What would happen if...

[Mark Hammer]

...one utilized a different clipping strategy for each half cycle?

Let us say one inserted a single diode in the feedback loop of an op-amp, such that only one half-wave was affected, and the other half-wave was allowed to do whatever the gain-setting commanded.  And on the output of said op-amp was a single diode going to ground, oriented such that only the unaffected half-cycle would be clipped.  And let us further assume that the individual diodes have identical forward voltages.

Would this behave or sound any different than what we are used to?  I was reading a thread on another forum, and it occurred to me that I've seen circuits where one pair of diodes is used in the feedback loop, and then another pair is used somewhere after that output, but that simply duplicates clipping on both half-cycles.  And I know some octaving circuits separate half-cycles using phase-splitters and diodes, but they don't process each half-cycle differently.  I don't know that I've ever seen a circuit that treats and clips each half-cycle differently.

I'm off for my 5th Covid shot in 10 minutes, or else I'd do the experiment myself.  But, opinions?

[ElectricDruid]

Theory says that you should get more even harmonics mixed in with your odd harmonics.

Any of these distortion processes are basically "waveshaping" in the synthesiser sense, and there's quite a bit of decent theoretical work done on that. The TLDR version is that distortion functions that are rotationally symmetric produce only odd harmonics, whereas ones that are mirror-symmetric produce only even harmonics. Functions that are not symmetrical in either way produce both in varying amounts. Which is what you're proposing. And also which is the result of the deliberate "mis-biasing" of power amp tubes in a Marshall valve amp - makes the resulting distortion no longer symmetrical and increases even harmonics.

That's a *very* broad-brush answer though. How that actually *sounds* is down to the details of which harmonics exactly and how much and how they evolve over time and so on, which theory isn't going to tell us so easily.

Tom

[idy]

That is what I usually try to do... Although the one I often use is let the opamp itself clip on one half cycle and some MOSFET +diode on the other. I suppose I could add a diode to ground later.

What I hear is you still heat the character of the guitar even as clipping starts, gravel+clarity. Then you hit a hard limit at higher gain and get assymetric but totally clipped, the wave shape is dominated by the clippers.

[CheapPedalCollector]

It would be different and have that tubescreamer "clean" thing in the background.

I'll one up you, how about feedback diode in an inverting configuration and one in a non inverting configuration.

[marcelomd]

You can cascade gain stages that clip only one side of the signal, like this excerpt from Amptweaker's Tight Metal, from Aion FX.

Note three gain stages with zeners, providing assymetric clipping.

[Rob Strand]

With the amount of gain in distortion/overdrive pedals, as soon as you remove one diode the opamp clips.   As soon as that happens the sound of opamp clipping enters the picture.

Would this behave or sound any different than what we are used to?  I was reading a thread on another forum, and it occurred to me that I've seen circuits where one pair of diodes is used in the feedback loop, and then another pair is used somewhere after that output, but that simply duplicates clipping on both half-cycles.

It's not duplication, ithe feedback clipper prevents the opamp from clipping and that means the tone becomes independent of the opamp (unlike say the MXR distortion).

There's nothing *wrong* with single ended clipping.  You can do what you want.   What might not be so obvious is single ended clipping will do different things when feedback or stages are DC coupled vs AC coupled.  Asymmetrical waveforms will charge-up caps to meet the new average DC conditions, which varies depending on the amount of clipping, and there will be a time for that new equilibrium to be reached.

[GGBB]

I'm off for my 5th Covid shot in 10 minutes

Painful! Why wouldn't you just get them periodically like most people? 


I have a modified BluesBreaker circuit that has a clipping switch which changes the feedback clippers from 2||2 to 1||3 using the same 4 diodes. Flipping back and forth there is no noticeable difference between the output volume. But they sound different - distinctly but not massively. This is at lowish/amp-on-the-edge-of-breakup gain levels. No post op-amp clipping here though.

The 1||3 setup is "woollier" in texture - less clarity, slightly warmer and grittier, it doesn't really sound like more clipping overall but naturally it would be more clipping on half of the wave. I would assume that at that low gain level I am not clipping the 3 diode side but I can't be certain (I should scope it I suppose). I do know that there is no op-amp clipping - the switch can also disconnect the diodes and when I do that at the same gain level the signal is clean. I'm not sure if this actually asymmetrical clipping, 2nd order harmonics etc, or single-sided "half-wave" clipping, or something else, but there's a definite difference.

[bluebunny]

I'm off for my 5th Covid shot in 10 minutes

Painful! Why wouldn't you just get them periodically like most people? 

LOL! 

So when they've used both arms and both butt cheeks, where does the fifth shot go??     

[Rob Strand]

So when they've used both arms and both butt cheeks, where does the fifth shot go??

In the unmentionables.

[amptramp]

I have had a situation happen during a radio restoration where a speaker cone was hitting the board the speaker was mounted on, giving a hard clip when the cone moved forward.  One-sided electrical clipping would do the same thing but without having the cone actually hit something.  If you like that sound of cone hitting wood, this is what you will get from one-sided clipping (although the phase may be different - the cone may clip when the speaker pulls the cone back).

Electrical clipping would be softer - after all, the damping factor of the amplifier may be high but will still not be the equivalent of the speaker cone coming to a sudden dead stop.  Electronic clipping will still have some softness since the forward resistance of the diode is low, but not zero, and it approaches that low value gradually (in terms of change during the progress of the waveform).

You have to ask yourself, if you add one-sided clipping, is this going to give you the sound you want?

[bluebunny]

So when they've used both arms and both butt cheeks, where does the fifth shot go??

In the unmentionables.

Ack!  He mentioned it... 

[Mark Hammer]

The important thing is to do all the activities that require reaching up prior to getting the shot.  Or at least putting them off for another 18-24hrs.

[Steben]

Wasn't it crate that used this to mimick tube preamp duty cycle shift etc?
And Carvin SX.... check page 274
https://www.jeanpierrepoulin.com/PDF/transistor.pdf

[Matthew Sanford]

So, soft clip up on the feedback and hard clip down on the output? Would it be clipped more on the negative cycle? Just trying to keep up...

[Dormammu]

Mark Hammer
Quite an odd question for someone with so many posts on this forum.
Some opamps have "notches" (that's what I call them) in the shape of output waveform, when overdriven.
They sound unpleasant to my ears.
Which is not observed when using diodes in the feedback loop.
So if we use the suggested clipping method — we will definitely get different waveforms in different half-waves.

[Rob Strand]

Wasn't it crate that used this to mimick tube preamp duty cycle shift etc?
And Carvin SX.... check page 274

p274, both Carvin and Peavey, are the ones that come to my mind for splitting the polarities.   These are symmetrical, and parallel mixing, as they are emulating the power amp.   Unlike the cascade set-ups which do the second harmonic thing.

For bias shifting and asymmetry the one that comes to my mind actually the Flexwave on p275.  (Pulling one feedback diode is essentially the asymmetrical version.)