Explain to me on a 6th grade level how a tubescreamer works

[saultime]

...I just finished building my first tubescreamer clone (buildyourownclone.com), it sounds frickin' great, and I had no problems at all. But all that proves is that I know how to read instructions well

...So I read the "tubescreamer tech" thing at geofx...and a lot of it was over my head. But I still have only a very basic level of understanding, and it kills me.

So could some one explain to me, on a very very basic, 6th grade level how a tubescreamer works?

I understand that there's an op amp, but I'm not really sure what it does.  I know that there are two diodes in different directions, and they somehow clip the signal, and that's a big part of the sound...or something like that. Different parts of the frequency go to ground, some are clipped...I feel like I'm making it up now.

But on the most general level, how does running my guitar signal through all of those resistors, capacitors, ect. change the sound?

I'm sorry if this is too much of an uber noob question, but  I can't stand not understanding how this thing works.

[niftydog]

I would say that you already have a basic understanding of how it works, you're just struggling to believe in that which is intangible. (ie; that mysterious "electricity" thing.)

Well done on your first project. Your success should continue in life generally if you know how to follow instructions!

I understand that there's an op amp, but I'm not really sure what it does.

op amp stands for operational amplifier. Ignore the op bit for now, it's irrelevant. So, it's an amplifier. Do you know what an amplifier does? It reproduces the input signal at it's output, but at a higher amplitude (volume).

I know that there are two diodes in different directions, and they somehow clip the signal

You have said "clip" but do you know what that actually means? In case you don't; Picture a nice clean audio tone... a sine wave. Looks like mountains and valleys right? Now, take your imaginary scissors and chop off the tops of all the mountains and the bottoms of all the valleys. Now what do you have? You have an odd looking, squared off wavey line - that is a clipped sine wave.

This clipping is what causes the distortion that you hear.

Various degrees of clipping (soft and hard) and frequency filtering allows us to tailor the clipping to a particular portion of the frequency spectrum. That is to say that you can distort the midrange more than the high end or vice versa etc etc etc.

Diodes are used (in some cases) to perform this clipping. A diode is a very simple type of semiconductor and it's operational theory is often one of the first lessons in electronics courses. I won't go into to detail here, suffice to say that the diode does the clipping, more info can be found by following the links below.

Often you will find that a circuit looks complex when it is infact quite simple. Not all the resistors, caps and diodes have a role to play in affecting the signal - some are just necessary to allow the circuit to function properly or to give some kind of compensation or protection.

Hope that gives you a nudge in the right direction. My advice to you is to do the hard yards and read up on some basic electronics theory. A few good places to start are here and here.

[Hal]

you need to go back to the basics. Work your way up, rather than down.  Learn about DC circuits, SLOWLY test the waters of AC and frequency, then learn about semis and all that fun stuff.  

check out the Lessons in Electric Circuits free e-books.

[Peter Snowberg]

I tend to jump in head first too.

There are two (basic)  types of diode clipper arrangements.

The first type is what you find in the Rat and the distortion plus. In these pedals the diodes are connected between the opamp output and ground. Any time the opamp tries to put out more than the diode's forward voltage (about .6 for silicon or .3 for germanium), the diode will bleed off any voltage above that to ground. That chops the tops and bottoms off. One diode is used for the mountains and one for the valleys.

The second type is called a "feedback clipper" because it uses diodes in the feedback loop of the opamp. In that configuration, the opamp works as an amplifier with a high gain so long as there isn't more than .6 volts on the diodes. As soon as there is more than .6 volts in the feedback loop, the gain of the amplifier switches from a high value (as set by the drive pot) to a very low value, but it only does that switching when the tops and bottoms of the signal pass by. That super rapid adjustment of gain results in a different sound of distortion which has more even-order harmonics than the diode-to-ground style clipper from the distortion+.

The second style of clipper circuit usually has a second source of distortion too. The gain of the opamp asks the chip for more output voltage swing than it is able to provide so you have that distortion from running out of headroom in addition to the diodes. Try lifting one side of the pair of diodes to hear the opamp distortion only.

It may seem a little like magic at first, but it will all sink in. Try to take any circuit apart into the most basic chunks you can. In the end it's all resistors, capacitors, and transistors. The magic is all in the connections between them and the component values.

[Mike Burgundy]

Basics are really the way to go. A lot of those resistors and capacitors are in there just to get the amplifier bits to work properly. Some actually do something to your sound.
See if you can get some reading under your belt. Basic capacitor and resistor stuff, and such. We're here to help if anything is still confusing.

That said - I don't even know the finer points of DC operation...I try to avoid calculating, and if I have to, I only know where to find the how-to, not the formulas by heart.  Having *all* the theory down isn't a must to have a feel for and understanding of what's going on. The basics, however, are essential.
I wish my first project - when I didn't have a clue - had worked like yours did!

[MartyB]

That just might be the coolest/most informative question, and response posts I've seen on opamp and diode function.  At least for my level of understanding! Thanks!
MartyB

[saultime]

Thanks guys--this is EXACTLY what I wanted. If anyone else knows of more websites with good basics they can point me to, that would of course rock. Or books even. Here's a picture of my screamer:



I replaced the red LED from the kit with a blue one for mojo factor. It's so damn bright though, I hope it's not a problem...

[ninoman123]

Woah. looks better than my screamer, nice paint job man

[bwanasonic]

Where's that durn cook your own distortion article... Ah, here it is:

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


This is a good reference if you haven't seen it (and an even better one if you have :wink: ) .

Kerry M

[Connoisseur of Distortion]

your first build is a tubescreamer, you have an incredible paint job, and it works first try.

my first build was an electra in a black ABS box, and shorted out once i placed it in. after, of course, a good 2 days of debugging.

beautiful first project!

[saultime]

In the intrest of full disclosure, I have a couple other nerdy hobbies that make is so i've had experience painting things.

I'm always sort of shocked by how easy it is to mess things up with a spray can. I'm amazed anyone can do it right, let alone me. Practice helps.

[Alpha579]

wow, really nice job with the 'screamer! great paint work!

[Satch12879]

You might want to invest in one of those spray paint can handles, which is kinda like a trigger you attach to the top.  Almost makes it look like you're working a air gun.

[nelson]

WOW, buildyourownclone.com is expensive. 75 bucks for a tubescreamer clone. Great for beginners though.

[GreenEye]

Nice first build.  Sorry, I can't help with the understanding part.  I treat this like guitar - if I do it long enough, it'll somehow sink in.

[mrsage]

WOW, buildyourownclone.com is expensive. 75 bucks for a tubescreamer clone. Great for beginners though.

Yeah, they're great for beginners, but probably a bit expensive for more experienced folks.

He sells super high-quality boards for very reasonable prices, though.

[saultime]

Yeah. The board is NASA quality. And it's nice to have a pre-drilled enclosure. He also ships insanely fast. It felt good throwing a little business his way

Next time I'll just get the board, and round up the parts myself. Ross clone, here I come...

[inverseroom]

Thanks a lot, you guys.  I've been wondering how the hell a diode to ground could do jack shit to a signal--it didn't occur to me that this was how diode clipping worked.  Suddenly I understand a whole bunch of stuff better...