What was the problem with my solution:
"You need a threshold after a differentiator as well as a threshold before the differentiator - just need to recognise a near-zero differential coupled to a DC offset for a certain length of time."
?
Do you mean something like a built in null tester?
I believe that's also how the SMD "Amp Dyno" does it...
I realize there are analog solutions to my project I just don't know how to build them. I'm not sure what a differentiation circuit after a threshold circuit does or how to test if a near zero differential between to circuits has occurred over a period of time with analog stuffs? please elaborate if you don't mind on how this is done, keeping in mind I only have the single output from the previous piece of equipment, I don't know what the signal going into that piece of equipment looks like. If I did I could easily setup a comparator to just watch the two signals and amplifier the difference and voila, with some tweaking of course. I'm curious if you can point me to some examples of what you speak of? Thanks
A differentiator is a standard opamp circuit, easy to find this on the web.
Threshold detection is done with comparators, here a pair of comparators forming a window comparator could be used to detect when the signal's absolute value is larger than some threshold voltage, another to detect when the differentiated signal's absolute value is below some threshold.
The times when the signal isn't close to zero but the differentiated version is close to zero are the interesting points - as this will be true at clipping for non-trivial lengths of time - signal has zero slope, but itsn't zero itself.
Then you have to do some decision logic about how long and how frequently this condition
holds to ensure false detection is minimized.
You'd need the window comparator circuit anyway to detect clipping the normal way, so there will be examples of that out there.
Threshold detection is done with comparators, here a pair of comparators forming a window comparator could be used to detect when the signal's absolute value is larger than some threshold voltage, another to detect when the differentiated signal's absolute value is below some threshold.
The times when the signal isn't close to zero but the differentiated version is close to zero are the interesting points - as this will be true at clipping for non-trivial lengths of time - signal has zero slope, but itsn't zero itself.
Then you have to do some decision logic about how long and how frequently this condition
holds to ensure false detection is minimized.
You'd need the window comparator circuit anyway to detect clipping the normal way, so there will be examples of that out there.
Yep, I'm with you now, I found a patent (US 8 712 066B1) for just such a circuit and it's starting to make sense. Thank you very much
Clipping detection is accurate and straight forward if it's integrated into the amplifier, not hung on the outside. When an amp clips the global feedback amplitude jumps and this is easy to detect. You need a detector for both polarities. You can hang a detector across the differential input since the undistorted signal there approaches zero. But this risks loading problems. Just like output protection, it's only a problem if you are after super low distortion. Detecting the output approaching the rail is a good but not great strategy since it does not detect amp shorts and overloads.