). Older editions can be had for $3-$10 if I remember correctly. Not as in depth on transistors, but the op amp chapters alone are worth it imo.

[dwmorrin]

Firstly, it does sound like an overall basic course in circuits is needed, but that aside...

The output from a guitar pickup is AC. Fuzz circuits usually have a capacitor as the first component and a transistor as the second. I think the capacitor blocks DC and allows AC to pass. If the signal coming from your pickup is an alternating current why is this needed? Capacitors can also be used to temporarily store electricity. What effect does a capacitor have when placed between a pedal's input and the base of a transistor?

I think the capacitor blocks DC and allows AC to pass.  You answered this yourself.  It confines the dc bias voltage at the base of the transistor to the "base-emitter" circuit.  You don't want that voltage traveling up your guitar cable into your guitar's controls, do you?
As a (broadly speaking) undesirable side-effect, it creates a "high-pass filter" effect, aka a bass cut.  The bigger the cap, the less of a bass cut.  Fuzz pedals usually take advantage of the cut effect to tame muddiness.

The transistor's emitter is usually connected to ground, sometimes through a resistor, sometimes not. What effect does a resistor have when placed between a transistor's emitter and ground?

Several things, but for basic understanding purposes, it sets the gain of the stage (smaller=more gain, larger=less gain), and input impedance (smaller=lower input impedance, larger=higher input impedance).

A transistor can amplify the original signal. The transistor's collector is connected to the power supply through a resistor and subsequently to ground. What purpose does this resistor serve?

The collector resistor allows us to create a voltage across it, and thus produce a useable "output voltage."  Without the collector resistor, there would just be an alternating current imposed over a direct current.  If our audio systems used current as a signal source, that might work, but we use voltages as signal, so we need the output to be in the form of voltage.  The resistor simply creates a wiggling voltage at the collector terminal.
I struck out that line about to ground, as I'm not sure exactly what you mean.  You mean "collector->Rc->V+->Ground?"  Then yes.  But the collector resistor itself isn't returned to ground directly if it's between V+ and collector.

The transistor's collector is also connected to the output through a capacitor and subsequently to ground. What purpose does this capacitor serve?

The capacitor you're talking about it most likely the output capacitor, and it has the same purpose as the input capacitor.  It couples the ac output to the next stage.  It blocks the dc.  For simple designs, you don't want the collector dc voltage to affect the next stage.
This output would not be directly connected to ground, but there will be a resistive path to ground, either through a fixed resistor or a volume control, usually.

I"m also having trouble understanding which component or combination of components set the threshold. I don't even know if that makes sense. I think the waveform from my guitar's pickup is free to be a "perfect" waveform unless affected by an outside force. I think that something in my fuzz pedal is clipping off the top and bottom of my guitar's "perfect" waveform.

What are we talking about?  A fuzz face?  Turn your volume down on the guitar.  Doesn't the signal stop clipping at some point?  A fuzz face style circuit is a high gain linear amplifier... it's perfectly capable of relatively clean output if your input signal is small enough.
The "trick" in a fuzz face is that the gain is so high that it quickly goes beyond what the amplifier can "cleanly" reproduce.  What are the limits?  You have a 9V power supply.  Intuitively, can you imagine the "output signal" being larger than 9V?  If the input signal is 1V, and the gain is 100, will the output signal be 100V?  Obviously not.  It will be clipped at near 9V and near 0V on the tops and bottoms.
So, the "threshold" of fuzz is set by 1) the power supply, and 2) the gain.  Note that the first commercial fuzz, the Maestro Fuzztone, used just a 3V supply, and the second version just 1.5V.

Every pin on the transistor is connected to ground. Is this a necessity?

We don't call them "circuits" for nothing.  You have to see these things as little electric loops all cleverly connected together.  Ground is also called "common" because it is shared by all the subcircuits.

Some resistors are variable, for example a potentiometer or a rheostat.

A good observation.  You've got a basic set of 3 passive components: resistors, capacitors, and inductors.  All 3 can be made variable.  All 3 have pros and cons for any given circuit.  The variable resistor is far and away the champion of the 3 when all choices are considered.  So, when you want a variable parameter (gain and volume for fuzz... treble, bass, rate, depth... etc) the go-to component is the variable resistor.

[armdnrdy]

This is good for a visual:

http://www.kitrae.net/music/big_muff_guts.html

[PRR]

Fuzzes are just audio amplifiers. You MUST understand amplifiers before you try to understand fuzzes.

> capacitor blocks DC and allows AC to pass. If the signal coming from your pickup is an alternating current why is this needed?

Because the *transistor* needs DC, un-affected by your guitar.

> What effect does a resistor have when placed between a transistor's emitter and ground? ... The transistor's collector is connected to the power supply through a resistor and subsequently to ground. What purpose does this resistor serve?

See "amplifiers".

> Every pin on the transistor is connected to ground.

Connected how? Dead-short with a wire? That won't do anything. Through a resistor low enough to BEEP a "continuity checker"? Continuity checkers are for trailer-lights, not electronics-- we need better numbers than beep/no-beep.

In general, ALL electric circuits go in LOOPs. And in most non-trivial circuits (more complicated than a flashlight) there are multiple loops. This would be overwhelming, so we combine parts of many loops on one "common" conductor. In audio we like to call it "ground", this can be misleading.

> I think that something in my fuzz pedal is clipping off the top and bottom of my guitar's "perfect" waveform.

Quite right. A "perfect" amplifier would output "any size" waveform. If the gain is 100, and the input is 1V, then it should output 100V. However we mostly use 9V batteries. So obviously anything over 9V will be clipped off. Even that is too big to go into a guitar amp, so a lot of fuzzes use other techniques to clip at 0.6V or so.

[jos.vh]

Hi.
I am also new to this forum and to building stompboxes.
My first project will be a fuzz (more precis: the Death by audio - Supersonic fuzz gun).
I have some fuzz questions in general:
Fuzz pedals come in different types, Gated, oscillating, high gain, more overdrive or distortion-like.
Which component in the schematic is responsible for the "colour" of the sound. How to make the difference between a gated fuzz or a more distortion-like pedal. Is it the hfe of the transistors or the resistors value?
Right now I do own a Devi ever Godzilla pedal, which is very gated and as a result, it is very hard to get feedback (I love feedback). Is it possible to build a fuzz pedal with relative high sustain (lots of feedback) and at the same time keep the brutal sound of the gated fuzz? Or does one exclude the other?
Anyone experience in putting 2 fuzz pedals parallel instead of in series? (one gated and one high gain to create a combination of both sounds?)

Any suggestions and/or explanations are welcome.
Thanks in advance.

Jos

[nocentelli]

The Supersonic Fuzz gun is a notoriously difficult circuit to get to work, it seems to be very picky about the transistors used. I would advise against making this your first pedal build, since failure is quite likely, which can be discouraging, although it would not be through any errors on your part. There are other designs that can provide a similar range of sounds but are less picky about parts.

Also, sustaining and gated are opposites: The reason gated fuzzes can be made to sound brutal is because you can use apply huge amounts of gain and extreme tonal shaping to the guitar signal without the guitar squealing with feedback if you stop playing for a split-second. A sustaining fuzz CAN be pretty brutal (modified Big Muff, perhaps?), but that messed-up, velcro-ripping, brutal fuzz sound tends to go hand-in-hand with "poor design" (e.g. misbiasing transistors, or using them "upside down" like the Fuzz Gun), by which I mean "against conventional norms of dirt pedal design", where smooth sustain and good response to the dynamics of your playing are the usual goals.

[Electron Tornado]

Fuzzes are just audio amplifiers. You MUST understand amplifiers before you try to understand fuzzes.

This page might help with with some of that:   http://www.beavisaudio.com/techpages/HIW/HIW.png

[jos.vh]

Thanks for the input.
I will give it a try.
A modified big muff sound nice as well.
That will probably be the next project.
I will post the results.

Jos