why is peak detector circuit not popular?

https://www.allaboutcircuits.com/vol_3/chpt_3/5.html

I mean why is using a peak detector circuit less popular for setting amplifier gains and finding the clipping point of a component? I've spent some time today testing one and it works very well considering it uses a single diode and capacitor. I was able to find almost the exact same point I found when using a 'scope when seeing the clipping point of my head unit, and also setting the gain on my amplifier.

I'm wondering why these are not mentioned more often as a cheaper alternative to using a 'scope. My guess is the technique of setting amplifier voltage based on speaker impedance and using ohm's law is popular, however I find that technique not as strong because it is based off assumptions.

I see the 'scope as the best method, a quasi-scope using a computer and a sound card next best, followed by a peak detector, the finally the voltage and ohm's law technique.

-J

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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.

I'd assume because the root-2 relationship to RMS voltage is known. (Although that RMS is full bandwidth and not tuned.)

But I'm curious, how does that peak detector detect clipping? (Or does it detect the distorted high-freq harmonics?)

Caveat - I can feel another d'oh coming on... but it has been a long day.

It works like this:

Play a sine or sawtooth wave into an amplifier, and connect the circuit on the output. The diode will rectify the AC signal from the amplifier and pass only a series of DC pulses to the capacitor. The capacitor stores the peak value of these pulses, as it has nowhere to discharge to.

The trick is to gradually raise the amplifier gain and measure the DC potential across the capacitor. When the amplifier clips the sine wave input to it, the magnitude of the DC pulses passed to the capacitor will not raise any higher, and the DC potential across the cap will not rise any higher despite increasing the amplifier gain.

Hopefully that makes sense, a picture might be more useful to show how it works. I'll put some more effort into it if this is not clear enough.

-J

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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.

I'm thinking yeah, so, a-ha....
Then the "...will not raise any higher...".

Now I'm thinking d'OH!!


Thanks teenkertoy!
I was thinking of a more "automated" method and couldn't see how the circuit could determine the changed RMS to peak (DC) value. But YOU adjust the RMS and see when the peak stops rising.


Hmmm - a peak to RMS or average comparator - LED lights when average to peak goes above 0.71 (3dB).
Ah yes - a crest factor meter!


BTW - it should be popular. Though manual, it is a once off...
And frequency shouldn't matter - unless clipping is only narrow band...
Not that I'm an expert...!

Yeah that's great and all, but the great thing about the simple peak detector is it's ... simplicity. Two components and a volt meter. Nearly fool proof, doesn't need a breadboard really, and dirt cheap. Easily accessible to the masses and not complicated if I draw a few pictures.

I'm just baffled why this is not more common as a substitute for a scope which is 1) expensive and 2) not easy to use for the average Joe.

-J

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Malcom: "This is the captain. We have a...little problem with our engine sequence, so we may experience some slight turbulence and then...explode."
Jayne: "We're gonna explode? I don't wanna explode.

I agree! A 1uF cap, 1k resistor & a signal diode - under 50c.
And that should be ok for most signals; maybe go to 1nF & 1M for high-impedance if needed.
Change or pot the R for other center frequencies (if relevant).


But how to tell if the other post... er, thread is clipping.... aha! (LOL - ie - amp keeps clipping)