Importance of IV knee graph of a Diode in soft clipping applications

[Vivek]

From all above

and from that famous old article

https://web.archive.org/web/20190831161652/http://www.bteaudio.com/articles/TSS/TSS.html

I understood : The output waveform of the noninverting clipper consists of two components:
(1) the amplified and clipped version of the input waveform
(2) plus the unamplified input waveform.


I also feel compliance resistors allow part of original signal to go through


My question is

What is the difference between :

A) noninverting clipper with no compliance resistors
and
B) Inverting clipper with compliance resistors in series with the diodes

[iainpunk]

My question is

What is the difference between :

A) noninverting clipper with no compliance resistors
and
B) Inverting clipper with compliance resistors in series with the diodes

they can sound exactly the same, but the inverting stage can clip hard, and the non inverting stage can't.
the systems both respond differently to capacitor tone shaping,
the inverting one can go down to -inf dB where the non inverting can only go down to 0dB
i prefer noninverting due to easier math... you can throw almost anything in the nfb loop, calculate the response and mirror it around the 0db axis. the math is harder with inverting stages imho.

cheers, Iain

[Vivek]

I for one like diodes in the NFB path of an inverting opamps better than a non inverting because I find it easier to tune the clipping characteristics.

i prefer noninverting due to easier math. imho.

cheers, Iain

I'm lost !!!!!!

[iainpunk]

its both valid, and up to personal preference,
he prefers noninv. for tuning the specific clipping sounds, like knee and hardness.
i prefer inv. for easier tuning the freq. response, and i care less (not at all) about the specifics of clipping, like knee and hardness.
i think his method is more usefull for you, since it allows for really fine tuning and perfecting the clipping itself.

cheers

[Fancy Lime]

Hmm, funny. I find inverting stages easier math-wise. Well, neither kind is rocket surgery. But for me, the ability to go below 0db is often useful when cramming filter functionality into clipping stages. One big caveat, though: if you want now noise and high input impedance, you need a non-inverting opamps stage. So the very first stage should usually be non-inverting to lift the signal out of the noise floor. For an amp in a box, I would make the first stage something similar to a tube screamer but with a higher corner frequency, maybe 1.5kHz, LEDs, possibly asymmetrical, and probably a bit less gain. Next a bass control and maybe mid control, then an inverting clipping stage and after that the treble control. At the very end I would stick a very primitive pseudo-speakersim in the form of a two to four pole Butterworth(ish) low pass filter at somewhere around 6kHz ( adjust to taste). Remember, this is just where I personally would start tinkering but there is more than one way to pickle a herring. You do you! We'll TRY to help, of course, but reading my own text here I wonder if that is really all that helpful...

Cheers,
Andy

[Steben]

I for one like diodes in the NFB path of an inverting opamps better than a non inverting because I find it easier to tune the clipping characteristics.

i prefer noninverting due to easier math. imho.

cheers, Iain

I'm lost !!!!!!

There is no spoon mate

[Fancy Lime]

I for one like diodes in the NFB path of an inverting opamps better than a non inverting because I find it easier to tune the clipping characteristics.

i prefer noninverting due to easier math. imho.

cheers, Iain

I'm lost !!!!!!

There is no spoon mate

True!

I thought some more about my and Ian's different perceptions on this.  I think, which is easier depends on whether you think in volts or in amperes. Non-inverting is easier to reason about in voltages whereas inverting is easy in current. As long as there are only resistors involved, that does not make a real difference. But with diodes, one or the other may be easier to wrap your head around, depending on how you are wired.

Cheers,
Andy

[iainpunk]

Hmm, funny. I find inverting stages easier math-wise.

well, i think when you use 'hard number math' its kinda equal, but when you are in to 'freestyle-interpretive math' non-inverting is easier because you can just ''flip over'' the response of what you put in the feedback loop.
put a mid scoop in the NFB? you get a mid boost and the frequency's above and below that still have a gain of 1!
put in crossover diodes? you get clipping!
put in clipping? you get gating! *
put in a mid boost? you get a mid scoop!
dislike the big muff midscoop, but like the functionality? put it in a NFB!!!!!!! **
the only thing you have to keep in mind is phase margins and such, but phase margins also apply to inverting stages.

But for me, the ability to go below 0db is often useful when cramming filter functionality into clipping stages.

you can as well in a non inverting gain stage, but it needs another active element to get that to work, and the phase margins may become a bit sketchy...

Remember, this is just where I personally would start tinkering but there is more than one way to pickle a herring. You do you! We'll TRY to help, of course, but reading my own text here I wonder if that is really all that helpful...

this is exactly the message Vivek needs to hear.

cheers, Iain

* not clean gating, but what i'd like to call ''soft dirty gating'' the gain under the threshold is 1 and there is crossover distortion at play.
** make sure that the pot's range is limited on the treble boost side, use a 5k6 resistor with a 100k pot. this keeps the treble boost shelved. omitting the resistor makes the op amp try to boost the high frequency's WAY to much (near infinite)

[Vivek]

Thanks everyone

Learnt a lot from this thread, and still learning !!!

[iainpunk]

Thanks everyone

Learnt a lot from this thread, and still learning !!!

you're welcome! i enjoy these kinds of threads the most tbh. low pressure and just throwing up some ideas, opinions and thoughts.

cheers, Iain