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Why can't a Sine Wave be used for testing high-power Class D amps?

bibio

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Hello,
As the title suggested, I don't understand why a sine wave can't be used to test modern, high-power, class d amplifiers.
Some of the large PA amps I've recently looked at have dsp build-in which appear to clamp down any waveform that looks like a continuous sine wave.
Would someone be able to explain the reasoning behind this? Is it the Class D amp or the SMPS that is the issue?
Considering the waveforms of some modern music, does this not affect the audio quality? Some synth music is very sinewave based. How does the DSP differentiate?
So if you can't use a sine wave, how could I perform a frequency sweep of an amplifier? I have one particular amp that has built-in dsp and speaker presets, I'd like to see the crossover point and such.
Thanks in advance for your help.
 

fpitas

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Amir does use a sine wave sweep to test FR. And a series of sine waves to test IMD. I'm not sure I understand your question.
 

fpitas

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Probably because they don’t want to deal with the associated warranty claims
Wait. Amir drives the amps all the way to clipping with sine waves.
 

fpitas

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Perhaps OP meant square wave testing?
 

Steve81

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As to how it works, use a real-time FFT to analyze the waveform, and set the threshold of user dumbassery you are willing to accept.
 

fpitas

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I feel like another conversation is going on that I can't see.
 

fpitas

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Look up what an FFT is, preferably with pics for better understanding. Then you’ll know how.
Huh? Now I'm really lost. A sine wave will just give a simple line.
 

fpitas

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Or is this an elaborate troll?
 

fpitas

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fpitas

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You're very rude.
 

Roland68

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Hello,
As the title suggested, I don't understand why a sine wave can't be used to test modern, high-power, class d amplifiers.
Some of the large PA amps I've recently looked at have dsp build-in which appear to clamp down any waveform that looks like a continuous sine wave.
Would someone be able to explain the reasoning behind this? Is it the Class D amp or the SMPS that is the issue?
Considering the waveforms of some modern music, does this not affect the audio quality? Some synth music is very sinewave based. How does the DSP differentiate?
So if you can't use a sine wave, how could I perform a frequency sweep of an amplifier? I have one particular amp that has built-in dsp and speaker presets, I'd like to see the crossover point and such.
Thanks in advance for your help.
Could you please post a link to the amp?
 

fpitas

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Here's a typical test done by Amir:

 

Everett T

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Perhaps OP meant square wave testing?
I've seen Gene at Audioholics post that certain high power Class D amps don't like sine wave testing, mentioning the Pascal modules but couldn't find where he explained why. He just noted his listening tests didn't jive with the measurements, whatever those conditions were.
 
Last edited:

fpitas

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JSmith

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... until the OP comes back.


JSmith
 

Steve81

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I've seen Gene at Audioholics post that certain high power Class D amps don't like some wave testing, mentioning the Pascal modules but couldn't find where he explained why. He just noted his listening tests didn't jive with the measurements, whatever those conditions were.

It really just depends on how the limiting thresholds are set, which varies from manufacturer to manufacturer. They don’t want Gene killing an amp any more than an idiot who thinks he’s clever (the most dangerous type).

On my subs, I have access to all that, but I never dared mess with Funk’s settings.
 
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