How do I design a circuit?

[bldyi]

Hello,

The other day I decided it would be fun to create a distortion pedal for myself.
Could someone please help direct me to a site or a book which describes or teaches guitar pedal circuit theory?
I see all the schematics but don't understand why they are laid out the way they are.
Also where can I learn which value ohms and Faradays to use in the the designs?
I really don't want to blow out my amps.

Thanks

PS. Yes I am a noob at this.

[twabelljr]

Read GEOFEX. Link top left. Tons of great information. The "Technology of the ..." articles found there explain complete circuits using the schematic. Lots of good references in the Links tab above also. DIY FAQ, GEO FAQ too. You can learn a lot from this forum alone!

[digi2t]

Electronic Projects for Musicians is very good.

First and foremost, I recommend reading Geofex " Building your own effects" page, http://www.geofex.com/effxfaq/bldfx.htm
It's a very good first step, which includes a biblography.

[defaced]

In a general sense, building your own pedal is just applying very basic circuits in somewhat unique ways.  So if you can learn the basics, you fill find your world wide open to possibilities.  In addition to the great links already provided, check out the series of threads here, this might not be exactly right, but they were started by Dano (beavis audio) and explained what each part in a circuit did.  I think they were called the "technology of ..." threads. 

[Kesh]

Following from what defaced said.

For the very simplest thing, learn how a common emitter amplifier works.

This is the basis of many pedal circuits. It's a clean voltage amplifier with one transistor and half a dozen other parts.

Then learn how to pick resistor values that will overdrive it (small amount of maths involved to work out gain), or how to put resistor/cap sections that will change the tone (some maths about frequencies), or add diode clipping feedback to it.

[alex_spaceman]

The sources mentioned above are all good and very informative. Speaking of distortion pedals, this is a pretty interesting read that will give you a couple ideas in terms of how to tweat and customize a circuit to your needs.
I wouldn't worry too much about blowing your amp up, but check your polarities when using diodes/electrolytic caps etc...!

EDIT: forgot to actually link the page I mention in the post...! Here it is: http://www.generalguitargadgets.com/richardo/distortion/index.html

[smallbearelec]

Creating something completely original is way beyond what what most DIYers (including me) can do. That takes a detailed knowledge of theory, the math that describes the operation of devices, and a very creative imagination. As others have noted, however, combining circuit "blocks" into something you like is a much more reasonable proposition. First, you learn how some of the blocks work and what they do, then maybe modify the operation of a block and try it in combination with others.

So how do you learn how the blocks work?

One way to start is with a solderless breadboard:

http://www.smallbearelec.com/servlet/Detail?no=374
http://www.smallbearelec.com/servlet/Detail?no=714

This kind of tool will let you set up a simple circuit and make it work without committing to one particular soldered build. There are numerous on-line tutorials (some at my site) that will walk you through the process, and other references that will explain what various components do. It's a long process and not easy, but very satisfying.

Happy Construction!, and stay in touch here as you learn.

SD

[bldyi]

Guys,

Thanks so much for the info.
I have taken tons of physics classes so the math and schemes are not real problems. They just never taught me practical application towards guitars.
So I'm gonna get a diy kit and go from there. I get that if you replace the types of components you get a different sound but where  can i find the output voltage magnitude of a pedal. The question i cant seem to get an answer to is what is the value of a guitar output current and then the value an amp can accept?

Thanks again

[R.G.]

With the math background, you're a good step ahead on the path.

A guitar pickup looks like a signal voltage of perhaps 100mV to 1V peak, in series with 4K to 20K of resistance and 2-4 Henries of inductance. It has enough distributed internal capacitance to cut off output signal dramatically above 4KHz to 8kHz.

You'll need to understand frequency spectra and be able to translate in your head between time domain and frequency domain on signals, at least in an intuitive if not quantitative way.

Go learn Ohm's law in all of it's applications. This will seem trivial to you at first glance, but trust me, learning to use that simple three-variable equation the right way is much like learning to play guitar - it's the easiest instrument to play poorly and one of the hardest to play well.

Learn what impedance is, and how to calculate frequency response of simple single R-C circuits in all four variations.

Learn what Thevenin and Norton equivalent circuits are and how to transform between them and to reduce schematics to their Thevenin/Norton equivalents. Ideally you should be able to do this in your head while looking at a schematic.

Read about electronics, and study circuit designs and schematics. Start now, spend from one to 10 hours a day at it until you decide you'll never design another circuit. I've been at it for over 40 years now. You'll learn something new every time you read.

[bldyi]

Thanks R.G.

I'm gonna get started right away.
Say I reduce a basic circuit such as http://www.geofex.com/Article_Folders/fuzzface/fffram.htm to its total internal resistance, capacitance etc. what would happen if i change the components and add more resistance or capacitance into it?
So for example i get a breadboard (ordering one online in a bit, kinda want the beavis board) and set up this schematic, what happens if i replace the final 500k resistor with 750K or even get rid of it?
What I really need to know is where do I draw the line before the amp is blown?

Thanks gain,

sorry for stupid questions.

[R.G.]

sorry for stupid questions.

They're not stupid questions. They're just beginner questions, which you are, and that's OK. We were all beginners at one time.

Say I reduce a basic circuit such as http://www.geofex.com/Article_Folders/fuzzface/fffram.htm to its total internal resistance, capacitance etc. what would happen if i change the components and add more resistance or capacitance into it?
So for example i get a breadboard (ordering one online in a bit, kinda want the beavis board) and set up this schematic, what happens if i replace the final 500k resistor with 750K or even get rid of it?

One problem all beginners have is that they think they need facts and details. While that is true, and there is a huge amount of facts and details that need to be learned, there is also a huge body of less-detailed, more-general knowledge that is needed too. This additional stuff goes under the general name of "experience". Experience can loosely be described as the sum of a huge number of previous events that happened to you. Experience can only be obtained by doing or seeing things yourself, not from learning equations.

This question gets several answers from my experience. One is that is it not possible to give a single answer to "what would happen if i change the components and add more resistance or capacitance into it? " without knowing exactly which resistor and/or capacitor you mean. They all do different and possibly interactive things. The easiest way to get some experience with this is to get a circuit simulator program and play with the values in the simulator. Failing that, use a breadboard. Even better is to go learn about bipolar transistors and how they operate and write the equations for what voltages and currents happen as a result of which values, then change the values to see what happens.

What I really need to know is where do I draw the line before the amp is blown?

This is another one that experience answers. If you have a generic guitar amp based on vacuum tubes and it's not already damaged in some way, then you can largely do anything you want in a pedal circuit that's powered by a 9V battery or DC supply. In general, tube guitar amps will not be damaged by anything a 9Vdc powered pedal can do to the input. Notice that this requires experience about amplifiers, not just pedals and circuits.

The reason I keep mentioning experience is that you should expect to keep running into places where you need to know more. Do not get discouraged because you make mistakes, or don't know how something works. Instead, take that as a chance to go learn how not to make mistakes the next time.

I once heard that good parents arrange things so that children can make their own mistakes and learn from them. The parents' job is to ensure that the consequences of the mistakes are non-fatal and non-damaging. You're not a child, and I'm not a parent, but in the spirit of that idea, here's one bit of advice: working with 9Vdc powered circuits is VERY different from working with AC mains power circuits. A mistake on AC mains power circuits can cause instant injury or death. Do anything you like with 9V battery powered circuits (except perhaps directly shorting the battery) and you're fairly safe. DO NOT work with AC power wiring or circuits until you have been trained and supervised in how to do it safely and already know how to do it right before you start.

[teemuk]

I would start from making a trip to local library or bookstore and getting a decent textbook about analog electronics. Not a tome in biblical proportions like "Art Of Electronics" but something that is somewhat lighter reading ...say about 200 pages.

There's a good selection of those kinds of books and about all of them guide through pretty much all the basics in overall electronics theory (ohm and current laws, basic components, etc), filters, power supplies, transistors, opamps, architectures of various gain stages, oscillators and power amplifiers, and so on. Pretty much everything else but tubes in the essential 101 format.

Try, for example, Ian Hickman's or Crecraft/Gergery's books. Something commonly used in teaching first year students on the matter.

With your skill level I'd read at least one such book before even daydreaming about designing stuff from scratch.


...oh. Persistant search will probably even find one or two of such books in ebook format. I still would rather get a real book. It's much easier to read and use as a reference.

[Kesh]

Thanks R.G.

I'm gonna get started right away.
Say I reduce a basic circuit such as http://www.geofex.com/Article_Folders/fuzzface/fffram.htm to its total internal resistance, capacitance etc. what would happen if i change the components and add more resistance or capacitance into it?
So for example i get a breadboard (ordering one online in a bit, kinda want the beavis board) and set up this schematic, what happens if i replace the final 500k resistor with 750K or even get rid of it?
What I really need to know is where do I draw the line before the amp is blown?

Thanks gain,

sorry for stupid questions.

You could go even simpler than the fuzz face and look at the electro harmonix LPB-1



see what happens to volume and distortion if you change the 360 or the 10k

and what happens to tone if the 0.15 caps are lowered.

[bldyi]

https://www.circuitlab.com/

This lets circuit simulation and its free and awesome. thanks for all the advice guys.

[bldyi]

Nope. What am I missing?
I see the values are changed but what does that do in relation to tone?

I'm off to library to find some reading stuff about this.

[Kesh]

https://www.circuitlab.com/

This lets circuit simulation and its free and awesome. thanks for all the advice guys.

If you're into simulation get hold of LTSpice.

Simulation isn't any good for telling you the tone of distortion, though it will give frequency response.

[ashcat_lt]

LTSpice actually will tell you something about the tone of distortion.  Transient analysis shows what you can expect it to do in an oscilloscope kind of way.  If that's not good enough, you can have it spit out a .wav file using either the internal sources or another .wav file as input so you can actually hear some approximation of what it will do.

[darron]

I'm on my phone and haven't read the whole thread properly, but this could help you out massively:

http://www.generalguitargadgets.com/richardo/distortion/index.html

http://www.diystompboxes.com/smfforum/index.php?topic=47235.0

[PRR]

> where do I draw the line before the amp is blown?

Rough answer: don't worry about it. Guitarists plug-in the darnest things. Amplifier makers have learned to make amp inputs VERY robust, to reduce warranty claims and bad reputation.

Within limits. A 300V supply through a 5K resistor will blow-up many things. Your amp, your heart, etc. It's hard to do such damage with 9V, especially a battery, even if shorted (it may burn your skin but not paper).

> what does that do in relation to tone?

Ah, there's the rub. Your ear is a complicated and strange device. It ignores some things and focuses on others.

Anyway, "it's all been done before". Fuzz is older than amplifiers: Elisha Gray's telephone patent is totally fuzz, and Bell's telephone would fuzz on a loud voice. That's bad for conversation, so Bell improved (by buying a different less-fuzzy microphone). All amplifiers will fuzz if you hit them harder (or feed them less). There's excellent theory how to avoid that: break the rules.

However slightly different distortions can have very different effects on the ear. And there's no concise knowledge of that.

I can design an amplifier. I can tell you how to make it fuzz. I can NOT tell you what the fuzz will sound like, musically, except in very broad terms. Especially for the large transients of plucked strings (guitars).

So plagiarize then modify. Everybody in audio does. Some things can hardly be improved. Other things have a broad range of possibilities, you may find a variation you like better. And it can be hard to predict in advance what circuits are mod-happy and what circuits come out "ugh!" for most any mod.

[bldyi]

> where do I draw the line before the amp is blown?

Rough answer: don't worry about it. Guitarists plug-in the darnest things. Amplifier makers have learned to make amp inputs VERY robust, to reduce warranty claims and bad reputation.

Within limits. A 300V supply through a 5K resistor will blow-up many things. Your amp, your heart, etc. It's hard to do such damage with 9V, especially a battery, even if shorted (it may burn your skin but not paper).

> what does that do in relation to tone?

Ah, there's the rub. Your ear is a complicated and strange device. It ignores some things and focuses on others.

Understood.
Thanks so much. Gonna built my beavis board and take it from there.
All you guys on this site are awesome. If it works ill post my stuff.

Anyway, "it's all been done before". Fuzz is older than amplifiers: Elisha Gray's telephone patent is totally fuzz, and Bell's telephone would fuzz on a loud voice. That's bad for conversation, so Bell improved (by buying a different less-fuzzy microphone). All amplifiers will fuzz if you hit them harder (or feed them less). There's excellent theory how to avoid that: break the rules.

However slightly different distortions can have very different effects on the ear. And there's no concise knowledge of that.

I can design an amplifier. I can tell you how to make it fuzz. I can NOT tell you what the fuzz will sound like, musically, except in very broad terms. Especially for the large transients of plucked strings (guitars).

So plagiarize then modify. Everybody in audio does. Some things can hardly be improved. Other things have a broad range of possibilities, you may find a variation you like better. And it can be hard to predict in advance what circuits are mod-happy and what circuits come out "ugh!" for most any mod.