Someonehelp me understand how a transistor creates distortion

[camojoe]

I have successfully built my own fuzz pedal on a breadboard, however now I want to create a simple distortion pedal. I have general knowledge of how the base of the transistor dictates how many electrons flow through the collector just like a tube would in an amp. However, the emitter of this transistor is grounded. My confusion is where does the signal go after the amplification of the transitor? My best guess is it goes out of the collector but can DC current from the battery go in at the same time an amplified AC current goes out the collector as well? I hope that makes sense, I know how the components work, I just don't where the flow of everything goes. Hope to hear back soon, thanks.

[GibsonGM]

Hi Joe,

Good question, and will take you a few more questions to understand, probably!  Back of envelope thing here:   The common emitter transistor amplifier you posted...yes, the amplified AC signal is taken from point 6, from the collector, in THIS 'topology'.   Other types of circuit design will take the signal from elsewhere, such as the emitter, but leave that for now.    In the CE amp here, the signal will be inverted 180 degrees from input; worth noting.   

You seem to know that DC is used to do this amplifying, good...a current is set up to flow from collector to emitter, and is controlled by the base.  This is a DC current.  The input capacitor (1) and output capacitor (6)  "keep" this DC level inside the transistor circuit.    The AC comes in thru (1), and is applied to the base.  This modulates the quiescent current flowing thru collector >emitter to create "a larger version of the base current".    It is now amplified.   In a properly designed amplifier of this class, both the upper and lower wave of the AC signal will be amplified....biasing makes it ride on a DC level.   When this signal is taken thru the output cap, the DC bias is blocked, so the signal you get is just a larger version of the AC you input, with no additional DC present!

"The current flowing from collector down thru the emitter to ground has been changed - controlled - by the current flowing from base to ground".

The 'superposition theory' of electricity dictates that AC and DC can exist together, so yes, 'more' DC can flow in at the same time the (inverted) AC signal that has been amplified is taken from the collector.  This IS similar, in very many ways, to how a triode amplifier works.   You can mix AC and DC, then UN-mix them again, you can bias AC to 'ride on a DC level' (we do this all the time!  Resistor "5" is doing that in your pic).   

Hope this helps some!   Welcome to the forum!   You may have more questions, and that's a good thing   There are MANY 'basic transistor amplifier' vids on UTube....

> If the amplifier is designed to give faithful, LINEAR reproduction of the AC input ("hi fi"), it has little distortion.   If you bias it to cut off part of the upper or lower part of the AC signal - like trying to shove a 12" high book on a 9" high bookshelf - then it makes distortion; you're making it amplify in a NON-LINEAR fashion (that's a 'key term').   This is only one way to do so...you can do it by how you bias the input, and also by overdriving the input with 'too high' of a signal...one stage is usually not enough to generate much distortion on its own unless grossly overdriven.

[PRR]

> can DC current from the battery go in at the same time an amplified AC current goes out the collector

That's why you "always" have a collector resistor (or substitute).

You didn't get the the question in your Subject. Distortion is usually from amplifying the signal bigger than the amplifier can deliver. Your circuit has a gain over 100. If you put in 1 Volt, it should put out 100 Volts. But it only has 9 volts to work from! So at least 91 of the expected volts won't happen.

[Rob Strand]

There's two mechanisms of distortion: Linearity and clipping.

A simple division of the two is:

Transistor, tubes, JFETs, virtually any device is non-linear.   Even the current gain of a transistor is dependent on the actual current.   The non-linearity causes distortion.    This type of distortion is what most HiFi people are interested in. 

However, pretty much all distortion pedals use clipping as the primary mechanism for creating distortion.   A transistor both amplifies a signal and has a limited power supply voltage.  When the output signal level exceeds the supply capabilities it clips.

[camojoe]

Hi Joe,

Good question, and will take you a few more questions to understand, probably!  Back of envelope thing here:   The common emitter transistor amplifier you posted...yes, the amplified AC signal is taken from point 6, from the collector, in THIS 'topology'.   Other types of circuit design will take the signal from elsewhere, such as the emitter, but leave that for now.    In the CE amp here, the signal will be inverted 180 degrees from input; worth noting.   

You seem to know that DC is used to do this amplifying, good...a current is set up to flow from collector to emitter, and is controlled by the base.  This is a DC current.  The input capacitor (1) and output capacitor (6)  "keep" this DC level inside the transistor circuit.    The AC comes in thru (1), and is applied to the base.  This modulates the quiescent current flowing thru collector >emitter to create "a larger version of the base current".    It is now amplified.   In a properly designed amplifier of this class, both the upper and lower wave of the AC signal will be amplified....biasing makes it ride on a DC level.   When this signal is taken thru the output cap, the DC bias is blocked, so the signal you get is just a larger version of the AC you input, with no additional DC present!

"The current flowing from collector down thru the emitter to ground has been changed - controlled - by the current flowing from base to ground".

The 'superposition theory' of electricity dictates that AC and DC can exist together, so yes, 'more' DC can flow in at the same time the (inverted) AC signal that has been amplified is taken from the collector.  This IS similar, in very many ways, to how a triode amplifier works.   You can mix AC and DC, then UN-mix them again, you can bias AC to 'ride on a DC level' (we do this all the time!  Resistor "5" is doing that in your pic).   

Hope this helps some!   Welcome to the forum!   You may have more questions, and that's a good thing   There are MANY 'basic transistor amplifier' vids on UTube....

> If the amplifier is designed to give faithful, LINEAR reproduction of the AC input ("hi fi"), it has little distortion.   If you bias it to cut off part of the upper or lower part of the AC signal - like trying to shove a 12" high book on a 9" high bookshelf - then it makes distortion; you're making it amplify in a NON-LINEAR fashion (that's a 'key term').   This is only one way to do so...you can do it by how you bias the input, and also by overdriving the input with 'too high' of a signal...one stage is usually not enough to generate much distortion on its own unless grossly overdriven.

Thank you very much! I admire your knowledge. Way better of an answer than I can find anywhere online XD. However like you predicted I do have a few more followup questions. You mention that the output cap(6) draws amplified ac signal riding on a dc level. Therefore the signal gets pulled out of the collector from what I understand. So if that's true you also mention a quote "The current flowing from collector down thru the emitter to ground has been changed - controlled - by the current flowing from base to ground". That makes it seem like the signal also goes to ground? Unless the signal doesn't follow the current? and this may sound dumb but does that signal go back to the 9v battery from ground? where does it go if not? Sorry for all of these questions, its just not as straightforward as a simple circuit that goes all in one direction haha.

[camojoe]

I guess to summarize my confusion is where does the amplified signal go from the transistor to eventually get to the output cap(6)

[PRR]

> where does the amplified signal go from the transistor to eventually get to the output cap(6)

Don't tunnel-vision on the transistor! A solo transistor can NOT amplify!

This type amplifier is a "fair fight" between the transistor and the collector *resistor*.

[antonis]

Maybe a "confusion" should be settled here..

Signal comes from 1, passes through 2 and 4 and ends up to Ground..
(original signal is completely lost here..!!)

Another "confusion" settlement should be:

VOLTAGE on Base controls CURRENT on Collector..
(Base current could be considered as an "annoying" imperfection rather than the real cause of transistor operation..)

[GibsonGM]

You might choose to think of - all the signal that you do not 'take from' the transistor goes back to ground.  If you're 'tapping off of it', it goes where you tell it to     To go much beyond this kind of understanding of how the transistor operates, you'd have to enter into the world of the electrical engineer, ha ha.   Maybe, as PRR is hinting at...think of this as a voltage divider!   Collector resistor, AND the transistor, working together.   The transistor changes its resistance based on the current applied ("transferred resistance"...transistor). 

There is much we can explore without having to get into physics, such as how to bias the transistor properly, how to graph its operation, different 'classes' of operation.  That's pretty much where I stay, by choice.  I haven't found any benefit in going too much further than that! 

[camojoe]

I get that the collector resistor changes based on the voltage of the ac signal from your guitar. But my confusion lies where the signal goes after it gets amplified. Antonis partly answered my question where he states "Signal comes from 1, passes through 2 and 4 and ends up to Ground..(original signal is completely lost here..!!)" If the original signal is completely lost here, I wanna know where the amplified signal goes from the transistor. I believe you might have answered that Gibson where you state

the amplified AC signal is taken from point 6, from the collector, in THIS 'topology'. 

I believe you are saying point 6 takes the AC signal from the collector, it just confused me a little cause you said the signal is taken from point 6 meaning its going from point 6 back to the collector. If what I believe you said is what you meant, then I believe that answers my question about where the signal goes from the collector. To clarify the original signal gets taken out the emitter into ground and the amplified signal goes out the collector straight to the output capacitor (6).

[antonis]

If the original signal is completely lost here, I wanna know where the amplified signal goes from the transistor.

I believe that answers my question about where the signal goes from the collector. To clarify the original signal gets taken out the emitter into ground and the amplified signal goes out the collector straight to the output capacitor (6).

Very brute approximation but very true, also..!!

P.S.
Signal is refered to instantaneous voltage difference between two distinct points so its instant amplitude value depends on the points refered to..
(on a CE amplifier, signal amplitude can be measured between Collector & Ground or Collector & Power supply - same magnitude but opposite phase..)

[camojoe]

Thank you! and because the original signal goes to ground the amplified wave form wont cross out any of the original frequencies since they aren't both being outputted?

[antonis]

As far as amplified signal is a flawless(or not)) replica of the original one, it can't be any frequency distinction..

Amplified signal is a brand new signal (from incoming source point of view) of exactly the same with the original frequency..
(in case of they were mixed, there should appear a partial(Gain dependent) cancellation of amplified waveform due to amplified signal phase reversal..)