A lot of really famous overdrive pedals double up the 1N914 diodes in the feedback loop. Gainster, Red Snapper, Timmy, Xotic BB, Wampler Ecstasy/Euphoria, Barber LTD, Barber Gain Changer, etc.
What is the reason? I understand why you'd use two diodes one on side for asymmetrical clipping. But why two on the same side?
I know it increases the clipping threshold. But once you turn up the gain, won't it sound the same (as long as you tune the feedback cap to get the same treble response)? And in that case you're boosting noise too, just to get the same amount of clipping.
Does it give better control of the gain knob for low gain? Couldn't you simply limit the max gain to get that result?
Does the "softness" of the diodes double up in some way? Extra soft clipping if you stack a pair of Mosfets?
Or is it just to keep the output volume higher, so you don’t need an output boost to compensate like you might on a Distortion+?
EDIT: for example:
(https://i.postimg.cc/rR6v103L/Screen-Shot-2023-02-11-at-6-42-27-PM.png) (https://postimg.cc/rR6v103L)
There's a few reasons:
- It sounds different.
For a non-inverting clipper the clean signal leaks through with a gain of 1.
With two diodes the clip voltage is 0.6V and is effectively blended with the clean signal.
With four diodes the clip voltage is 1.2V the distorted signal is now 2 times higher
but the clean signal is the same - so more diode sound.
- In some cases the two diodes are just use as a clipper to prevent the opamp from clipping.
That means the sound largely comes form the diodes and not the opamp.
IMHO the asymmetrical argument isn't the primary reason. The 2 + 1 diode format is more like an in between
of the two above cases. If you listen to the asymmetric case it sounds in-between the two symmetric diode
cases, it doesn't possess any magic second harmonic tone.
> But once you turn up the gain, won't it sound the same
If you have to turn it up, it must be weak. Am I right?
You NEVER want to be the "weakest" pedal in the showroom.
Quote from: Rob Strand on February 11, 2023, 07:32:18 PM
With four diodes the clip voltage is 1.2V the distorted signal is now 2 times higher
but the clean signal is the same - so more diode sound.
More _undistorted sound that is proportionately less clipped_... which is more similar to the original,so LESS diode sound, no?
QuoteMore _undistorted sound that is proportionately less clipped_... which is more similar to the original,so LESS diode sound, no?
It's a little tricky to construct an apples to apples comparison. One angle is you want to compare the clippers with same input level but also the same diode current (since the diodes are then active the same in both cases). That means the feedback resistor needs to increase by a factor of 2. Of course the output level will go up but then you can adjust the levels with an output attenuator.
If you think about comparing a 20 diode clipper to a 2 diode clipper clearly you need to make some changes to have any hope of comparing the underlying *tone* without the levels entering the equation. (Assuming the opamp won't clip, but on 9V it will :icon_mrgreen:).
For things like Timmy and the OCD the clip voltage has an impact on choosing the gain of the second stage. The second stage can clip or not clip, it's a design choice.
Quote from: PRR on February 11, 2023, 09:35:05 PM
> But once you turn up the gain, won't it sound the same
If you have to turn it up, it must be weak. Am I right?
You NEVER want to be the "weakest" pedal in the showroom.
Fair enough haha! Louder sounds better!
Quote from: Rob Strand on February 11, 2023, 07:32:18 PM
For a non-inverting clipper the clean signal leaks through with a gain of 1.
With two diodes the clip voltage is 0.6V and is effectively blended with the clean signal.
With four diodes the clip voltage is 1.2V the distorted signal is now 2 times higher
but the clean signal is the same - so more diode sound.
Hadn't thought of the ratio of the 1x clean and the clipping, interesting!
That's at least something beyond the simple "it's louder" because of the higher threshold haha!
I think I'll try some level-matched examples in spice to see if that comes through...
ok, here's the result of a test clipping a sine wave:
(https://i.postimg.cc/t1g6Cdsm/Screen-Shot-2023-02-12-at-12-57-46-AM.png) (https://postimg.cc/t1g6Cdsm)
(https://i.postimg.cc/bD7STK3K/single-vs-double-diodes-frequency-response.png) (https://postimg.cc/bD7STK3K)
in the double diode circuit, i halved the value of the feedback cap, doubled the value of the feedback resistor, and reduced the volume of the output.
i had to reduce the volume by different amounts for the frequency graph and the clipping graph.
i didn't expect it, but looks like the single diodes have a more linear knee after the clipping threshold is reached?
It can be a bit of an illusion due to adding different amounts of clean!
If you plot the voltage across the 4xdiode/2 and the voltage across the 2xdiodes you get an identical waveform meaning the diode part is doing the same thing except double the voltage.
From that we know if we double the output of the 2xdiodes, that the diode voltages must agree with the 4xdiode. The theory is the 2xdiodes case has one clean blended, and the 4xdiodes has one clean blended. If we double the 2xdiode output signal we get 2xdiode + 2xclean blended, and if we then subtract one clean we expect it should match the 4xdiode+one clean blend.
This set up shows they are in fact the same,
(https://i.postimg.cc/MnpqrMyY/Clipper-1-D-vs-2-D.png) (https://postimg.cc/MnpqrMyY)
Back in July 2022 I posted these sims showing explicitly that the non-inverting clipper is the same as a clean blend.
(differences only due to finite opamp bandwidth.)
(https://i.postimg.cc/fJK855jJ/clipper-blend-schematic.png) (https://postimg.cc/fJK855jJ)
(https://i.postimg.cc/dkrBC9VQ/clipper-blend-waveforms.png) (https://postimg.cc/dkrBC9VQ)
Rob, I understand just adding a pair of diodes (and everything else equal) to get a different sound (signal clipped at different point) was the whole point.
Unless I'm misunderstanding.
Quote from: bartimaeus on February 11, 2023, 06:36:35 PM
Or is it just to keep the output volume higher, so you don't need an output boost to compensate like you might on a Distortion+?
Mostly this, I'd say. A 0.6V signal isn't that loud. If you've got anything that does any sort of boosting ahead of the drive, the distorted signal might even finish up *quieter* than it went in, especially if it's an inverting clipper. Doubling up the diodes gives you more level to play with.
Yes, it affects the clipping level, so you need more gain to get the same amount of clipping, but that's not such a big deal as all that.
Quote from: marcelomd on February 12, 2023, 11:33:42 AM
Rob, I understand just adding a pair of diodes (and everything else equal) to get a different sound (signal clipped at different point) was the whole point.
Unless I'm misunderstanding.
But if it's ONLY clipping at a different point, it's not a different sound. It's just louder. If that's the only difference, then you can just increase the input level and it'll sound the same.
Maybe louder is reason enough for some designers.
But I want to learn if the sound changes in any way besides the clipping voltage. And as Rob explains, it seems that the amount of clean blend has a noticeable effect!
Quote from: Rob Strand on February 12, 2023, 06:34:38 AM
It can be a bit of an illusion due to adding different amounts of clean!
If you plot the voltage across the 4xdiode/2 and the voltage across the 2xdiodes you get an identical waveform meaning the diode part is doing the same thing except double the voltage.
From that we know if we double the output of the 2xdiodes, that the diode voltages must agree with the 4xdiode. The theory is the 2xdiodes case has one clean blended, and the 4xdiodes has one clean blended. If we double the 2xdiode output signal we get 2xdiode + 2xclean blended, and if we then subtract one clean we expect it should match the 4xdiode+one clean blend.
Wow, it really was an illusion! I replicated your idea, and you're right: the signals look identical if you mix in an inverted clean signal to cancel it out.
So I it seems the only differences are output level and ratio of clean blend.
But I have to wonder, how does the different versions
feel once they are level-matched? Does the lower ratio of clean signal feel like a different knee into clipping? Or does it just feel like there's more overtones? I guess I need to breadboard these to compare...
QuoteBut if it's ONLY clipping at a different point, it's not a different sound. It's just louder. If that's the only difference, then you can just increase the input level and it'll sound the same.
Maybe louder is reason enough for some designers.
But I want to learn if the sound changes in any way besides the clipping voltage. And as Rob explains, it seems that the amount of clean blend has a noticeable effect!
You got it, spot on!
An interesting experiment is to go the other way, ie. have more clean. As a thought experiment that would be using half a diode (0.3V clipping). In practice you don't have an exact half a 1N914, you can use a germanium or Schottky but we know they don't sound quite like a 1N914 so it blurs the result. So what I did in the early 90's was place a gain of 2 (or more) before the clipper and use a single pair of 1N914's - IIRC technically need to increase the resistor and decrease the cap to ground for the same diode currents. To me lots of clean with a heavily clipped diode pairs sounds very unnatural.
When you switch through the three cases you can hear a difference. You can also find what amount of clean sounds right to you. From the theory (or spice sims) we know the difference is largely caused by the amount of clean blend.
There's some finer points that with too many diodes and a hot input signal the clipper stage opamp can itself clip, since the swing is the diodes + the input signal.
QuoteBut I have to wonder, how does the different versions feel once they are level-matched?
They sound different that's for sure, but it's subtle. You really need to experiment. Over time I came to like the 4 diodes (2+2). A friend of mine had a TS9, for a few years he loved it, then he got to the point where he was going to bin it. I think I put a 1+2 diode clipper in there and he was happy with it ever since. The point is it's a subtle thing and it can take time to work out what point suits you.
Quote
Does the lower ratio of clean signal feel like a different knee into clipping? Or does it just feel like there's more overtones? I guess I need to breadboard these to compare..
Yes, you need to do the experiment. If you are someone who likes to ride the clean/overdrive point with how hard you hit the strings etc, you will find one of the diode combinations just seems to work better, kind of a more natural transition. For more cranked settings less clean is better (I think that's another reason I like 2+2 diodes, usable over a wider range of overdrive settings). After hundred of hours playing with these things that's about the only things I can say ... that's life with overdrive pedals. Then there's using different diodes ...
With an opamp that has an infinite treshold, the higher the diode treshold the more the sound will be distortion rather than overdrive. For all the reasons mentioned.
Asymmetrical set up does add some gradual clipping.
Quote from: Steben on February 13, 2023, 01:38:20 AM
With an opamp that has an infinite treshold, the higher the diode treshold the more the sound will be distortion rather than overdrive. For all the reasons mentioned.
Asymmetrical set up does add some gradual clipping.
But do you consider diodes in feedback of an inverting opamp stage just a distortion like diodes to ground? (Inverting stage does not have that +1.)
Its' been a long time since I experimented with opamps and clipping, but I remember even inverting stages with diodes in feedback to sound a bit different from just diodes to ground after the stage. It also might be that my circuits using those were just too different in other ways.
A very simple answer to the original question: more dynamics. When the clipping threshold is low, the resulting sound is more likely to hit the ceiling most of the time; the principal reason why people describe the TS-9 as sounding "compressed", When the clipping threshold is raised by some means (and more diodes in series, or use of diodes with higher forward voltage, is a common strategy) nuances in pick attack produce more graduated degrees of clipping. Yes, you CAN do this with a simple 1+1 diode pair as well. Heck, you could even stick a pair of Schottky diodes in a TS and do it. But the degree of restraint and fine motor control required of the player to achieve nuanced clipping in that context is well beyond the majority of players. The easiest situation is to simply raise the threshold via diodes, so that the player's wrist can do what it does without having to think too much about it.
A second aspect is that creating more gain, in a clipping stage that uses more diodes, allows for use of tonestacks that introduce passive signal loss, without having to add gain 'makeup' stages to compensate.
Quote from: Elektrojänis on February 13, 2023, 04:37:03 AM
Quote from: Steben on February 13, 2023, 01:38:20 AM
With an opamp that has an infinite treshold, the higher the diode treshold the more the sound will be distortion rather than overdrive. For all the reasons mentioned.
Asymmetrical set up does add some gradual clipping.
But do you consider diodes in feedback of an inverting opamp stage just a distortion like diodes to ground? (Inverting stage does not have that +1.)
Its' been a long time since I experimented with opamps and clipping, but I remember even inverting stages with diodes in feedback to sound a bit different from just diodes to ground after the stage. It also might be that my circuits using those were just too different in other ways.
Of course they sound different. With diodes to ground the opamp clips itself. The differences are subtle though. Especially with same EQ design.
QuoteFor a non-inverting clipper the clean signal leaks through with a gain of 1.
Sigh. Here we go again with the "clean blend" idea.
Now that you have the SPICE, input the circuit triangular waveform. The linear ramping up or downwards is plotted in output as the transfer curve of that
distortion circuit.
I bet you get a "folding" curve, a "piece wise" transfer function, where the waveform ramps up in steep fashion at input levels below diode threshold, and in less steep fashion ("unity gain") above the diode threshold.
If a completely straight curve in output is a linear, distortionless, "clean" output, then does that "folded" curve look like a straight curve to you? That's a rhetorical question...
Next, plot the harmonic spectrum with a sine wave input. If a distortionless, "clean" signal shows only a single, "fundamental" harmonic does the folding transfer curve produce that? Another rhetoric question....
If by definition amplitude distortion introduces harmonics to the waveform not present in the input signal then what do you think happens when you "blend" harmonics to fundamental frequency or "clean signal"? Another rhetoric question.
Could we please bury this fallacious concept already?
Quote from: teemuk on February 15, 2023, 10:06:48 AM
Could we please bury this fallacious concept already?
Thank you.
It often seems like quantum mechanics and string theory are better understood than diode clipping by many in the guitar pedal community.
We can spend all day trying to be 100% accurate on this stuff. But if something SOUNDS like a dry blend, and the end goal is SOUND, I see no reason we can't call it that for convenience. Sure, you can say that the "clean" blend on all effects is fake, because once you add some effect signal it's no longer clean. But it sure does sound like mixing between clean and effect, and at the end of the day that's all I care about.
This is a DIY site, not an advanced audio engineering forum. Thus, MANY people here aren't as committed to the deep level of learning required to FULLY understand things like the non-linear behaviors of certain components. For most all applications, that level of knowledge just isn't required to 'do the thing', which is to make good-sounding pedals, mods, and maybe hash together some stuff of your own. Some people simply don't have the time in their lives to take that journey, esp on their own with no formal education behind them. Some might just have poor math skills, a young family, a busy job... :) It's learn as you go for very many.
It's great when those who DO have that much depth behind them try to share and increase understanding. TEACHING is very appreciated. It's great when someone explores a topic, and presents something that us lesser-informed hobbyists otherwise would never read about!
Analogy: Rather than saying "so many in the beginning guitar community" simply lack the understanding to achieve a certain end, I personally prefer to try to show the one with the question how to do something, or at least send them to some resources that might help them grow. Can't build your own arpeggios if you don't know what scales are, or positions over the neck, y'know. They don't care what I know (often it goes right over their head for lack of context), they want an answer to their problem put in a way they can understand.
My 2 cents, YMMV.
Quote from: Steben on February 15, 2023, 01:32:51 AM
Of course they sound different. With diodes to ground the opamp clips itself. The differences are subtle though. Especially with same EQ design.
The op-amp CAN clip, itself, if the voltage swing of the chip is exceeded. Granted, it doesn't take a *lot* of gain to accomplish that, but there is still some room between the point where a diode pair to ground on the output might begin to clip, and the point where what it begins to receive from the op-amp is already clipped.
For instance, if one had a pair of germanium diodes to ground on the output, they would begin to clip when the op-amp output started to hit around +/-300mv. The voltage swing of the op-amp, using a 9V supply, would be around +/-3500mv. So, unless the pickups were especially hot, given typical pickup output, one could apply a gain of around 10-20x in the op-amp, before one started to get clipping within the op-amp and reclipping via the diodes. Of course, given that most op-amp-based overdrives and distortions are going to apply a lot more than a gain of 20x (e.g., the humble MXR Distortion+ is 213x gain at max), the zone between when there is ONLY diode clipping and when there is double-clipping is not all that big; say, the zone between 7:00 and 8:30 on the Gain/Drive control. But I wanted to note that it DOES exist.
QuoteIt often seems like quantum mechanics and string theory are better understood than diode clipping by many in the guitar pedal community.
Quantum mechanics and string theory are only attempted by professionals so the majority of opinions come from professional and scientific people. Even if they turn out to be wrong at least their approach is scientific, and more so, they can see and admit the error of their ways.
Audio is full of quacks and opinions, probably only the top 10% of people in the field actually understand how to apply a scientific approach at all. A significant fraction just reiterate crap they read and they have no idea of the concepts behind it or how to *prove* the result themselves.
Quote from: Rob Strand on February 15, 2023, 09:25:12 PM
Audio is full of quacks and opinions, probably only the top 10% of people in the field actually understand how to apply a scientific approach at all. A significant fraction just reiterate crap they read and they have no idea of the concepts behind it or how to *prove* the result themselves.
Of note, amp manufacturers, who recycle old designs...which were not meant to be overdriven, but their legacy structure makes them prone to blocking distortion and other issues because their 'designers' have no clue what's ACTUALLY going on inside, how the amp will be used - they just copied them. Big bypass and coupling caps, no grid stoppers and so on. This is at the level of multi-million dollar corporations.
The 'complaint' is absolutely valid, hands down. But IMO wrong time/place, is all. I commented because I was concerned that the OP would take the 'general complaint' to be directed at him and his question/conclusions, which are totally appropriate for where he is right now.
QuoteThis is at the level of multi-million dollar corporations.
I suspect they hire people that talk the audio talk. My uncle had a $6k amplifier with silver this and that. It had low voltage fuses on the 1kV/800V rail. Oddly it would blow fuses all the time and in one instance the fuses blew but it started a perpetual arc in the enclosed chassis area which totally blackened the innards.
QuoteI commented because I was concerned that the OP would take the 'general complaint' to be directed at him and his question/conclusions, which are totally appropriate for where he is right now.
Definitely not.
This example shows the non-inverting clipper is a clean blend using the frequency domain.
The level of distortion is the same in both circuit but the level of clean of the non-inverting circuit
is exactly 1V (in peak voltage units) higher than the inverting clipper. The non-inverting clipper
is adding the clean signal to the distorted signal ie. it is a clean blend!
Schematic
(https://i.postimg.cc/gXxkbxTf/ni-clipper-clean-blend-2-schematics.png) (https://postimg.cc/gXxkbxTf)
FFT in usual dB RMS volts
(https://i.postimg.cc/fk0TH0Xd/ni-clipper-clean-blend-2-FFT-units-d-B-RMS.png) (https://postimg.cc/fk0TH0Xd)
FFT in peak voltage units
In LTspice the schematics use peak voltage but the FFTs are displayed in RMS. For this reason the FFT values need to be multiplied by sqrt(2) to convert rms volts to peak volts. You can see this is correct as the input level of the sine wave is 1V (peak) on the schematic and 1V (peak) on the scaled FFT.
(https://i.postimg.cc/dLPQgtmx/ni-clipper-clean-blend-2-FFT-units-peak-voltage.png) (https://postimg.cc/dLPQgtmx)
"Both circuits produce the same level of distortion"
FFT showing additional harmonics of distortion up to 12th....And you still keep calling it a clean blend? :icon_rolleyes:
Why not also post the transfer curve to show how it "folds", like I described, and is nothing but linear. Tubes and even diodes have similar "knee'd" transfer curves, are they "clean blending" too when clipping?
Fit a series resistor to diode chain in an inverting amp. Make it so that you get "unity gain" once diodes conduct. Is this now a "clean blend" (hint: it does exactly the same thing as the non-inverting circuit).
Quote"Both circuits produce the same level of distortion"
FFT showing additional harmonics of distortion up to 12th....And you still keep calling it a clean blend? :icon_rolleyes:
I don't know how you can be so smug with your opinion when it's a simple matter of addition of two signals in the circuit domain. I think most 1st year Engineering students would get the idea of the addition of two signals, whatever those signals are.
If I increase the input level to 2V peak the only thing that differs in the spectra is the level of the fundamental. The clean signal component is effectively passing through and adding to the distorted signal.
(https://i.postimg.cc/gxPg3GLQ/ni-clipper-clean-blend-2-2-V-pk-in-schematics.png) (https://postimg.cc/gxPg3GLQ)
(https://i.postimg.cc/QFk0bvpt/ni-clipper-clean-blend-2-2-Vpk-in-FFT-units-peak-voltage.png) (https://postimg.cc/QFk0bvpt)
I've given three pieces of evidence that supports the idea that the non-inverting clipper blends the clean input with the distorted signal.
What evidence can you provide that contradicts that?
Quote from: Rob Strand on February 16, 2023, 04:25:24 PM
. . . . clipper blends the clean input with the distorted signal.
I think that what you are saying here can be explained by considering the forward slope characteristics of a typical diode.
By this I mean that we are dealing here with real world diodes rather than ideal diodes and these have a exponential type of 'knee' followed by a slope that is begins to approach a more a linear shape. The effective resistance of this slope in combination with the other feedback components provides some forward gain for the clean signal. This appears as a rounding of top of the resultant clipped wave and increases the relative level of the clean signal (or the fundamental in the case of a simple sine wave) to the harmonics and intermodulation products produced by the clipping of the diode.
Although the following is not for soft clipping diode configuration, the principles are similar.
(https://i.postimg.cc/5XM9g10z/Diode-Clipping-Harmonics.png) (https://postimg.cc/5XM9g10z)
QuoteI think that what you are saying here can be explained by considering the forward slope characteristics of a typical diode.
By this I mean that we are dealing here with real world diodes rather than ideal diodes and these have a exponential type of 'knee' followed by a slope that is begins to approach a more a linear shape. The effective resistance of this slope in combination with the other feedback components provides some forward gain for the clean signal. This appears as a rounding of top of the resultant clipped wave and increases the relative level of the clean signal (or the fundamental in the case of a simple sine wave) to the harmonics and intermodulation products produced by the clipping of the diode.
No I'm saying more than that. I'm saying the non-inverting feedback configuration always adds the input signal, regardless if the circuit is non-linear or not.
It's a very basic idea, you don't even care what the blocks are (other than B cannot be a short circuit, or, in practice, A cannot be an open circuit),
(https://i.postimg.cc/2bHMCyGg/Non-inverting-amp-voltage-components.png) (https://postimg.cc/2bHMCyGg)
Quote from: Rob Strand on February 16, 2023, 05:36:24 PM
. . . you don't even care what the blocks are
What about the hypothetical case where A is in fact a pair of 'ideal' diodes.
QuoteWhat about the hypothetical case where A is in fact a pair of 'ideal' diodes.
It still works.
Suppose B passes current IB = Vin / ZB. The voltage across VA is determined by the diode equation, since ID = IB,
ID = IS (exp(VD/(n*Vt)) - 1) ; where Vt = kT/q
It won't take much current before the diode voltage is some defined value.
If B is open then IB = 0 and ID = 0 then the diode will have VD = 0. So it still works.
If you use opamps with BJT input stages you have to expect some deviation from (simple) theory because the input bias currents need to flow through the diodes - it will result in a DC offset at the output.
It's easiest to think of A and B as being passive but they can be linear or non-linear. (I don't want to get off topic with special cases like opamps in A and B.)
You can also build a diode divider. The circuit produces a gain of 2 with essentially no distortion,
(https://i.postimg.cc/LqgqMQSp/diode-divider-gain-of-2.png) (https://postimg.cc/LqgqMQSp)
QuoteWhat evidence can you provide that contradicts that?
Plot the transfer function. It is not straight line but two lines, "folding". Even the very lack of overall linearity should point out that this circuit will amplitude distort the signal.
I have explained how the gain "folding" to a decreased ratio - (in this circuits case to unity gain) - creates amplitude distortion. The same explanation demonstrates that, other than below diode Vf, you do not get a clean output signal from this circuit. It is an impossibility.
There is no "clean blending" anywhere; different parts of the waveform are just being amplified by different gain ratios.
I have stated the rudimentary fact that "clean" signal contains no extraneous harmonics and that a signal is distorted if it does. Blending the two is fallacious concept, they can not co-exist, and "clean blend to distortion" is an oxymoron. Even your FFT plot shows a great deal of these extraneous harmonics.
Now it is your turn to show evidence of the contrary. IMO, the OP came hear to learn and you shouldn't confuse him with false theories even though you happen to hold dear this "clean blend" concept.
All you have done it reiterate the same words with no quantitative results.
QuoteEven the very lack of overall linearity should point out that this circuit will amplitude distort the signal.
It's not the fact it distorts that's in question. Both the non-inverting and inverting forms distort. The point is the difference between the two outputs *is* the input signal, which is clean.
QuoteThere is no "clean blending" anywhere; different parts of the waveform are just being amplified by different gain ratios
This alone shows the output signal is the sum of two components, one of them clean.
(https://i.postimg.cc/2bHMCyGg/Non-inverting-amp-voltage-components.png) (https://postimg.cc/2bHMCyGg)
QuoteI have stated the rudimentary fact that "clean" signal contains no extraneous harmonics and that a signal is distorted if it does. Blending the two is fallacious concept, they can not co-exist, and "clean blend to distortion" is an oxymoron. Even your FFT plot shows a great deal of these extraneous harmonics.
Well I can take a distorted signal and add it to a clean signal. It is a simple process of mixing. You can buy pedals that do it.
The point is the non-inverting form does this mixing by nature.
QuoteEven your FFT plot shows a great deal of these extraneous harmonics.
They are not extraneous they *are* the distorted signal. The whole point was to make the harmonics the same in the two circuits.
The only difference between the non-inverting and inverting forms *is* the fundamental. In the last example 2V of fundamental is there in plain sight.
QuoteNow it is your turn to show evidence of the contrary. IMO, the OP came hear to learn and you shouldn't confuse him with false theories even though you happen to hold dear this "clean blend" concept.
What's wrong is your concept of clean *blending* altogether. By definition it is adding a clean signal to a distorted signal.
There's a difference between theories and a demonstration. Theories are only of use if they explain an observation. I've provided a number of demonstrations where it's clear the observation is the the clean signal adds to the distorted signal. You have provided no demonstrations at all.
(https://i.postimg.cc/Z90Zb4cB/ni-clipper-clean-blend-hard-clipping-variable-input.png) (https://postimg.cc/Z90Zb4cB)
The theory that is explains the observations is this,
(https://i.postimg.cc/2bHMCyGg/Non-inverting-amp-voltage-components.png) (https://postimg.cc/2bHMCyGg)
Quote from: teemuk on February 16, 2023, 11:23:30 PM
they can not co-exist, and "clean blend to distortion" is an oxymoron
Now I'm intrigued to find out what you mean.
(https://i.postimg.cc/bZMGQG8k/blend.jpg) (https://postimg.cc/bZMGQG8k)
You guys familiar with dualities (https://en.wikipedia.org/wiki/Duality_(mathematics))? Or maybe you're not even arguing two equivalent models but about the particular words to describe one.
QuoteIMO, the OP came hear to learn and you shouldn't confuse him
Perhaps a thread split is in order.
Quote from: FiveseveN on February 17, 2023, 04:18:43 AM
Perhaps a thread split is in order.
With thermionic gas diodes inside the NFB loop... :icon_wink:
Rob is right, in a non-inverting clipper the original signal is effectively blended (summed) with a pure clipped signal, ala:
(https://i.postimg.cc/YGnVQMyG/IMG-20230208-171919394.jpg) (https://postimg.cc/YGnVQMyG)
Quote from: merlinb on February 17, 2023, 04:52:35 AM
Rob is right, in a non-inverting clipper the original signal is effectively blended (summed) with a pure clipped signal, ala:
(https://i.postimg.cc/YGnVQMyG/IMG-20230208-171919394.jpg) (https://postimg.cc/YGnVQMyG)
This is also what happens when resistance is added in series to hard clipping diodes or naturally with the various forward transfer slopes of different diodes. This is what makes the difference in sound between Schottky, germanium. silicon, gallium arsenide (LED) and so on.
Quote from: FiveseveN on February 17, 2023, 04:18:43 AM
Perhaps a thread split is in order.
What Rob posted above makes a lot of sense regarding the case of the non-inverting soft clipping op amp stage.
I would personally welcome a sensible discussion regarding the many aspects of diode clipping that get overlooked or taken for granted.
One example is just how diode clipping actually produces a 'fuzz' sound as just the effect of adding harmonics to a single tone is inconsistent with the sound or spectral content of fuzz.
Virtually everything that has been written in the pedal community avoids discussing this in favour of just showing simple clipped sine waves.
Let's get some things straight, here:
1) Guitar signals, produced by picking/plucking/strumming a string, are dynamic. This means their amplitude changes over time (generally very quickly, unless artificially held constant), and their inherent harmonic content changes over time. Any additional harmonic content produced by a circuit is ultimately a function of what that circuit is fed, and what it is fed changes quickly. In short, a guitar string is not a signal generator, producing a waveform of constant shape and amplitude.
2) Let us distinguish between what is sent to our ears, and what we perceive. I keep harping on about "auditory scene analysis", but I'm dead serious about it. Here's a nice, profusely illustrated, explanation/summary of what it means: https://www.phon.ucl.ac.uk/courses/spsci/AUDL4007/Scene_analysis.pdf Since we actively (though generally unconsciously) "group" auditory content, and since the harmonic content produced by feeding a guitar signal into any sort of clipping circuit will change over time, and generally much faster than the note fundamental does, we are likely to mentally group that auditory content into the basic string signal and "other stuff". In other words, unless the added harmonic content and original signal last the same length of time and at similar levels, we will "hear" them separately, the same way you are currently "hearing" various differentiable sound sources (as well as seeing different letters and screen windows), even though it's all landing on two hapless eardrums.
Do not confuse what is on a scope screen with how you perceive sound.
Quote from: Mark Hammer on February 17, 2023, 07:01:01 AM
Let's get some things straight, here: . . . .
Exactly -
This is why I solicited a discussion on clipping beyond the simple view of clipped sinewaves that everyone seems to write about on virtually everything I have seen on the Internet and posted in the pedal community, even from the most respected people like RG and Jack.
The following make for interesting and enlightening reading on this subject.
https://www.gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-8-2-3-pitch-perception.pdf
https://www.gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-8-2-4-partial-grouping.pdf
https://www.gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-8-2-5-inharmonicity.pdf
https://www.gitec-forum-eng.de/wp-content/uploads/2019/02/poteg-10-08-05-distortion-devices.pdf
https://www.gitec-forum-eng.de/wp-content/uploads/2019/02/poteg-10-10-4-distortion-comparison.pdf
https://www.gitec-forum-eng.de/wp-content/uploads/2019/02/poteg-10-10-5-distortion-audibility.pdf
In fact this whole book should be essential reading to anyone involved with guitars, amplifiers and effects pedals:
https://www.gitec-forum-eng.de/the-book/
Quote from: FSFX on February 17, 2023, 07:32:51 AM
In fact this whole book should be essential reading to anyone involved with guitars, amplifiers and effects pedals:
https://www.gitec-forum-eng.de/the-book/
From above mentioned book.. :icon_wink:
(page 10-235)
(https://i.imgur.com/sh5CWb0.png)
Quote from: merlinb on February 17, 2023, 04:52:35 AM
Rob is right, in a non-inverting clipper the original signal is effectively blended (summed) with a pure clipped signal, ala:
(https://i.postimg.cc/YGnVQMyG/IMG-20230208-171919394.jpg) (https://postimg.cc/YGnVQMyG)
I don't see the "original signal" in the output. I see a severily distorted signal that just partially conveys some elements of waveform of the "original signal". (The part folding to unity gain
Edit: and the "vertical" part, part amplified with high gain).
Let's flip this around, let's not concentrate on the peak portion. Imagine a brickwall clipped signal, is it - by the above logic - "clean blending original signal" below clipping threshold. No. Way don't say it is.
The "superimposing" is a much more descriptive term of what happens.
Quote from: teemuk on February 17, 2023, 10:25:13 AM
Imagine a brickwall clipped signal, is it - by the above logic - "clean blending original signal" below clipping threshold.
I haven't seen anyone claiming that. Maybe a failure to explain what the "above logic" is, though we've been through it a few times and with different examples.
QuoteLet's flip this around
Yes, let's!
(https://i.postimg.cc/McYHLstB/superpos.jpg) (https://postimg.cc/McYHLstB)
What happens here, do we not get back the clean signal? Where did it come from if it was no longer there?
Superposition is indeed the correct concept but surely you understand that "mixing" or "blending" describe this same thing.
Actually my previous post was maybe a bit misleading in its wording. In practice, that vertical slope of the waveform is amplified linearly, it's just not very evident because of super high gain ratio in proportion to gain ratio of amplifying the peak.
In either case we see virtually same result: peak of the waveform is compressed by significant gain reduction. We hear this as distortion. (Are folks just looking at the pictures and thinking "oh, that part looks clean").
There's really not so much difference whether we compress from gain of 100x to gain of 1x, like Tube Screamer, or from gain of 100x to downright brickwall limit; proportionally the waveform peak still compresses significantly and yes, both sound about as much distorted because of that. Both of those waveforms bear a striking similarity to square wave when a clean signal would be a sinusoid.
No clean signal is heard if you listen signals going through either transfer function.
At lower gain ratios the less steep compression of gain reducing just to unity generates a bit more gradual compression effect but it's still not a clean signal.
In fact, if we talk about this "superimposing" we could also say we have high gain clean superimposed with low gain clean and it still sounds a bit fishy and confusing... The non-linear transfer function where two linear gain curves fold really describes much better how the circuit works. And when we acknowledge that we must also acknowledge that there is very little difference to other nearly similar transfer functions where high gain folds to lower gain.
Quote from: teemuk on February 17, 2023, 12:21:20 PM
Actually my previous post was maybe a bit misleading in its wording.
I am sorry but I find it not just misleading but without merit.
What has been posted by others here is closer to what is actually happening.
The use of the term 'clean signal' does not limit it to a sinusoidal waveform. A plucked string signal into a pedal or even a squarewave may be considered a 'clean signal' as it is the original pre-distorted signal.
There are many other things you say which don't make sense either. Whether this is a lack of understanding or an issue with translation if English is not your native language.
I seriously recommend taking time to read through a lot of the GITEC forum book that I posted a link to before as it is written by a physics professor with an interest in music so he has provided great insight into the whole theory underpinning the subject that this forum is dedicated to.
Another university professor that publishes many in-depth YouTube videos about the whole world of the electronics behind music technology is Aaron Lanterman.
I recommend people to explore some of his fine lectures on YouTube.
https://www.youtube.com/user/abovenyquist
Quote from: antonis on February 17, 2023, 08:45:54 AM
Quote from: FSFX on February 17, 2023, 07:32:51 AM
In fact this whole book should be essential reading to anyone involved with guitars, amplifiers and effects pedals:
https://www.gitec-forum-eng.de/the-book/
From above mentioned book.. :icon_wink:
(page 10-235)
More interesting the paragraph with the blue markup answers this thread, especially the part after the blue marked-up text.
My point is this stuff shouldn't have to come from a book (or me). You should be able to work it out from basic electronics. That's why I like Physicists you just tell them how an op amp works and they can work out the rest.
Quote from: Rob Strand on February 17, 2023, 04:22:34 PM
... That's why I like Physicists you just tell them how an op amp works and they can work out the rest.
But only point-shaped ideal opamps in a vacuum =)
Bias currents, DC offsets, etc. are dirty things reserved for lowly engineers.
QuoteBias currents, DC offsets, etc. are dirty things reserved for lowly engineers.
True, but if you add that to the model the physicists will get it. I think a lot of engineers don't get it either.
For heat flow engineering you might find physicists starting on the wrong foot. They would use differential equations but the engineers would look up the correlation equations in a book with answer already there. These days people use FEM on computers, which is the physicist's method under the hood.
if something looks and quacks like a duck, surely we can call it a duck?
i tried cancelling out the dry signal from a non-inverting clipper, and compared it to an inverting clipper. they're indistinguishable with a variety of waveforms (triangle, square, saw):
(https://i.postimg.cc/6TNw7XsQ/diode-softclip-test-cleanmix-2-20230219-screenshot.png) (https://postimg.cc/6TNw7XsQ)
some very interesting reading in this thread!! but i'd like to bring things back to something a little more practical...
increasing the forward voltage of diodes in the feedback loop (either by stacking them or by using LEDs, etc) does two things: it increases the output level of the distortion, and it (as a result) decreases the relative volume of the "dry" signal (i'll say "dry" since "clean" has gotten such a bad name).
if we want no "dry" signal at all, we can use the inverting configuration. in that case, if we use the other half of an opamp to re-invert the distortion output, we can even use that inverting amp to mix in a specific amount of the "dry" signal!
i guess the only drawback is it becomes harder to implement filters without impedance issues? maybe it's no issue. i haven't yet tried an inverting version of the timmy, but now i'm curious...
You are on the right track with everything. Cancelling is generally a little haphazard. If you look at reply #7 I've got a non-inverting form that blends. It's just a series resistor (Circuit 2, R19 4k7). To kill the blend on that one, just short out the resistor and it's back to the inverting non-blending ckt. Also have the option of small resistor = less blend. FWIW, Marshall Blues Breaker pedal uses the non-inverting form with blend (6k8).