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Headphone amplifier power spec distortion cut-off

restorer-john

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...introducing clipping to a test waveform...

I don't think anyone was talking about 'introducing' amplifier clipping to a recorded waveform were they? That is not possible.

Clipping is a dynamic, signal driven consequence and has characteristics that are often quite unique. Clipping behavior is fascinating to see. Many 'highly regarded' amplifiers collapse into uncontrolled oscillators or simply can't recover in a reasonable time from certain clipping events.

I can screen grab some clipping events on my DSO if it is interesting to people here.
 

restorer-john

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I find it ironic that we need plugins to 'add' distortion, to see if we can hear it. LOL. We've come so far and distortion is so low, we've forgotten what it sounds like... :)

Go hard and get this:

https://www.waves.com/plugins/abbey-road-vinyl#presenting-the-abbey-road-vinyl-plugin

abbey road.JPG
 

DonH56

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I don't think anyone was talking about 'introducing' amplifier clipping to a recorded waveform were they? That is not possible.

Clipping is a dynamic, signal driven consequence and has characteristics that are often quite unique. Clipping behavior is fascinating to see. Many 'highly regarded' amplifiers collapse into uncontrolled oscillators or simply can't recover in a reasonable time from certain clipping events.

I can screen grab some clipping events on my DSO if it is interesting to people here.

I thought that was your objection to just adding a fixed amount of distortion? That it was not actually clipping? I agree, just noted that I have added clipping, in the strict theoretical sense, to waveforms by cutting them off ("flat-topping"). Easy to do in the digital age by processing (manipulating ;) ) the data.

But not the same as real amplifier clipping, just a technique to let folk hear what clipping might sound like sans all the other badness. As for amplifier misbehaviour during clipping, completely agree. And screen shots would be awesome.
 

restorer-john

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...just a technique to let folk hear what clipping might sound like sans all the other badness...

Agreed, as long the frequencies are low enough to convey the multiple harmonics caused by the 'faux'* clipping. In music, it would interesting to compare the sound of 'faux' clipping to an unconditionally stable amplifier at the onset of actual clipping. (No, I don't spend my weekends having a few drinks and listening to various amps clipping if that's what you guys thought. :) )

The lovely little depictions of nice clean flat topping amplifiers are seldom (if ever) seen. It's usually a power supply modulated, multi trace mess, that wobbles up and down and generally looks horrible.

* digitally manipulated clip to include harmonics?
 
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amirm

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I can screen grab some clipping events on my DSO if it is interesting to people here.
I captured a few from AVRs I had on hand for another discussion a few of years back:

Pioneer (class D) AVR:

Pioneer AVR Clipping.png


This is I think is the same AVR but before severe clipping:

p20mclip2.png


This I think was an Onkyo AVR under severe clipping:

Onkyo AVR CLipping.png


This is a Yamaha AVR barely clipping in one channel:

Yamaha AVR Clipping.png


The interactions are quite complex and have to do with feedback circuit, protection circuit, sagging of the power supply rails, current limiting, oscillation, etc.
 

restorer-john

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Most HiFi magazines tested 'at the onset of visible waveform clipping' or words to that effect.

That is how I have always tested as well. It is a repeatable and easily demonstrated limiting point and can be accompanied with the visual depiction. Obviously, at the point of waveform clipping Amir's AP is going to go virtually vertical on the THD vs output voltage plot just as I have to quickly switch ranges on an analog meter or watch the harmonic 'spray' on an FFT.

The onset of clipping test isn't hard to do and anyone with a decent scope, a few loads, a signal source and a judicious hand can get very accurate results for power output. That would mean plenty of other members could contribute comparable tests for other headphone amps for comparison purposes.

With analog amplifiers, it is not as black and white like hitting 0dBFS on a DAC where spikes appear and disappear within a fraction of a dB of level change.

I'd like to see the AP's plot of THD vs output voltage/power and a onset of clipping DSO/CRO scope shot with AC RMS scales. Headphone amps are no different to normal amplifiers and I can't see why all the normal traditional tests can't be applied to them also. So there is single and both channels driven (to show PSU regulation effects) and dynamic tests too. All the others are pretty much already covered.
 

DonH56

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The caveat has "always" been how you define the onset of clipping. The knee ranges from very soft (e.g. old tube amp) to very sharp (e.g. SS amp with lots of feedback). The 1% choice is a reasonable compromise IMO. And yah seeing the actual curve and the output during clipping is priceless.

Hey Amir, when ya' gotta' save up enough to buy the active loadbox? :)
 
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amirm

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Hey Amir, when ya' gotta' save up enough to buy the active loadbox? :)
I got stickshock when I looked at how much Audio Precision charges for it a while back. :)
 
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