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 26th August 2019, 03:57 AM #11 PRR   diyAudio Member     Join Date: Jun 2003 Location: Maine USA The value of the fundamental of a square wave is not 1.0 but 1.27. That does not cover the discrepancy, but reminds up that wave-smacking is not a simple thing.
Gnobuddy
diyAudio Member

Join Date: Mar 2016
Quote:
 Originally Posted by PRR Total harmonic distortion - Wikipedia
And that link contains the sentence "A pure square wave with infinite harmonics has THDF of 48.3%,[1][13][14]..."

The first of those references is available online, and proved to be readable, at least initially; I was able to follow the calculation of THD for a square wave, and it is {square root of ( ((pi^2)/8) - 1 )}, which works out to 48.3%.

So you are correct, and my estimate is badly wrong.

I think I found the mistake I was making: I calculated THD for a square wave and sine wave of the same peak value, visualizing an amp gradually driven from clean into clipping.

But if you take the Fourier series of a square wave, the amplitude of the fundamental is not the same as the amplitude of the square wave...it's bigger! (And so, THD is lower.)

This leads to something I didn't expect at all: if you feed an amplifier a sinewave, and gradually turn up the amplitude till clipping starts, and then push it further into clipping, the amplitude of that fundamental-frequency sinewave continues to increase!

-Gnobuddy

Gnobuddy
diyAudio Member

Join Date: Mar 2016
Quote:
 Originally Posted by PRR The value of the fundamental of a square wave is not 1.0 but 1.27. That does not cover the discrepancy, but reminds up that wave-smacking is not a simple thing.
You posted that while I was composing my last post...I think we both found the error I was making at about the same time.

-Gnobuddy

PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by Gnobuddy And that link contains the sentence "... THDF of 48.3%..."
I didn't *read* my own citation! Thanks for spotting that.

> fundamental-frequency sinewave continues to increase!

Intuitively: if you tune your ear to just the 1kHz, and crank past clipping, the 1kHz *does* increase. Yes, that's not normal hearing: the harmonics cloud perception, and we are used to just hearing "louder" without reference to the fundamental. I would not trust my ears either way (blind or knowing). Band-filter meter would tell; so could a tuned pipe (snip of garden-hose) on an SPL meter.

me> reminds up that wave-smacking

Sorry, "...reminds us that wave-smacking..."

forart.eu
diyAudio Member

Join Date: Apr 2009
Location: Marche
Quote:
 Originally Posted by Entas Hello, Checking some Power Amps, the one that I like the t.amp E-400 – Thomann Lithuania. Can I find better one than this? Is this thing actually have 190Wrms @ 4ohm?
What about Behringher A800 (2 x 400W @ 4ohms) which is a fanless Class-D reference studio amplifier available between 170-180€ ?

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