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Old 5th April 2012, 04:54 PM   #1
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Default Class D Amplifiers for tweeters ?

There's few manufacturers (like ADAM) who insist using Class AB for tweeters. I'm curious as I've heard nothing wrong with my Sure 4*100 Amps driving paralleled XT25 as part of my active 4-way dipoles. That's 2 ohms nominal load.

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I swapped the amplifiers with Gainclone 3875 and noticed that it's more airy. But soon it is clear why. The ClassD do not like being loaded so much at high frequency.

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The loss is first order lowpass, and very easily corrected with shelving highpass filter. This deviation does not happen with single tweeter (4ohms load)

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The correction gives back the airy sound.

It would be interesting if instant-switching of the amps were possible, but swapping them around I do not notice one being better than the other. Safe enough to say they sounded the same, and certainly nothing to draw attention to.
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Old 5th April 2012, 06:07 PM   #2
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The output filter in a class D amps is always designed to a specific load impedance. Loading it with a a different impedance will affect the high frequency cut-off point. Specifically loading it with half the impedance will halve the cut-out point, and this is what you have experienced here.

The fault therefore is not on the class D amp but on the user using it outside its specified working area. Find an amp that is designed for 2 ohm loads instead, or change the output filter.
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Old 10th April 2012, 08:28 AM   #3
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Yes, that's correct. However to compare, gainclones doesn't mind that.

The PDF of the comparison study is here:

ClassD vs Gainclone amplifiers

In summary, Class D is as good as linear amps even for tweeters.
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