| Class D phase response [message #382214] |
Sun, 30 November 2008 02:09  |
 Darren Scaresbrook
Messages: 103
Registered: April 2004
Location: Australia |
Has No Life |
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Does anyone have any info on the phase response characteristics of class D amps?
I've searched the various manufacturers websites for data concerning this and found nothing. Due to the output filtering needed in these designs there must be some phase shift going on. I'm interested to know how much to find out if it will affect speaker alignment noticeably.
Darren
http://members.optusnet.com.au/~mdsaudio/
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| Re: Class D phase response [message #382469 is a reply to message #382372 ] |
Mon, 01 December 2008 10:26  |
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John Roberts {JR}
Messages: 7629
Registered: April 2004
Location: MS |
Has No Life |
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| Art Welter wrote on Sun, 30 November 2008 20:21 |
Peter,
Very interesting comparisons. Mixing amp brands may also need to be addressed by different delay settings to get phase traces exactly correct, it seems.
What does DIM100 Vs. Power 4 ohm mean? Is DIM100 inter modulation distortion?
The Lab Gruppen does a power reversal Vs % on that chart.
Then on the THD chart it does a power reversal at about 1.5%.
Is this due to a limiter that cuts power based on distortion?
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DIM100 is an obscure test that stresses slew rate. It mixes a sine wave with a square wave and looks for distortion on that sine wave during the square wave edges. This test is generally one that a product either does great or lousy depending on it's slew rate capability, and/or input filtering.
From inspection of the frequency response plots the FP6400 doesn't indicate an overall LPF like the other amps. I suspect even a modest LPF well above the audio band would probably clean up the DIM100 result, but this is just supposition on my part and not proved.
As a circuit designer myself, I never embraced the DIM tests as they involve out of band stimulus signals (square waves). That said I generally favor band passing the audio early in the signal path, so any square waves would be slowed down elsewhere well before getting to my power amp where they could cause mischief.
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All amps will have some HF phase shift under load due to protective load isolation series inductance in outputs. IIRC the crown will have an additional wide band delay due to A/D/A.
JR
https://www.resotune.com/
"A bus in a console is spelled with one 's', but you can buss your girlfriend while riding in a bus."
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