Question About Diode Clipping Sound

[Agung Kurniawan]

Hi guys..
Im looking for Tube-like clipping sound with some diode.
I have try some with LED, 4148 and 1n400x but still I cant get that saturating bold sound. please give me some possible diode clipper pair for me to try.

[rutabaga bob]

There are some who wire mosfets as diodes and put a germanium diode in series, one set going each way like you would normally see.

[amptramp]

This thread shows the Spark Gap, a Tube Screamer-ish variant using a pair of op amp stages with 6AL5 small signal diodes as the clippers:

http://www.diystompboxes.com/smfforum/index.php?topic=89363.0

Real tube sound from a pair of real tubes.

[ashcat_lt]

Bare tube clipping is usually pretty harsh and nasty and not really very different from diode clipping in any meaningful way.  What most people think of as "tube character" usually has more to do with other things in the circuit.  Mostly, I think, it's usually the transformers involved, but there are also things like power supply sag and just basically the tone shaping that go around the gain stages.  Then, if we're talking about tube amplifiers, the speaker cabinet itself has a lot to do with the sound you hear.

Seriously, I've tried overdriving non-transformer tube mic pres, once had one of those BlueTube pedals.  They were both really ugly and nasty and I'm pretty sure not what you actually want.

In all cases, the specifics of which frequencies are going into it, how you filter after, and exactly how hard you're hitting the "ceiling" are far more important than what exactly is causing the distortion.

[Agung Kurniawan]

is that any specific signal clipping form for tube like sound? like asymetric or maybe squarer?

[Agung Kurniawan]

the specifics of which frequencies are going into it, how you filter after, and exactly how hard you're hitting the "ceiling" are far more important than what exactly is causing the distortion.

I was build some high gain dist with Boss MT-2 tone control like and some spice at the end, well I did it simulating tube like sound from the crunch chanel of the Mesa Boogie Mark:25. its agressive, bold and also hars. but I lost a bit of clarity.
I dunno what to do but I thing I should try some diode combination.

[R.G.]

Yet another person needs to go read geofex.com.

In this case, start with Distortion 101 in the Effects FAQ.

[GibsonGM]

is that any specific signal clipping form for tube like sound? like asymetric or maybe squarer?

Also, reading about tube gain stages and how they are overdriven will help you!  http://www.valvewizard.co.uk/gainstage.html

You can make GOOD distortion with diodes and opamps, FETs, BJTs etc.  But you will not be able to make a real tube sound this way.   Tubes have properties that cause their distortion to be 'different'.   

It is a little bit involved, but maybe for now it is enough to say that tubes are more complicated than just "clippers".  Tubes are overdriven to achieve distortion, literally, and that is where "overdrive" came from.   When a signal is too large to amplify cleanly, the tube becomes very non-linear, and will hit a threshold on the positive and negative signal excursions.  These are known as grid current limiting, and cutoff.   

As a signal becomes large enough to clip, this happens gradually, not suddenly, as it does with semiconductor devices.  This creates more 2nd order harmonics, whereas diodes etc. create more odd harmonics (3rds, 5ths...).  These odd order harmonics are more harsh and fuzzy sounding, and the signal is clipped much more rapidly.   The result (usually) is that tubes seem to sound 'fatter', more compressed, less 'shrill and fuzzy'.   Between stages, tone shaping is applied, even equalization in some amps, and this is how the tone is 'finished'. 

Mesa Boogie's engineers are very talented at using these tube properties to create an awesome guitar sound   You really can't reproduce that kind of tone with just a few diodes. 

[Agung Kurniawan]

is that any specific signal clipping form for tube like sound? like asymetric or maybe squarer?

Also, reading about tube gain stages and how they are overdriven will help you!  http://www.valvewizard.co.uk/gainstage.html

You can make GOOD distortion with diodes and opamps, FETs, BJTs etc.  But you will not be able to make a real tube sound this way.   Tubes have properties that cause their distortion to be 'different'.   

It is a little bit involved, but maybe for now it is enough to say that tubes are more complicated than just "clippers".  Tubes are overdriven to achieve distortion, literally, and that is where "overdrive" came from.   When a signal is too large to amplify cleanly, the tube becomes very non-linear, and will hit a threshold on the positive and negative signal excursions.  These are known as grid current limiting, and cutoff.   

As a signal becomes large enough to clip, this happens gradually, not suddenly, as it does with semiconductor devices.  This creates more 2nd order harmonics, whereas diodes etc. create more odd harmonics (3rds, 5ths...).  These odd order harmonics are more harsh and fuzzy sounding, and the signal is clipped much more rapidly.   The result (usually) is that tubes seem to sound 'fatter', more compressed, less 'shrill and fuzzy'.   Between stages, tone shaping is applied, even equalization in some amps, and this is how the tone is 'finished'. 

Mesa Boogie's engineers are very talented at using these tube properties to create an awesome guitar sound   You really can't reproduce that kind of tone with just a few diodes.

Thank you sir, that's helping

[FiveseveN]

This creates more 2nd order harmonics, whereas diodes etc. create more odd harmonics (3rds, 5ths...).

I wonder how many more decades will this myth linger on for. Do people even remember where it started or has it become don't-wake-a-sleepwalker levels of "conventional wisdom"?

[teemuk]

There's more involved in generating "tone" of clipping than knee characteristics of the diode clipping arrangement, "cell". That's probably the least of concerns.

So, let's give a basic introductory of clipping cell's function:
Asymemmetric clipping generates -both- even and odd order harmonic distortion. The more asymmetric the clipping is the higher the amplitude of even order harmonic distortion is as well.
Symmetric clipping therefore naturally produces only odd order harmonic distortion.
In general, amplitude of distortion's harmonics increases along with magnitude of overdrive, naturally. The "harder" the clipping is the more abrupt to onset of "brickwall" clipping is as well and the higher the amplitude of higher order harmonics it introduces. With "soft clipping" one gains gradual onset to brickwall -type clipping but headroom is sacrificed to generate softer knee characteristics where, nevertheless, -some- distortion of the signal takes place anyway. It is often discernibly audible too.

Asymmetric characteristics of the "clipping cell" can be enhanced by utilising asymmetrical clipping diode arrangement (e.g. 2x+1x diode pairs), which basically just emulates asymmetry of single-ended discrete gain stages (e.g. common cathode amp) and isn't an instantenius method to achieve tone and dynamics of a genuine tube amp. Understandably. Asymmetric clipping is used creatively in well-designed "high-gain channels" or outboard effects of that nature. Sometimes symmetric characteristics are beneficial (e.g. majority of push-pull tube power amps introduce symmetric clipping distortion). Softer knee characteristics can be enhanced by using diodes that have distinctively "soft knees" in their their characteristic curves. These would be some specific germanium diodes (many of them do not have any softer knees than generic silicon diodes, only lower forward voltage) and perhaps certain types of LED's (again these often only have higher forward voltage and generic "hard" knee characteristics). FET, MOSFET or (specific) germanium BJT junctions, even tubes, can be exploited for "diode" function and these tend to have softer knee characteristics. Personally, I feel it's a ton easier to play with "input" resistor value and add some series resistance to the diodes. "Cascade" could be employed to shape knee characteristics beyond the inherent logarithmic function of diodes. So it's all trivial in the end.

But harmonic distortion is least of our worries. Whenever we have harmonic distortion applied to "complex waves" (these are all other waveforms that aren't 100% sinusoidal) the result is intermodulation distortion, which is increase of amplitude of harmonic frequencies that are no longer integers of frequencies the input waveform consists of. Guitar has distinct "timbre", which means it is an excellent example of a complex waveform. So throw concepts of "musical" even order distortion away because intermodulation distortion is bound to introduce harmonic distortion, which is discordant with frequencies that the input waveform consists of. So, in principal, whenever you introduce any harmonic distortion to the signal the intermodulation distortion will introduce an abudance of harmonic distortion, which is discordant and overall degrades "note separation". The only way to reduce IMD is by reducing the magnitude of harmonic distortion in the first place. Now, you did recall that asymmetric clipping creates -both- even and odd order harmonic distortion while symmetric clipping creates only odd order? Yes, IMD appears in lesser degree with symmetric clipping arrangements. That's often beneficial when "high-gain" tones are created because at least some note separation is still retained while chording. Did you also recall that "hard" clipping arrangements produce almost no harmonic distortion at all below clipping onset while "soft" clipping arrangements produce significant amounts of harmonic distortion whenever they are overdriven, and they just get worse the more they get overdrive. Yes: Used over-excessively that soft clipping distortion degrades note separation much more than straight hard clipping does. The mellower and subtler distortion tones are often used in context where overdrive is likewise subtler. With lesser degree of overdrive and harmonic distortion applied even asymmetric clipping will keep magnitude of IMD in moderate leash. Context is everything.

Tube amp preamps, and many more thoroughly designed solid-state overdrive circuits, are actually more dynamic. They creatively "cascade" two or several asymmetric clipping "cells" (the cell could be an entire discrete gain stage but end result is what matters) with each other. Or use various combinations of asymmetric and symmetric cells in any artistically imaginable fashion. Sometimes they adopt the fashion from a thing like an entire tube amp circuit. Anyway, this linking will dynamically alter harmonic characteristics of the overdrive because any signal asymmetry "pivots" DC offset balance between the linked cells and therefore dynamically alters the cell's inherent symmetry, or asymmetry to clip. High-gain channel may progress from producing largely asymmetric clipping to producing largely symmetric clipping when magnitude of overdrive is increased. Which is nice. So with well-thought design one can even achieve distortion with tone that changes its timbre in some preferable relation to one's picking dynamics. Nice indeed. Again not too trivial but preferences likely vary and differ just as much as people do in general.

All this IMD stuff on the other hand brings us to the context of pre and post distortion signal enhancement with filters. Imagine two conceptual circuits, A and B. Circuit A has clipping cell followed by x order high-pass filter tuned to frequency f. Circuit B has the aformentioned filter followed by the clipping cell- Their oder is just reversed, as simple as that. Both these circuits generate exactly the same pattern of harmonic distortion (at equal magnitude of overdrive) and share identical frequency response. Overdrive them and they sound completely different. Why? Because IMD.

In circuit A harmonic distortion is introduced at full bandwidth, so effectively we have the full bandwidth of frequencies to modulate together and their net effect to IMD. The post clipping cell high-pass filter will only decrease amplitude of frequencies below f, maybe the most offending "farting", but the IMD has already freaked its havoc and the signal contains harmonic distortion at abundance of frequencies. Intelligibility is probably degraded to great degree.
In circuit B, due to filter preceding the clipping cell in order, harmonic distortion is introduced in lesser degree to frequencies below f, and IMD is likewise reduced substantially because bandwidth to "fully effective" intermodulation has been reduced. The ovedriven signal is more intelligible but perhaps sounds less "thicker" than that of circuit A.
That was just an example with hi-pass filter but the concepts works the same. The filter could as well be low-pass, band-pass, band-reject, etc. The important is what the filter does in terms of overall IMD. If you study circuits with this respect you start to distinct some common themes.
Post distortion filtering can enhance the signal without IMD no longer being introduced/reduced at frequencies of question so it's effective for, say, boosting back low frequencies attenuated before the clipping cell or... Well, anyway its a powerful too for several enhancement effects and will affect timbre as much as the pre-clipping EQ, but a bit differently.

So basically, that pre and post enhancement is where you really define how clipping sounds because it is the most effective tool to alter IMD characteristics and therefore the entire timbre of the overdrive. Timbre is result of harmonics and IMD introduces a lion's share of all harmonics within distortion so need I say more...? Yes.
Those filters are often also key parts in interstage coupling between "clipping cells" so their RC time constants will have direct effect to overall "dynamics" of cascaded clipping cell arrangements.

The "softness/hardness", "symmetry/asymmetry", "dynamics", etc. these are just a tiny icing on the cake. They do introduce subtle nuances, and perhaps more importantly more "livelyness" and that "feel" where the overdrive tone interacts with how you pick those strings "just like in a good tube amp" but overall their effect to change how that distortion really sounds like is very minimal.

[midwayfair]

This creates more 2nd order harmonics, whereas diodes etc. create more odd harmonics (3rds, 5ths...).

I wonder how many more decades will this myth linger on for. Do people even remember where it started or has it become don't-wake-a-sleepwalker levels of "conventional wisdom"?

Specifically, a push-pull output stage, which is what most people claim to "want" when they talk about tube overdrive, will SUPPRESS the even order harmonics. Literally the opposite of "more even order harmonics." It's not even obscure knowledge. It's mentioned in the Wikipedia article on push-pull stages:

https://en.wikipedia.org/wiki/Push%E2%80%93pull_output

Preamp tubes aren't exactly brimming with second order harmonics.

The revised FETzer valve article on Runoff Groove talks about it as well.

Asymmetrical diodes probably just sounds more like a clipped triode (incl. transistor), assuming you can even hear the wave's symmetry and not just the Fv change.

There is still something different about how a tube clips (and especially the amp as a whole) that is extremely difficult to mimic, and almost impossibly with something as simple as a couple diodes, but second order harmonics it ain't.

[R.G.]

I wonder how many more decades will this myth linger on for. Do people even remember where it started or has it become don't-wake-a-sleepwalker levels of "conventional wisdom"?

Hmmm. Myth...

Give a read to Russell Hamm's article here: http://www.guitars-of-love.com/pdfs/TbsVsTrans.pdf. This indicates some level of reality in the thought. Just because something has been said a lot doesn't automatically mean it has no factual basis at all. The devil is always in the details.

'Course, if there is counter-information, that would be good to see too. Show us.

[FiveseveN]

Give a read to Russell Hamm's article

Yes, that's what I was hinting at with "where it started".
It compares microphone preamps at 3% THD, with zero information about their topology. A comparison of three mysterious devices is not sufficient grounds for such a hasty generalization.
Try this thought experiment: can you imagine a circuit that exclusively uses transistors and only produces even harmonics? How about a tube-based one with only odd harmonics? Did it take you more than a minute?

[thermionix]

Mesa Boogie's engineers are very talented at using these tube properties to create an awesome guitar sound

They should put that in a product and sell it.

[Mark Hammer]

Focussing on diodes, or transistors vs tubes, for the resulting tone is a bit like attributing everything about a movie to a single actor in it.  You may remember the actor and some of their lines, but somebody wrote those lines, somebody lit the scene, somebody photographed the scene, somebody gave direction, somebody selected takes and editted it, and somebody arranged for all of the technical facilities and financial backing to permit the film to have the production quality it did.  The actor did not produce the final result.

There ARE no guitar amplifiers or guitar pedals that operate on the basis of flat frequency response from 20hz-20khz.  Every single one of them has frequency shaping of some kind.  Diode clipping, and indeed ANY clipping adds harmonic content...but harmonics of what?  The relative contribution of various harmonics to the final tone is not only a function of how different devices clip; it is a function of what exactly they are clipping.  And that brings into consideration not only the guitar signal itself, but the manner in which tone is shaped through the entire signal chain and within whatever device is asked to deliberately provide clipping.

If you search through past threads here, you will find reports from people who built themselves a clone of an MXR Distortion+ and were mystified as to why they could remove the diodes completely, and still not get a clean undistorted sound.  That simple design, by virtue of some of the other things it does, and the component choices, does what it does by clipping an already clipped signal.  Few people will purposely turn their pedal output down to feed to an amp set for low gain.  They will nearly always cascade the gain of the pedal and amplifier, not to mention listen to the result through speakers that impart their own distortion.

I don't say any of those to scold anybody.  Rather, they need to always remember that what they seek is the outcome of much much more than a single component.  Brilliant movies get made with "unknowns" and marquee actors and directors make movies rejected by critics and audiences alike.  Diode choices can make a difference, the way that one can come to recognize the work of a particular cinematographer or special effects person (e.g., Ray Harryhausen movies).  But they aren't the "effect" any more than individual contributors are "the movie".  Getting the outcome you want involves thinking about all the parts, and the manner in which tone is shaped and created, throughout the circuit, and bringing everything you need together.

[GibsonGM]

This creates more 2nd order harmonics, whereas diodes etc. create more odd harmonics (3rds, 5ths...).

I wonder how many more decades will this myth linger on for. Do people even remember where it started or has it become don't-wake-a-sleepwalker levels of "conventional wisdom"?

Wow, sorry.   I didn't think it appropriate to write a novel about clipping in order to answer a beginner.  Throw some asymmetrical clipping in a tube screamer, all is well, I guess.  (?)

I didn't say "ONLY" 2nd order harmonics, and I would suggest someone who wanted to get tube-sounding distortion...read about ACTUAL tubes, perhaps Merlin's introductory book on preamps that I linked to.  And I also didn't think it would be very productive to discuss load lines, symmetric vs. asymmetric clipping without knowing if he was familiar with what they are.   

I'm more in the camp that Mark Hammer just talked about above, that ALL circuit elements affect our outcome. But the question was about diodes, and wanting tube sound.   I'll remain convinced that using grid current limiting and cutoff are what gives you 'that tube sound' and that semiconductors don't exhibit these properties, so I guess I'm a sleep walker.   It's not the whole story, no way, but it's the heart of it. 

Edit: Someone should start a thread dealing specifically with tube vs. solid state WRT clipping characteristics. 
Device parameters that affect HOW tubes enter/exit clipping compared to transistors etc. are probably the largest differences; I should have stuck more on that than even vs. odd harmonics.
http://www.theaudioarchive.com/TAA_Resources_Tubes_versus_Solid_State.htm

[R.G.]

Give a read to Russell Hamm's article

Yes, that's what I was hinting at with "where it started".
It compares microphone preamps at 3% THD, with zero information about their topology. A comparison of three mysterious devices is not sufficient grounds for such a hasty generalization.

Sorry, from the way your comment was phrased, I -didn't- think you were aware of Hamm. Hamm's paper is the earliest attempt I've found to relate the whole mess of circuit elements and practice to subjectivity by some technical approach. And there are many criticisms of Hamm's paper, both valid and invalid.

His point was to relate harmonic and IM distortion to psychoacoustics. When you say "psychoacoustics" you start walking on very soft ground indeed - especially where listening to music is concerned; the armed camps are well entrenched to protect whatever position they've staked out.

Try this thought experiment: can you imagine a circuit that exclusively uses transistors and only produces even harmonics? How about a tube-based one with only odd harmonics? Did it take you more than a minute?

]
No - but the imperfect ones took well less than a second. It's excruciatingly difficult to produce a circuit that produces only even, only odd or only anything.

And that's a good posthumous  lead in for Mark's comments. No circuit element is the be-all of anything. And the tubes-are-all camp had its origins in that it seems that simple triode circuits have something that pleases the ear, at least as practiced in simple guitar and hifi gear in the 50s and 60s, and as compared to the early transistor designs.

It's probably not a good idea to resurrect the tubes-vs-transistor wars any more here - it confuses the current crop of beginners at a minimum.

[Agung Kurniawan]

Can anyone here please explain to me what does 2nd or odd harmonics mean in simplest way?

[Tham]

There was a Youtube video of this guy trying out the many
different types of clipping.

To me, the one which sounded most natural was with NO DIODES,
i.e. which I think was just using a high value variable resistor to get
a very high gain.

The second best was using LEDs.


This guitarist in the pub below my office using the Boss GT-6, told
me he doesn't use any of the distortion effects in it, but merely overdrives
the preamp when he solos.

Of all the guitarists who plays there, I think he has the fattest and most
natural overdriven sound, with good harmonics too.