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Class D Switching Power Amplifiers and Power D/A conversion

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Old 16th December 2010, 07:07 AM   #31
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Quote:
Originally Posted by Robert GS View Post
Can we agree that Class D hasn't high efficiency at low levels? Should be possible.
Depends on what we compare it with. If we exclude the power supply from the equation then all classes of amps scale exactly the same compared to output plus the needed bias and quiescent current of the circuit.

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And when measuring Class D it's allow to filter the output with low-pass filters - this isn't allow for the other Classes !
That's not exactly true, you can make filterless class D amps but output filters are most often used because it's a PWM or PDM amp. All classes of PWM or PDM amps usually has output filters to prevent the switching frequency from reaching the speakers.

There's nothing to stop you from using low-pass filters on the output of a PCM amp, it's just not necessitated by the design.
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Old 16th December 2010, 07:49 AM   #32
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My point is that the claim of high efficiency isn't viable for Class D because it's for audio signals that often are low compared to sin full level.

And I am not talking about output filters on the amplifier it self - it's filters inserted between the amplifier output (after the PWM amplifier own output filter) and the measurement system!
Don't get me wrong I like Class D for the right purpose and engineered right!
I have used Lab.Gruppen LAB2000, LAB2000C, LAB2002, LAB4000, fP6400 and fP+10000Q for nearly two decades - all with tracking Class D technology ! And at the same time their Class B for compression drivers, because of the better sound quality.

@ luka - year maybe clip is dumb, but this is reality in PA anyway. And I have seen this too in HiFi related equipment because of very low sensitive passive loudspeakers and to get a realistic reproduction of the music signal.

Tell us about your speakers. please!
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Old 16th December 2010, 08:10 AM   #33
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The reason why a filter is allowed for class-d maesurement is because the carrier residual simply increases THD measurement without actually having higher THD present. This is happening with both - old fashioned THD meters and DSP-based ones. The first ones simply measure the total amplitude of what is going on above the first harmonic and therefore include the carrier to some degree and the latter ones may have problems due to being sampling devices.
Speakers don't have these problems so it is valid to measure with a low pass in place IMO.

Regards

Charles
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Old 16th December 2010, 08:32 AM   #34
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I know - but it still discriminate the other classes when compared. AND neglecting this carrier residual can trigger a breakup in a tweeter EG at 22kHz might not be possible hear, but increases the tweeters THD = decreases the sound quality.
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Old 16th December 2010, 09:01 AM   #35
luka is offline luka  Slovenia
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like you can hear anything above 18k by age over 20
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Old 16th December 2010, 09:19 AM   #36
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Provoking a break up affects the performance further down in frequency (You are right - I can't hear that high - 22kHz)
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Old 17th December 2010, 12:01 PM   #37
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like you can hear anything above 18k by age over 20
Hi,
If you smear some oil on the surface of your speaker system (external of box), the voice spectrum changes completely. So, it is true that I can not hear over the 18K (single sound), but the harmonic component, that of course. is the harmonic component that defines the sound, which is why it is difficult to play well on a digital amp.

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Roberto P.
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