The Anatomy of Distortion

[koula901]

When you use a pedal for either overdrive or distortion, is it to push the amp so that it would produce distortion as if you'd pushed up the amp's volume, or does the pedal itself produce those sounds. I am aware that some pedals increase the signal and push up the amp's own natural distortion, but is that also happening when reaching for high gain?

[fxdx99]

The pedal itself mostly. Yeh, can push the amp, too, but mostly the pedal effect.

 

 

Sent from a thin piece of plastic.

[mars_hall]

An amplifier as in guitar amplifier is just a series of smaller amplifier that each drive the next amplifier. Each is called a stage. The first stage is typically the one with the greater gain or multiplying factor of the input signal. The following stages have much less gain and are used to send that original amplified signal through filters that would otherwise lessen the signal. Right before the output stage, there is usually a phase inverter with no additional gain but the ability to supply as many electrons as the output tubes can use to push the speaker coils. Think of the train of stages as going from high pressure very quick movements of electrons (small pipes) towards low pressure high volume of electrons (large pipes) capable of doing the work to push the air. The number of electrons increase along the way (stages) as other electrons are sucked in along the way until you have a sizable force capable of moving the speaker coil and connected paper. You have one way valves at each stage with low pressure in one direction of flow and high pressure in the other direction. These build up.

 

Generally, the pedals these days provide the content, but that depends on the pedal. The pedals with a level control are providing a means to limit the output signal (think pressure) to what would drive the front end into saturation. Saturation is just a fancy way of saying the signal causes the the stage to use the maximum volume of electrons that can be pushed through the stage, so instead of getting large changes in direction for the majority of electrons, you start getting smaller quicker movements of fewer electrons to fill the voids at the resistive points during changes in direction. Go to the beach in Florida, look at the frequency and size of the waves. Then notice the smaller ripples in the sand at the bottom of the water. The big waves push the large objects in the water, but there is always the little harmonic currents shaping the bottom you can see in the sand. Same way with amplifiers and pedals..The energy of the wave is limited by how hard the wave can push the water up the hill. The same is analogous of the level control on a pedal. Once you start approaching that limit (edge of the water), the frequency of the ripples you see at the bottom increase but start to spread out as you get further from that limit (edge).

 

Overdrive is having the big powerboat come through temporary pushing the waves further up the shore. When the number of boats decrease, the overall smaller related ripples decrease.

 

Distortion is is putting a series of small walls at fixed distances. The overall wave gets through but the frequency of those little ripples is fixed and dependent on the distance between the barrier.

 

So distortion takes place before the wave hits the shore, overdrive carries the small harmonically related currents up the shore..

 

High gain in and of itself does not add harmonic content. If the gain of a stage wants to multiple by 100, but the source is capable of supplying a current to support a gain of 1000, no additional harmonic content is added. It is when the supply is near its limit that harmonic content is added.

 

Throw a brick in a pool and compare the upward movement of the water compared to throwing the same brick in a washtub filled to the top. Which has the greater apparent change in water movement? The volume of water and what is impeding its displacement is the limit (edges). Which has the higher frequency of waves?

[koula901]

Soooo, the pedal is pushing the amp, through gain stages to produce a sound that the amp is already capable of making? It's not the pedal actually making the distorted sound. If that is true, each pedal would sound differently through different amps, because it's actually the characteristics of the amp that is making the sound, as instigated by the pedal. Maybe I'm stating the obvious? Am I in the ballpark?

[JeffB]

Here is a demo of distortion that is created at the pedal. The amp itself could not produce this level of distortion.

The pedal generates the distortion and the amplifier amplifies it. This sound and level of gain is not in the amp.

This is not how I normally try to play. I cant do metal. This is me guessing at how some kind of metal (sludge blues rock in this case) might be played.

https://www.youtube.com/watch?v=cP68Yn5REfQ

[mars_hall]

Soooo, the pedal is pushing the amp, through gain stages to produce a sound that the amp is already capable of making? It's not the pedal actually making the distorted sound. If that is true, each pedal would sound differently through different amps, because it's actually the characteristics of the amp that is making the sound, as instigated by the pedal. Maybe I'm stating the obvious? Am I in the ballpark?

The pedal is an amplifier also and most of the coloration occurs there. If the pedal pushes the front stage hard enough, it can force the remaining stages in the path to also add. The closer they are pushed towards their limits, the more they will saturate and add the individual characteristics for that stage.

 

An important characteristic of tube amplifiers is called sag. It is a temporary lag in the ability of the power supply to deliver the needed electrons in the stages. This often occurs with tube rectifiers as opposed to quicker solid state (transistor) rectifiers. Voila, the Dual Rectifier amp with one of each which can be selected. Because of this sag, the stage reaches its limit, saturates adding the harmonics we associate with overdrive, before recovering and coming out of saturation. Some call this effect a blooming.

[AP515]

I'm still confused but that's not unusual. For me, it's about what's going through the pre-amp. Let's say you have a 2 channel tube amp. The clean channel doesn't get much gain from the pre-amp. If you put a pedal in front of the amp and stay on the clean channel you get the gain from the pedal and the power tubes create the volume. That is why the cleanest amps take pedals best.

 

When you are on the dirty channel you get the gain from the pre-amp and so you don't need a pedal to provide more (but you could used an overdrive if you just wanted crunch). Some folks don't like the gain they get from certain amps pre-amp stage and so they run a pedal in front of the clean channel.

 

Ok, how badly did I mess it up?

[212Mavguy]

Another way to get an amp to produce a distorted sound is via clean boost. That happens when you take an eq type stomp box pedal and turn the output way up. In this case there is a clean signal with more current than the first preamp stage can handle. The distortion happens in the first gain stage and is carried on through the rest of the amp. I have had fun with some old non-master volume equipped amps by hitting the front end with a strong clean boost and then using the volume knob as sort of a quasi-master volume. My Frank-en-Champ loves to be treated this way, sings for days…and the tones are great sounding, lots of harmonics created in the tube, and those harmonics are of different frequencies than solid state distortion products, the tubes' harmonics are mathematically related to the original signal because of the way that tubes work versus solid state, which don't subdivide the notes' frequencies the same way, they impose their own harmonic structures. The artful SS pedal designer can tweak that distortion type to imitate the sounds of a tube distorting, but they aren't the same. I like the clean boost better than pedals in many cases, but YMMV of course.

[koula901]

Very interesting explanations, slowly I think I'm starting to get it!

[Gitfiddler]

Another way to get an amp to produce a distorted sound is via clean boost. That happens when you take an eq type stomp box pedal and turn the output way up. In this case there is a clean signal with more current than the first preamp stage can handle. The distortion happens in the first gain stage and is carried on through the rest of the amp. I have had fun with some old non-master volume equipped amps by hitting the front end with a strong clean boost and then using the volume knob as sort of a quasi-master volume. My Frank-en-Champ loves to be treated this way, sings for days…and the tones are great sounding, lots of harmonics created in the tube, and those harmonics are of different frequencies than solid state distortion products, the tubes' harmonics are mathematically related to the original signal because of the way that tubes work versus solid state, which don't subdivide the notes' frequencies the same way, they impose their own harmonic structures. The artful SS pedal designer can tweak that distortion type to imitate the sounds of a tube distorting, but they aren't the same. I like the clean boost better than pedals in many cases, but YMMV of course.

 

@Mav212: You and I are on the same page with our respective Champ adventures. There's nothing quite like a little amp being pushed into sweet singing overdrive.

 

@Katy: An inexpensive EQ pedal might just be the trick for taking your overdrive tone to the level you seek. As stated, all OD/Distortion pedals color the sound of your amp.

[koula901]

[samwheat]

What you do is start with a load line analysis on the tube to determine what you want it to do. Then get out the resistor and capacitor decade boxes with the proper leads and clip them in the circuit and look at it with oscilloscope and then try it by ear. Changing a few things really makes production amps come alive. What most did in their designs is take the circuits right from the RCA tube design manual.

[212Mavguy]

+1, this is how the guys at the amp garage forum go about it.

[duhvoodooman]

Besides pumping up the signal gain to achieve distortion within the amp, a majority of commercial overdrive and distortion pedals artificially add distortion by use of signal clipping diodes. The incoming signal is first boosted with some manner of gain stage (usually op amps or transistors) to get the signal ampitude up into the hundreds of millivolt or even low single digit volt range and then passed through a back-to-back array of diodes, which will "clip" off the portion of the signal that is greater than their forward voltage threshold (FVT). Diodes with a low FVT, like germanium diodes (FVT typically ~0.3V) will give a greater amount of clipping and resulting signal compression than will diodes of higher FVT values, like LED's (~2 - 3V). The diodes may be located in an op amp feedback loop (the Tube Screamer and its many brethren use this method) or dump signal directly to ground from the main signal path (like the ProCo Rat). There are also pedals that use transistors directly to generate signal distortion--the Fuzz Face and Tone Bender pedals are prime examples of this approach. This tends to give a harsher, raspier sounding distortion character.

 

Koula901, you may find this informative article by effects guru R.G. Keen to be enlightening: http://www.geofex.com/effxfaq/distn101.htm

[DetroitBlues]

Some pedals are overload a signal before going into the amp (which is why the volume doesn't jump, just the gain), like my Digitech Bad Monkey. However, if I want the amps natural distoration, I push the preamp tubes by using an Electro-Harmonix LPB-1. That distoration/overdrive is from the amp itself.

[koula901]

Besides pumping up the signal gain to achieve distortion within the amp, a majority of commercial overdrive and distortion pedals artificially add distortion by use of signal clipping diodes. The incoming signal is first boosted with some manner of gain stage (usually op amps or transistors) to get the signal ampitude up into the hundreds of millivolt or even low single digit volt range and then passed through a back-to-back array of diodes, which will "clip" off the portion of the signal that is greater than their forward voltage threshold (FVT). Diodes with a low FVT, like germanium diodes (FVT typically ~0.3V) will give a greater amount of clipping and resulting signal compression than will diodes of higher FVT values, like LED's (~2 - 3V). The diodes may be located in an op amp feedback loop (the Tube Screamer and its many brethren use this method) or dump signal directly to ground from the main signal path (like the ProCo Rat). There are also pedals that use transistors directly to generate signal distortion--the Fuzz Face and Tone Bender pedals are prime examples of this approach. This tends to give a harsher, raspier sounding distortion character.

 

Koula901, you may find this informative article by effects guru R.G. Keen to be enlightening: http://www.geofex.com/effxfaq/distn101.htm

 

Thanks duhvoodooman, I'll check out the link.

[HANGAR18]

 

[tbonesullivan]

oooh boy. Giant loaded topic. For one thing, distortion usually refers to "hard clipping" pedals, while overdrive refers to "soft-clipping" pedals. You can have all the "dirt" come from the pedal, or all from the amp, or use a combination of the two.

 

The ORIGINAL overdrive was made entirely by the amplifier, either at the power tube or preamp tube level. The only way to make it happen was to CRANK IT UP. These are the pre master volume amps, which were not originally meant to make this kind of sound. However some found that when pushing their Fender Bassman or Princeton that it made a nice brown sound when pushed hard. Other companies followed suit, making amps specifically designed to be blasted and make a wonderful sound.

 

Then came the fuzz pedals, and other attempts to get that kind of sound without levelling a small city block. A lot of the first pedals were really quite harsh sounding by todays standards, as they hadn't really gotten the hang of getting a sound that resembled the ones that amplifiers made. This was resolved relatively quickly though, and by the time the Ibanez TubeScreamers and Boss OD-1 and DS-1 came out, there were also now tube amplifiers starting to use diodes to get more clipping.

 

Now, the important part to remember with pedals is that the pedal design dictates what it sounds like. Part of this is the type of device used to produce the clipping. Some use ICs (like the tube screamer) some use diodes, etc. The MXR Distortion + uses Germanium Diodes, others use LEDs, Zener Diodes, Silicon Diodes, etc. Nowadays you even see pedals being marketted by what is under the hood.

 

Now, as to the WHY this is important has to do with sound. Hard clipping sounds harsher, while soft clipping sounds more smooth. When you get into it further though, you find that a lot of the sound also has to do with the harmonics generated during the clipping.

 

Tube overdrive/distortion from the power stage tends to generate even order harmonics, which sound good. Elsewhere, you get odd order harmonics, which sound more dischordant. I'm not sure what type of clipping preamp tubes produce, but in general a LOT of filtering is needed on preamp distortion to make it sound good.

 

I've also heard that a lot of the "overdrive" in even the classic amps is actualy generated more at the phase inverter level than at the power tube level. No idea if that is true.

[koula901]

oooh boy. Giant loaded topic. For one thing, distortion usually refers to "hard clipping" pedals, while overdrive refers to "soft-clipping" pedals. You can have all the "dirt" come from the pedal, or all from the amp, or use a combination of the two.

 

The ORIGINAL overdrive was made entirely by the amplifier, either at the power tube or preamp tube level. The only way to make it happen was to CRANK IT UP. These are the pre master volume amps, which were not originally meant to make this kind of sound. However some found that when pushing their Fender Bassman or Princeton that it made a nice brown sound when pushed hard. Other companies followed suit, making amps specifically designed to be blasted and make a wonderful sound.

 

Then came the fuzz pedals, and other attempts to get that kind of sound without levelling a small city block. A lot of the first pedals were really quite harsh sounding by todays standards, as they hadn't really gotten the hang of getting a sound that resembled the ones that amplifiers made. This was resolved relatively quickly though, and by the time the Ibanez TubeScreamers and Boss OD-1 and DS-1 came out, there were also now tube amplifiers starting to use diodes to get more clipping.

 

Now, the important part to remember with pedals is that the pedal design dictates what it sounds like. Part of this is the type of device used to produce the clipping. Some use ICs (like the tube screamer) some use diodes, etc. The MXR Distortion + uses Germanium Diodes, others use LEDs, Zener Diodes, Silicon Diodes, etc. Nowadays you even see pedals being marketted by what is under the hood.

 

Now, as to the WHY this is important has to do with sound. Hard clipping sounds harsher, while soft clipping sounds more smooth. When you get into it further though, you find that a lot of the sound also has to do with the harmonics generated during the clipping.

 

Tube overdrive/distortion from the power stage tends to generate even order harmonics, which sound good. Elsewhere, you get odd order harmonics, which sound more dischordant. I'm not sure what type of clipping preamp tubes produce, but in general a LOT of filtering is needed on preamp distortion to make it sound good.

 

I've also heard that a lot of the "overdrive" in even the classic amps is actualy generated more at the phase inverter level than at the power tube level. No idea if that is true.

 

Tbone, thanks for that nice clear, easy to understand info. I've always wondered what the difference as between hard clipping and soft clipping meant. So does that mean that with a hard clipping pedal, you get more of a grinding sound? Is that what the RAT does? I also have an OCD and a TIM for overdrives. I've heard that the TIM was a more transparent pedal - does that mean it lets more of your own guitar tone shine through -or the amps, and it doesn't color the sound? I've also read that the OCD has more hard clipping. Thoughts?

[duhvoodooman]

 

Tbone, thanks for that nice clear, easy to understand info. I've always wondered what the difference as between hard clipping and soft clipping meant. So does that mean that with a hard clipping pedal, you get more of a grinding sound? Is that what the RAT does? I also have an OCD and a TIM for overdrives. I've heard that the TIM was a more transparent pedal - does that mean it lets more of your own guitar tone shine through -or the amps, and it doesn't color the sound? I've also read that the OCD has more hard clipping. Thoughts?

 

That Geofex article I linked above has a good description of how signal clipping works and how the character of the sound is changed by the degree of clipping, and the shape of the resulting waveform. In general, hard clipping tends to give waveforms with flat tops and sharp corners, which tends to emphasize higher order harmonics and give a harsher, buzzier sound. Soft clipping gives a more rounded shape and a smoother, more musical sound. Here is another very good article on the same subject, with examples of how some "famous" overdrive and distortion effects work: http://www.gmarts.org/?go=217

 

Re: your Tim and OCD pedals:

 

The Tim pedal is basically a souped up Tube Screamer with expanded flexibility and tonal control, plus an on-board boost stage. It doesn't have a ton of gain, and its reputation for transparency comes from how the EQ response of the circuit is set up. It doesn't have the very noticeable "mids hump" that the Tube Screamer and many of its brethren do, which is largely responsible for its reputation for "coloring" the output sound. There are many players who want that boost of the mids, to stand out in the mix of a band. Others value transparency. There's no "right" answer--it all depends upon what you're going for. The Tim would definitley be considered a "soft" clipping pedal.

 

The OCD kind of falls in the middle ground between overdrives and distortion pedals. It has quite a bit of gain, and the clipping is of a harder character. Still, its a smoother sound than a Rat or many of the popular fuzz pedals. While it clips signal directly to ground, typical of "hard" clipping devices, it uses a pair of MOSFETs in the clipping stage, which give a softer character, and also uses a small bypass capacitor there to reduce some of the treble harshness.

[koula901]

 

That Geofex article I linked above has a good description of how signal clipping works and how the character of the sound is changed by the degree of clipping, and the shape of the resulting waveform. In general, hard clipping tends to give waveforms with flat tops and sharp corners, which tends to emphasize higher order harmonics and give a harsher, buzzier sound. Soft clipping gives a more rounded shape and a smoother, more musical sound. Here is another very good article on the same subject, with examples of how some "famous" overdrive and distortion effects work: http://www.gmarts.org/?go=217

 

Re: your Tim and OCD pedals:

 

The Tim pedal is basically a souped up Tube Screamer with expanded flexibility and tonal control, plus an on-board boost stage. It doesn't have a ton of gain, and its reputation for transparency comes from how the EQ response of the circuit is set up. It doesn't have the very noticeable "mids hump" that the Tube Screamer and many of its brethren do, which is largely responsible for its reputation for "coloring" the output sound. There are many players who want that boost of the mids, to stand out in the mix of a band. Others value transparency. There's no "right" answer--it all depends upon what you're going for. The Tim would definitley be considered a "soft" clipping pedal.

 

The OCD kind of falls in the middle ground between overdrives and distortion pedals. It has quite a bit of gain, and the clipping is of a harder character. Still, its a smoother sound than a Rat or many of the popular fuzz pedals. While it clips signal directly to ground, typical of "hard" clipping devices, it uses a pair of MOSFETs in the clipping stage, which give a softer character, and also uses a small bypass capacitor there to reduce some of the treble harshness.

 

Duhvoodooman,

 

Thanks for the explanation. Now, I, for one, want that mid-hump boost that the green pedal (Ibenez TS9 Turbo) provides, but it seems that I can't set that up to be spanky clean. Ideally, I'd like to set that up to have it on all the time for that mid hump (maybe I should use an equalizer instead) influence, and stack it with either/or the Tim and OCD, and down the line a distortion pedal. In my set up, what I'd like to do is set up for more distortion than I really need, then clean it up by reducing my volume pot on the guitar, and when I'm ready for either a crunch sound, or more distortion, turn up my volume, or stop on a distortion pedal.

[Gitfiddler]

Koula~ From your description, it sounds like you might want one of the Hermida Zendrive pedals. I use one of the small originals and like the way it gradually goes from clean-to-mild distortion and then more distortion. Also, it doesn't seem to color the sound of your guitar or amp as much as some pedals. Players like Robin Ford have been known to just bring their Zendrive to gigs, and put it in front of a loud, clean amp (e.g. Fender Twin, etc.).

 

Check out this review:

 

http://www.premierguitar.com/articles/Hermida_Audio_Zendrive_Zendrive_2_and_Mosferatu_Review

[koula901]

Koula~ From your description, it sounds like you might want one of the Hermida Zendrive pedals. I use one of the small originals and like the way it gradually goes from clean-to-mild distortion and then more distortion. Also, it doesn't seem to color the sound of your guitar or amp as much as some pedals. Players like Robin Ford have been known to just bring their Zendrive to gigs, and put it in front of a loud, clean amp (e.g. Fender Twin, etc.).

 

Check out this review:

 

http://www.premierguitar.com/articles/Hermida_Audio_Zendrive_Zendrive_2_and_Mosferatu_Review

 

I'll check it out, thanks Tim! : )

[duhvoodooman]

 

Now, I, for one, want that mid-hump boost that the green pedal (Ibenez TS9 Turbo) provides, but it seems that I can't set that up to be spanky clean. Ideally, I'd like to set that up to have it on all the time for that mid hump (maybe I should use an equalizer instead) influence, and stack it with either/or the Tim and OCD, and down the line a distortion pedal. In my set up, what I'd like to do is set up for more distortion than I really need, then clean it up by reducing my volume pot on the guitar, and when I'm ready for either a crunch sound, or more distortion, turn up my volume, or stop on a distortion pedal.

 

The TS circuit doesn't allow for unity gain (i.e. output = input signal gain) through the gain stage of the op amp. With the Drive control all the way down, the lowest gain factor you can get is about 12. If you're at all comfortable with doing pedal mods--or have a friend who is--there's a single 51 Kohm resistor (color code = green-brown-orange-gold) on the TS9 PCB that sets the lower gain limit. You just need to solder a piece of wire across that resistor to reduce the minimum gain to 1. At that point, with the Drive all the way down, the pedal becomes essentially a clean op amp boost, but the mid hump in the frequency response will remain. That might give you what you're looking for.

[koula901]

 

The TS circuit doesn't allow for unity gain (i.e. output = input signal gain) through the gain stage of the op amp. With the Drive control all the way down, the lowest gain factor you can get is about 12. If you're at all comfortable with doing pedal mods--or have a friend who is--there's a single 51 Kohm resistor (color code = green-brown-orange-gold) on the TS9 PCB that sets the lower gain limit. You just need to solder a piece of wire across that resistor to reduce the minimum gain to 1. At that point, with the Drive all the way down, the pedal becomes essentially a clean op amp boost, but the mid hump in the frequency response will remain. That might give you what you're looking for.

 

great suggestion!