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Class D Switching Power Amplifiers and Power D/A conversion

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Old 2nd February 2014, 03:40 AM   #1
johanx2 is offline johanx2  United States
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Default Are class D amplifier only good for subwoofer speakers ?

Hi, I need to know if class D amplifier are only recommended for subwoofers. Can they also play middle and high frequencies as well ? Can I connect a 4 ohm 3-way speaker (with a woofer, mid-woofer and tweeter) to the output of a class D amplifier ?

Sorry for my nooby question, I did not find a sticky thread for general questions about class D amplifiers.
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Old 2nd February 2014, 04:51 AM   #2
Davet is offline Davet  United States
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I had never heard that class D should only be used for subwoofers. If what you state is true, I, and any number of others, have been terribly misled.

I believe the greater number of threads, here, reference Class D amps that are employed for the full audio range.
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Old 2nd February 2014, 05:09 AM   #3
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In the early days of Class D they were generally used in the subwoofer role because of their poor frequency response but nowadays they are used in full range applications.
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Old 2nd February 2014, 05:15 AM   #4
johanx2 is offline johanx2  United States
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Well I did not mean that, it's just I did not know if they could sound good at high frequencies or not. But tell me something about my other question. Can I connect several speakers in parallel to the output of a class D amplifier ? Of course, respecting the total impedance value. And I am not talking just about connecting subwoofers, what if I connect a subwoofer and a mid woofer with its tweteer to the output of the class D amp ?

Last edited by johanx2; 2nd February 2014 at 05:18 AM.
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Old 2nd February 2014, 05:19 AM   #5
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Quote:
Originally Posted by johanx2 View Post
Hi, I need to know if class D amplifier are only recommended for subwoofers. Can they also play middle and high frequencies as well ? Can I connect a 4 ohm 3-way speaker (with a woofer, mid-woofer and tweeter) to the output of a class D amplifier ?

Sorry for my nooby question, I did not find a sticky thread for general questions about class D amplifiers.
Yes, you can use a class D amplifier for full range. and yes, they are used in many sub-woofers brands too. Would I use one for my main amplifier?...NO!
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Old 2nd February 2014, 03:07 PM   #6
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Originally Posted by johanx2 View Post
Well I did not mean that, it's just I did not know if they could sound good at high frequencies or not.
Some do, but many are poor. (..and it is not just about high frequencies)
Simply read through the reviews - and find your taste.
Besides reading you should watch out for possibilities to listen to different designs. The differences are as large as they have been in the early transistorized class AB amps during the 1960s... or more optimistically like in the 70s...

In the mean time the ongoing evolution of class D amps is driven by the goals to achieve low cost and high power density.
Sonic improvements are of lowest interest for generation smart phone.
Consequently the situation of very different sonic quality is likely to last for decades.
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Old 2nd February 2014, 04:14 PM   #7
dewardh is offline dewardh  United States
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The better (Hypex or IRS2092 designs) Class D amps compete directly with the very best Class A amps. The lack of crossover (zero crossing) distortion and (typically) very low distortion overall means that they perform better than most (all but the best and most expensive) Class AB amps. Class D amps are rapidly taking over in the pro world, and not just because of their light weight and high efficiency . . . they sound good too.

That said . . . not all "consumer" Class D amps found in the typical HT receiver rise to that standard (of course the Class AB amps in those receivers are not necessarily "the best" either). And Class D can be (but isn't necessarily) somewhat more "load sensitive" and not respond well to speakers with poorly designed crossovers, although worth noting is that many Class A and Class AB amps have problems with low or variable impedance loads as well.

Of course there will always be some bottle heads out there to tell you that all "solid state" amps suck and the only way to get "good sound" is with some particular brand of EL84s or a single ended 2A3. Don't believe it . . .
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Old 2nd February 2014, 04:25 PM   #8
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I have designed class AB and class D amplifiers and cant tell the difference to be honest.

Class D is more efficient.

Careful design of the output filter reduces carrier on the output while at the same time passing higher audio frequencies.
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Old 2nd February 2014, 04:35 PM   #9
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Originally Posted by dewardh View Post
The lack of crossover (zero crossing) distortion and (typically) very low distortion overall means that they perform better than most (all but the best and most expensive) Class AB amps.
Class D has multiple distortion mechanisms, which do not exist in class AB.
And one of these is the dead time distortion, which causes distortion at the current levels were the output current starts to exceed the filter ripple current.
The related distortions are as ugly as crossover distortion.
-Then the distortion caused by the residuals, which are fed back to the input.
- ...further less dominant effects...

IMHO there is no simple reason why classD naturally would sound better.


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Originally Posted by dewardh View Post
Of course there will always be some bottle heads out there to tell you that all "solid state" amps suck and the only way to get "good sound" is with some particular brand of EL84s or a single ended 2A3. Don't believe it . . .

In fact I am a fan of classD and fell in love with a specific one, which simply kicks out all my older class AB amps with a smile.
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Old 2nd February 2014, 04:50 PM   #10
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One problem with class d is it can be a bit of a black art.

1/ Good pcb layout with powerplanes is vital due to high frequencies.
2/ Correct decoupling to mosfets, power supply and class d IC is vital.
3/ Output filter design needs to be spot on with correct inductor core type.

I fell down all these holes on my first attempt and it just kept on resetting on any level of power. I took 3 pcb revisions to get a amplifier that didnt reset on high power levels,

I can see where poor examples of class d amplifiers come from by my own problems.

I use the irs2092 and had a major problem with clicks, siren noises and thumps on power down when I used 20,000uF per supply rail. I had to contact IR to get help on this.
The solution was to add a small PIC with A2D and monitor VCC and if it was too low hold the 2092 in reset.
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